Object Oriented programming is a programming style which is associated with the concepts like class, object, Inheritance, Encapsulation, Abstraction, Polymorphism. Most popular programming languages like Java, C++, C#, Ruby, etc. follow an object-oriented programming paradigm. As Java being the most sought-after skill, we will talk about object-oriented programming concepts in Java. An object-based application in Java is based on declaring classes, creating objects from them and interacting between these objects. I have discussed Java Classes and Objects which is also a part of object-oriented programming concepts, in my previous blog. 

In this blog, we will understand the below core concepts of Object oriented Programming in the following sequence:

1. Inheritance
2. Encapsulation
3. Abstraction
4. Polymorphism

Let’s get started with the first Object Oriented Programming concept i.e. Inheritance.

Object Oriented Programming : Inheritance

In OOP, computer programs are designed in such a way where everything is an object that interact with one another. Inheritance is one such concept where the properties of one class can be inherited by the other. It helps to reuse the code and establish a relationship between different classes.

As we can see in the image, a child inherits the properties from his father. Similarly, in Java, there are two classes:

1. Parent class ( Super or Base class)

2. Child class (Subclass or Derived class )

A class which inherits the properties is known as Child Class whereas a class whose properties are inherited is known as Parent class.  

Inheritance is further classified into 4 types:

So let’s begin with the first type of inheritance i.e. Single Inheritance:

1. Single Inheritance:

In single inheritance, one class inherits the properties of another. It enables a derived class to inherit the properties and behavior from a single parent class. This will in turn enable code reusability as well as add new features to the existing code.

Here, Class A is your parent class and Class B is your child class which inherits the properties and behavior of the parent class.

Let’s see the syntax for single inheritance:

Class A
{
---
}
Class B extends A {
---
}

2. Multilevel Inheritance:

When a class is derived from a class which is also derived from another class, i.e. a class having more than one parent class but at different levels, such type of inheritance is called Multilevel Inheritance.

If we talk about the flowchart, class B inherits the properties and behavior of class A and class C inherits the properties of class B. Here A is the parent class for B and class B is the parent class for C. So in this case class C implicitly inherits the properties and methods of class A along with Class B. That’s what is multilevel inheritance.

Let’s see the syntax for multilevel inheritance in Java:

Class A{
---
}
Class B extends A{
---
}
Class C extends B{
---
}

3. Hierarchical Inheritance:

When a class has more than one child classes (sub classes) or in other words, more than one child classes have the same parent class, then such kind of inheritance is known as hierarchical.

If we talk about the flowchart, Class B and C are the child classes which are inheriting from the parent class i.e Class A.

Let’s see the syntax for hierarchical inheritance in Java:

Class A{
---
}
Class B extends A{
---
}
Class C extends A{
---
}

4. Hybrid Inheritance:
   

Hybrid inheritance is a combination of multiple inheritance and multilevel inheritance. Since multiple inheritance is not supported in Java as it leads to ambiguity, so this type of inheritance can only be achieved through the use of the interfaces. 

If we talk about the flowchart, class A is a parent class for class B and C, whereas Class B and C are the parent class of D which is the only child class of B and C.

Now we have learned about inheritance and their different types. Let’s switch to another object oriented programming concept i.e Encapsulation.

Object Oriented Programming : Encapsulation

Encapsulation is a mechanism where you bind your data and code together as a single unit. It also means to hide your data in order to make it safe from any modification. What does this mean? The best way to understand encapsulation is to look at the example of a medical capsule, where the drug is always safe inside the capsule. Similarly, through encapsulation the methods and variables of a class are well hidden and safe.

We can achieve encapsulation in Java by:

• Declaring the variables of a class as private.
• Providing public setter and getter methods to modify and view the variables values.

Let us look at the code below to get a better understanding of encapsulation:

public class Employee {
 private String name;
 public String getName() {
 return name;
 }
 public void setName(String name) {
 this.name = name;
 }
 public static void main(String[] args) {
 }
}

Let us try to understand the above code. I have created a class Employee which has a private variable name. We have then created a getter and setter methods through which we can get and set the name of an employee. Through these methods, any class which wishes to access the name variable has to do it using these getter and setter methods.

Let’s move forward to our third Object-oriented programming concept i.e. Abstraction.

Object Oriented Programming : Abstraction

Abstraction refers to the quality of dealing with ideas rather than events. It basically deals with hiding the details and showing the essential things to the user. If you look at the image here, whenever we get a call, we get an option to either pick it up or just reject it. But in reality, there is a lot of code that runs in the background. So you don’t know the internal processing of how a call is generated, that’s the beauty of abstraction. Therefore, abstraction helps to reduce complexity. You can achieve abstraction in two ways:

a) Abstract Class

b) Interface

Let’s understand these concepts in more detail.

Abstract class: Abstract class in Java contains the ‘abstract’ keyword. Now what does the abstract keyword mean? If a class is declared abstract, it cannot be instantiated, which means you cannot create an object of an abstract class. Also, an abstract class can contain abstract as well as concrete methods.
Note: You can achieve 0-100% abstraction using abstract class.

To use an abstract class, you have to inherit it from another class where you have to provide implementations for the abstract methods there itself, else it will also become an abstract class.

Let’s look at the syntax of an abstract class:

Abstract class Mobile {   // abstract class mobile
Abstract void run();      // abstract method

Interface: Interface in Java is a blueprint of a class or you can say it is a collection of abstract methods and static constants. In an interface, each method is public and abstract but it does not contain any constructor. Along with abstraction, interface also helps to achieve multiple inheritance in Java.
Note: You can achieve 100% abstraction using interfaces.

So an interface basically is a group of related methods with empty bodies. Let us understand interfaces better by taking an example of a ‘ParentCar’ interface with its related methods.

public interface ParentCar {
public void changeGear( int newValue);
public void speedUp(int increment);
public void applyBrakes(int decrement);
}

These methods need be present for every car, right? But their working is going to be different.

Let’s say you are working with manual car, there you have to increment the gear one by one, but if you are working with an automatic car, that time your system decides how to change gear with respect to speed. Therefore, not all my subclasses have the same logic written for change gear. The same case is for speedup, now let’s say when you press an accelerator, it speeds up at the rate of 10kms or 15kms. But suppose, someone else is driving a super car, where it increment by 30kms or 50kms. Again the logic varies. Similarly for applybrakes, where one person may have powerful brakes, other may not.

Since all the functionalities are common with all my subclasses, I have created an interface ‘ParentCar’ where all the functions are present. After that, I will create a child class which implements this interface, where the definition to all these method varies.

Next, let’s look into the functionality as to how you can implement this interface.
So to implement this interface, the name of your class would change to any particular brand  of a Car, let’s say I’ll take an “Audi”. To implement the class interface, I will use the ‘implement’ keyword as seen below:

public class Audi implements ParentCar {
int speed=0;
int gear=1;
public void changeGear( int value){
gear=value;
}
public void speedUp( int increment)
{
speed=speed+increment;
}
public void applyBrakes(int decrement)
{
speed=speed-decrement;
}
void printStates(){
System.out.println("speed:"+speed+"gear:"+gear);
}
public static void main(String[] args) {
// TODO Auto-generated method stub
Audi A6= new Audi();
A6.speedUp(50);
A6.printStates();
A6.changeGear(4);
A6.SpeedUp(100);
A6.printStates();
}
}

Here as you can see, I have provided functionalities to the different methods I have declared in my interface class. Implementing an interface allows a class to become more formal about the behavior it promises to provide. You can create another class as well, say for example BMW class which can inherit the same interface ‘car’ with different functionalities.

So I hope you guys are clear with the interface and how you can achieve abstraction using it.

Finally, the last Object oriented programming concept is Polymorphism.

Object Oriented Programming : Polymorphism

Polymorphism means taking many forms, where ‘poly’ means many and ‘morph’ means forms. It is the ability of a variable, function or object to take on multiple forms. In other words, polymorphism allows you define one interface or method and have multiple implementations.

Let’s understand this by taking a real-life example and how this concept fits into Object oriented programming.

Let’s consider this real world scenario in cricket, we know that there are different types of bowlers i.e. Fast bowlers, Medium pace bowlers and spinners. As you can see in the above figure, there is a parent class- BowlerClass and it has three child classes: FastPacer, MediumPacer and Spinner. Bowler class has bowlingMethod() where all the child classes are inheriting this method. As we all know that a fast bowler will going to bowl differently as compared to medium pacer and spinner in terms of bowling speed, long run up and way of bowling, etc. Similarly a medium pacer’s implementation of bowlingMethod() is also going to be different as compared to other bowlers. And same happens with spinner class.
The point of above discussion is simply that a same name tends to multiple forms. All the three classes above inherited the bowlingMethod() but their implementation is totally different from one another.

Polymorphism in Java is of two types: 

1. Run time polymorphism
2. Compile time polymorphism

Run time polymorphism: In Java, runtime polymorphism refers to a process in which a call to an overridden method is resolved at runtime rather than at compile-time. In this, a reference variable is used to call an overridden method of a superclass at run time. Method overriding is an example of run time polymorphism. Let us look  the following code to understand how the method overriding works:

public Class BowlerClass{
void bowlingMethod()
{
System.out.println(" bowler ");
}
public Class FastPacer{
void bowlingMethod()
{
System.out.println(" fast bowler ");
}
Public static void main(String[] args)
{
FastPacer obj= new FastPacer();
obj.bowlingMethod();
}
}

Compile time polymorphism: In Java, compile time polymorphism refers to a process in which a call to an overloaded method is resolved at compile time rather than at run time. Method overloading is an example of compile time polymorphism. Method Overloading is a feature that allows a class to have two or more methods having the same name but the arguments passed to the methods are different. Unlike method overriding, arguments can differ in:

1. Number of parameters passed to a method
2. Datatype of parameters
3. Sequence of datatypes when passed to a method.

Let us look at the following code to understand how the method overloading works:

class Adder {
Static int add(int a, int b)
{
return a+b;
}
static double add( double a, double b)
{
return a+b;
}

public static void main(String args[])
{
System.out.println(Adder.add(11,11));
System.out.println(Adder.add(12.3,12.6));
}
}

I hope you guys are clear with all the object oriented programming concepts that we have discussed above i.e inheritance, encapsulation, abstraction and polymorphism. Now you can make your Java application more secure, simple and re-usable using Java OOPs concepts. Do read my next blog on Java String where I will be explaining all about Strings and its various methods and interfaces.

Now that you have understood the Object Oriented Programming concepts in Java, check out the Java training by Edureka, a trusted online learning company with a network of more than 250,000 satisfied learners spread across the globe. Edureka’s Java J2EE and SOA training and certification course is designed for students and professionals who want to be a Java Developer. The course is designed to give you a head start into Java programming and train you for both core and advanced Java concepts along with various Java frameworks like Hibernate & Spring.

Got a question for us? Please mention it in the comments section of this “Object Oriented Programming” blog  and we will get back to you as soon as possible.

Out of keen interest in DevOps, I thought of coming up with a series of blogs that will educate you about the new culture being adopted in Software Development and help you understand what is it all about.

The DevOps Tutorial

This DevOps tutorial blog series will familiarize you with DevOps methodology & industry-wide used tools, required for DevOps Certification. In this blog, I will take you through the following things, which will be the base of the upcoming blogs:

• What led DevOps to come into existence
• Introduction of DevOps

Waterfall Model 

Let’s consider developing software in a traditional way using a Waterfall Model.

In the above diagram you will see the phases it will involve:

• ­In phase 1 – Complete Requirement is gathered and SRS is developed
• In phase 2 – This System is Planned and Designed using the SRS
• In phase 3 – Implementation of the System takes place
• In phase 4 – System is tested and its quality is assured
• In phase 5 – System is deployed to the end users
• In phase 6 – Regular Maintenance of the system is done

Waterfall Model Challenges

The Water-fall model worked fine and served well for many years however it had some challenges. In the following diagram the challenges of Waterfall Model are highlighted.

In the above diagram you can see that both Development and Operations had challenges in the Waterfall Model.  From Developers point of view there were majorly two challenges:

After Development, the code deployment time was huge.

Pressure of work on old, pending and new code was high because development and deployment time was high.

On the other hand, Operations was also not completely satisfied. There were four major challenges they faced as per the above diagram:

It was difficult to maintain ~100% uptime of the production environment.

Infrastructure Automation tools were not very affective.

Number of severs to be monitored keeps on increasing with time and hence the complexity.

It was very difficult to provide feedback and diagnose issue in the product.

In the following diagram proposed solution to the challenges of Waterfall Model are highlighted.

In the above diagram, Probable Solutions for the issues faced by Developers and Operations are highlighted in blue. This sets the guidelines for an Ideal Software Development strategy.

From Developers point of view:

A system which enables code deployment without any delay or wait time.

A system where work happens on the current code itself i.e. development sprints are short and well planned.

From Operations point of view:

System should have at-least 99% uptime.

Tools & systems are there in place for easy administration.

Effective monitoring and feedbacks system should be there.

Better Collaboration between Development & Operations and is common requirement for Developers and Operations team.

I guess it’s time we explore what is DevOps and how it overcomes these challenges. Check out the below video on What is DevOps before you go ahead. 

DevOps integrates developers and operations team to improve collaboration and productivity. 

According to the DevOps culture, a single group of Engineers (developers, system admins, QA’s. Testers etc turned into DevOps Engineers) has end to end responsibility of the Application (Software) right from gathering the requirement to development, to testing, to infrastructure deployment, to application deployment and finally monitoring & gathering feedback from the end users, then again implementing the changes.

This is a never ending cycle and the logo of DevOps makes perfect sense to me. Just look at the above diagram – What could have been a better symbol than infinity to symbolize DevOps?

Now let us see how DevOps takes care of the challenges faced by Development and Operations. Below table describes how DevOps addresses Dev Challenges. 

DevOps Tutorial Table 1 – Above table states how DevOps solves Dev Challenges

Going further, below table describes how DevOps addresses Ops Challenges.

DevOps Tutorial Table 2 – Above table states how DevOps solves Ops Challenges

However, you would still be wondering, how to implement DevOps. To expedite and actualize DevOps process apart from culturally accepting it, one also needs various DevOps tools like Puppet, Jenkins, GIT, Chef, Docker, Selenium, AWS etc to achieve automation at various stages which helps in achieving Continuous Development, Continuous Integration, Continuous Testing, Continuous Deployment, Continuous Monitoring to deliver a quality software to the customer at a very fast pace.  

Now take a look at the below DevOps diagram with various DevOps Tools closely and try to decode it.

These tools has been categorized into various stages of DevOps. Hence it is important that I first tell you about DevOps stages and then talk more about DevOps Tools.

DevOps Lifecycle can be broadly broken down into the below DevOps Stages:

• Continuous Development
• Continuous Integration
• Continuous Testing
• Continuous Monitoring
• Virtualization and Containerization

These stages are the building blocks to achieve DevOps as a whole.

This is the end of the first blog of – The DevOps Tutorial Series. 

To know more on DevOps Stages, Click here to visit the second blog – What is DevOps and Its Stages ?

Got a question for us? Please mention it in the comments section and we will get back to you.

As of Jan 2019, Salesforce is the world’s leading CRM service provider. They have more than 40% market share in the Cloud CRM space and dominates the overall CRM space with a market share of 19.7%. They were rated the world’s #1 CRM for two consecutive years and if the projected growth of Salesforce is anything to go by, the need for professionals with Salesforce training is only going to exponentially increase. This is where Salesforce enters the picture, and that is what has prompted me to write a blog on the most frequently asked Salesforce interview questions.

Thanks to the knowledge and wisdom shared by some of our experts from the industry, I have shortlisted this definitive list of the Top 50 Salesforce interview questions which will help you breeze through your interview. Hopefully this helps you land a top-notch job in the domain of your passion. In case you attended a Salesforce interview recently, we urge you to post any question you have faced. Our experts will be happy to answer them for you.

Top 50 Salesforce Interview Questions And Answers

This list of Salesforce interview questions is divided into 9 sections, each for different aspects of Salesforce.

1. Salesforce fundamentals
2. Declarative features
3. Audit & reporting features
4. Data modelling and data management
5. Logic & process automation
6. Software testing
7. Debug & deployment tools
8. Integration features
9. Programmatic features

A. Salesforce Fundamentals – Salesforce Interview Questions

1. Can two users have the same profile? Can two profiles be assigned to the same user?

Profiles determine the level of access a user can have in a Salesforce org.

As far as the first part of the question is concerned, Yes. One profile can be assigned to any number of users. Take the example of a Sales or Service team in a company. The entire team will be assigned the same profile. The admin can create one profile: Sales Profile, which will have access to the Leads, Opportunities, Campaigns, Contacts and other objects deemed necessary by the company.

In this way, many users can be assigned the same profile. In case the team lead or manager need access to additional records/ objects then it can be done by assigning permission sets only for those users.

Answering the second part of the question, each user can only be assigned 1 profile.

2. What are Governor Limits in Salesforce?

In Salesforce, it is the Governor Limits which controls how much data or how many records you can store in the shared databases. Why? Because Salesforce is based on the concept of multi-tenant architecture. In simpler words, Salesforce uses a single database to store the data of multiple clients/ customers. The below image will help you relate to this concept.

To make sure no single client monopolizes the shared resources, Salesforce introduced the concept of Governor Limits which is strictly enforced by the Apex run-time engine.

Governor Limits are a Salesforce developer’s biggest challenge. That is because if the Apex code ever exceeds the limit, the expected governor issues a run-time exception that cannot be handled. Hence as a Salesforce developer, you have to be very careful while developing your application.

Different Governor Limits in Salesforce are:

• Per-Transaction Apex Limits
• Force.com Platform Apex Limits
• Static Apex Limits
• Size-Specific Apex Limits
• Miscellaneous Apex Limits
• Email Limits
• Push Notification Limits

3. What is a sandbox org? What are the different types of sandboxes in Salesforce?

A sandbox is a copy of the production environment/ org, used for testing and development purposes. It’s useful because it allows development on Apex programming without disturbing the production environment.

When can you use it?
You can use it when you want to test a newly developed Force.com application or Visualforce page. You can develop and test it in the Sandbox org instead of doing it directly in production.

This way, you can develop the application without any hassle and then migrate the metadata and data (if applicable) to the production environment. Doing this in a non-production environment allows developers to freely test and experiment applications end to end.

Types of Sandboxes are:

• Developer
• Developer Pro
• Partial Copy
• Full

4. Can you edit an apex trigger/ apex class in production environment? Can you edit a Visualforce page in production environment?

No, it is not possible to edit apex classes and triggers directly in production environment.

It needs to be done first in Developer edition or testing org or in Sandbox org. Then, to deploy it in production, a user with Author Apex permission must deploy the triggers and classes using deployment tools.

However, Visualforce pages can be created and edited in both sandbox and in production.

Only if the page has to do something unique (different values), it would have to be developed via Sandbox.

5. What are the different data types that a standard field record name can have?

A standard field record name can have data type of either auto number or text field with a limit of 80 chars.

For generating auto numbers, the format needs to be specified while defining the field and after that for every record that is added, the number will get auto generated. For example:-
Sr No-{1}
Sr No-{2}
Sr No-{3}

6. Why are Visualforce pages served from a different domain?

Visualforce pages are served from a different domain to improve security standards and block cross site scripting. Take a look at the highlighted portion in the below Visualforce page:-

B. Declarative Features – Salesforce Interview Questions

7. What is WhoId and WhatId in activities?

WhoID refers to people. Typically: contacts or leads. Example: LeadID, ContactID

WhatID refers to objects. Example: AccountID, OpportunityID

8. What is the use of writing sharing rules? Can you use sharing rules to restrict data access?

Sharing rules are written to give edit access (public read and write) or public read only access to certain individuals in Salesforce org. A classic example is when:- only your managers or superiors need to be given extra credentials to your records in objects as compared to your peers.

By default, all users in your organization will have organization-wide-default sharing settings of either Public Read Only or Private.
To give access to more records, which users do not own, we write sharing rules.
Example: Sharing rules are used to extend sharing access to users in public groups or roles. Hence, sharing rules are not as strict as organization-wide default settings. They allow greater access for those users.

As far as the second part of the question is concerned, the answer is no. We cannot use sharing rules to restrict data access. It is only used for allowing greater access to records.

9. What are the different types of email templates that can be created in Salesforce?

The different types of Email templates are listed in the below table:-

C. Audit & Reporting Features – Salesforce Interview Questions

10. What is a bucket field in reports?

A bucket field lets you group related records together by ranges and segments, without the use of complex formulas and custom fields. Bucketing can thus be used to group, filter, or arrange report data. When you create a bucket field, you need to define multiple categories (buckets) that are used to group report values.

The advantage is that earlier, we had to create custom fields to group or segment certain data.

11. What are dynamic dashboards? Can dynamic dashboards be scheduled?

Before we understand dynamic dashboards, let us first understand static dashboards. Static dashboards are the basic dashboard types that will be visible to any user who has made a report out of his data. An example of this is what a Sales manager/ Marketing manager would be able to see on his Salesforce org. In other words, a normal dashboard shows data only from a single user’s perspective. Now comes the concept of dynamic dashboards.

Dynamic dashboards are used to display information which is tailored to a specific user. Let us consider the same example as above. In case the Sales manager wants to view the report generated specific to only one of his team members, then he can use dynamic dashboards.

You can use dynamic dashboards when you want to show user-specific data of a particular user, such as their personal quotas and sales, or number of case closures, or leads converted etc.
You can also use a normal/ static dashboard when you want to show regional or organization-wide data to a set of users, such as a particular region’s sales number, or a particular support team’s performance on case closures.

As far as the second part of the question is concerned, no we cannot schedule a dynamic dashboard. That is because whenever we open the dashboard, it will show the data generated in real-time.

12. What are the different types of reports available in Salesforce? Can we mass delete reports in Salesforce?

Another important point to note here is that, only Summary reports and Matrix reports can be fed as data source for dashboards. Tabular and Joined reports cannot be used as data source for dashboards.

Can we mass delete reports in Salesforce? Of Course we can mass delete reports in Salesforce. The option to mass delete reports can be found under Data Management in Setup.

D. Data Modelling & Data Management – Salesforce Interview Questions

13. What are the different types of object relations in salesforce? How can you create them?

No list of Salesforce interview questions is complete without involving relationships between objects in Salesforce. Relationships in Salesforce can be used to establish links between two or more objects.

The different types of object relationships in Salesforce are:

1. Master-Detail Relationship (1:n):- It is a parent-child relationship in which the master object controls the behavior of the dependent child object. It is a 1:n relationship, in which there can be only one parent, but many children.The main concept you need to be know is that, being the controlling object, the master field cannot be empty. If a record/ field in master object is deleted, the corresponding fields in the dependent object are also deleted. This is called a cascade delete. Dependent fields will inherit the owner, sharing and security settings from its master.You can define master-detail relationships between two custom objects, or between a custom object and standard object as long as the standard object is the master in the relationship.
2. Lookup Relationship (1:n):-
   Lookup relationships are used when you want to create a link between two objects, but without the dependency on the parent object. Similar to Master-Detail relationship, you can think of this as a form of parent-child relationship where there is only one parent, but many children i.e. 1:n relationship.The difference here is that despite being controlling field, deleting a record will not result in automatic deletion of the lookup field in the child object. Thus the records in the child object will not be affected and there is no cascade delete here. Neither will the child fields inherit the owner, sharing or security settings of its parent.
   
3. Junction Relationship (Many-To-Many):-
   This kind of a relationship can exist when there is a need to create two master-detail relationships. Two master-detail relationships can be created by linking 3 custom objects. Here, two objects will be master objects and the third object will be dependent on both the objects. In simpler words, it will be a child object for both the master objects.

14. What happens to detail record when a master record is deleted? What happens to child record when a parent record is deleted?

In a Master-Detail relationship, when a master record is deleted, the detail record is deleted automatically (Cascade delete).

In a Lookup relationship, even if the parent record is deleted, the child record will not be deleted.

15. Can you have a roll up summary field in case of Master-Detail relationship?

Yes. You can have a roll-up summary in case of a master-detail relationship. But not in case of a lookup relationship.

A roll-up summary field is used to display a value in a master record based on the values of a set of fields in a detail record. The detail record must be related to the master through a master-detail relationship.

There are 4 calculations that you can do using roll-up summary field. You can count the number of detail records related to a master record. Or, you can calculate the sum, minimum value, or maximum value of a field in the detail records.

16. Explain the term “Data Skew” in Salesforce.

“Data skew” is a condition which you will encounter when working for a big client where there are over 10,000 records. When one single user owns that many records we call that condition ‘ownership data skew’.

When such users perform updates, performance issues will be encountered because of “data skew”. This happens when a single user/ members of a single role own most of the records for a particular object.

17. Explain skinny table. What are the considerations for Skinny Table?

In Salesforce, skinny tables are used to access frequently used fields and to avoid joins. This largely improves performance. Skinny tables are highly effective, so much so that even when the source tables are modified, skinny tables will be in sync with source tables.

Considerations for skinny tables:

• Skinny tables can contain a maximum of 100 columns.
• Skinny tables cannot contain fields from other objects.
• For full sandboxes: Skinny tables are copied to your Full sandbox organizations, as of the Summer ’15 release.

18. Which fields are automatically Indexed in Salesforce?

Only the following fields are automatically indexed in Salesforce:

• Primary keys (Id, Name and Owner fields).
• Foreign keys (lookup or master-detail relationship fields).
• Audit dates (such as SystemModStamp).
• Custom fields marked as an External ID or a unique field.

19. How to handle comma within a field while uploading using Data Loader?

In a Data Loader .CSV, if there is a comma in field content, you will have to enclose the contents within double quotation marks: ” “.

E. Logic & Process Automation – Salesforce Interview Questions

20. For which criteria in workflow “time dependent workflow action” cannot be created?

Time dependent workflow action cannot be create for: “created, and every time it’s edited”.

21. What are the types of custom settings in Salesforce? What is the advantage of using custom settings?

There are two types of custom settings in Salesforce: List Custom Settings and Hierarchy Custom Settings.

List Custom Settings are a type of custom settings that provides a reusable set of static data that can be accessed across your organization irrespective of user/ profile.
Hierarchy Custom Settings are another type of custom settings that uses built-in hierarchical logic for “personalizing” settings for specific profiles or users.

The advantage of using custom settings is that it allows developers to create a custom set of access rules for various users and profiles.

22. How many active assignment rules can you have in a lead/ case?

Only one rule can be active at a time.

23. What are custom labels in Salesforce? What is the character limit of custom label?

Custom labels are custom text values that can be accessed from Apex classes or Visualforce pages. The values here can be translated into any language supported by Salesforce.
Their benefit is that they enable developers to create multilingual applications which automatically presents information in a user’s native language.

You can create up to 5,000 custom labels for your organization, and they can be up to 1,000 characters in length.

24. What is the difference between a Role and Profile in Salesforce?

As mentioned in one of the previous Salesforce interview questions, a profile will ultimately control access to which records a user has in a Salesforce org. No user can work on the Salesforce org without being assigned a profile. The Profile is therefore mandatory for every user.

Role however is not mandatory for every user. The primary function of the Role/ Role hierarchy is that it allows higher level users in hierarchy get access to records owned by lower level users in the hierarchy. An example of that is Sales Managers getting access to records owned by Sales Reps while their peers do not get access to it.

25. What are the examples of non-deterministic Force.com formula fields?

Before I mention some of the examples, let me give you an introduction to deterministic and non-deterministic formula fields. Formula fields whose value will be static are referred to as deterministic fields. Whereas, formula fields whose value will be changed dynamically or whose values will have to be calculated on the fly, they are referred to as non-deterministic formula fields. A classic example of that is a formula returning the current date and time.

Some examples of non-deterministic fields in Force.com are:

• Lookup fields
• Formula fields whose reference spans over other entities
• Fields having dynamic date functions like:- TODAY() or NOW()

F. Software Testing – Salesforce Interview Questions

26. Why do we need to write test classes? How to identify if a class is a test class?

Software developers from around the world will unanimously agree that writing code in test classes makes debugging more efficient. Why? That is because test classes help in creating robust and error-free code be it Apex or any other programming language. Since Unit tests are powerful in their own right, Salesforce requires you to write test classes in Apex code.

Why are they so powerful? Because test classes and test methods verify whether a particular piece of code is working properly or not. If that piece of code fails, then developers/ testers can accurately locate the test class having the faulty bug.

Test classes can be determined easily because every test class will be annotated with @isTest keyword. In fact, if we do not annotate a test class with @isTest, then it cannot be defined as a test class. Similarly, any method within a class which has the keyword testMethod, is a test method.

27. What is minimum test coverage required for trigger to deploy?

In Salesforce, if you want to deploy your code to production, then you must make sure that at least 75% of your Apex code is covered by unit tests. And all these tests must complete successfully.

G. Debug & Deployment Tools – Salesforce Interview Questions

28. What are the different ways of deployment in Salesforce?

You can deploy code in Salesforce using:

1. Change Sets
2. Eclipse with Force.com IDE
3. Force.com Migration Tool – ANT/Java based
4. Salesforce Package

H. Integration – Salesforce Interview Questions

29. What is an external ID in Salesforce? Which all field data types can be used as external IDs?

An external ID is a custom field which can be used as a unique identifier in a record. External IDs are mainly used while importing records/ data. When importing records, one among the many fields in those records need to be marked as an external ID (unique identifier).

An important point to note is that only custom fields can be used as External IDs. The fields that can be marked as external IDs are: Text, Number, E-Mail and Auto-Number.

30. How many callouts to external service can be made in a single Apex transaction?

Governor limits will restrict a single Apex transaction to make a maximum of 100 callouts to an HTTP request or an API call.

31. How can you expose an Apex class as a REST WebService in Salesforce?

You can expose your Apex class and methods so that external applications can access your code and your application through the REST architecture. This is done by defining your Apex class with the @RestResource annotation to expose it as a REST resource. You can then use global classes and a WebService callback method.

Invoking a custom Apex REST Web service method always uses system context. Consequently, the current user’s credentials are not used, and any user who has access to these methods can use their full power, regardless of permissions, field-level security, or sharing rules.

Developers who expose methods using the Apex REST annotations should therefore take care that they are not inadvertently exposing any sensitive data. Look at the below piece of code for instance:-

global class AccountPlan {
 webservice String area; 
 webservice String region; 
 //Define an object in apex that is exposed in apex web service
 global class Plan {
 webservice String name;
 webservice Integer planNumber;
 webservice Date planningPeriod;
 webservice Id planId;
 }
 webservice static Plan createAccountPlan(Plan vPlan) {
 //A plan maps to the Account object in salesforce.com. 
 //So need to map the Plan class object to Account standard object
 Account acct = new Account();
 acct.Name = vPlan.name;
 acct.AccountNumber = String.valueOf(vPlan.planNumber);
 insert acct;
 vPlan.planId=acct.Id;
 return vPlan;
 } }

I. Programmatic Features – Salesforce Interview Questions

32. What is the difference between a standard controller and a custom controller?

Standard controller in Apex, inherits all the standard object properties and standard button functionality directly. It contains the same functionality and logic that are used for standard Salesforce pages.

Custom controller is an Apex class that implements all of the logic for a page without leveraging a standard controller. Custom Controllers are associated with Visualforce pages through the controller attribute.

33. How can we implement pagination in Visualforce?

To control the number of records displayed on each page, we use pagination. By default, a list controller returns 20 records on the page. To customize it, we can use a controller extension to set the pageSize. Take a look at the sample code below:-

<apex:page standardController="Account" recordSetvar="accounts">
 <apex:pageBlock title="Viewing Accounts">
 <apex:form id="theForm">
 <apex:pageBlockSection >
 <apex:dataList var="a" value="{!accounts}" type="1">
 {!a.name}
 </apex:dataList>
 </apex:pageBlockSection>
 <apex:panelGrid columns="2">
 <apex:commandLink action="{!previous}">Previous</apex:commandlink>
 <apex:commandLink action="{!next}">Next</apex:commandlink>
 </apex:panelGrid>
 </apex:form>
 </apex:pageBlock>
</apex:page>

34. How can you call a controller method from JavaScript?

To call a controller method (Apex function) from JavaScript, you need to use actionfunction.

Look at the below piece of code to understand how a controller method is called using actionfunction.

 





<script>
function JSmethodCallFromAnyAction()
{
callfromJS();
}
</apex:page>

35. How to get the UserID of all the currently logged in users using Apex code?

You can get the ID’s of all the currently logged in users by using this global function: UserInfo.getUserId().

36. How many records can a select query return? How many records can a SOSL query return?

The Governor Limits enforces the following:-

Maximum number of records that can be retrieved by SOQL command: 50,000.

Maximum number of records that can be retrieved by SOSL command: 2,000.

37. What is an attribute tag? What is the syntax for including them?

An attribute tag is a definition of an attribute of a custom component and it can only be a child of a component tag.

Note that you cannot define attributes with names like id or rendered. These attributes are automatically created for all custom component definitions. The below piece of code shows the syntax for including them:

<apex:component>
 <apex:attribute name="myValue" description="This is the value for the component." type="String" required="true"/>
 <apex:attribute name="borderColor" description="This is color for the border." type="String" required="true"/>
 
</p>
<p>
</p>
<h1 style="border:{!borderColor}">
 <apex:outputText value="{!myValue}"/>
 </h1>
<p>
</p>
<p>

</apex:component>

38. What are the three types of bindings used in Visualforce? What does each refer to?

There are three types of bindings used in Salesforce:-

• Data bindings, which refer to the data set in the controller
• Action bindings, which refer to action methods in the controller
• Component bindings, which refer to other Visualforce components.

Data bindings and Action bindings are the most common and they will be used in every Visualforce page.

39. What are the different types of collections in Apex? What are maps in Apex?

Collections are the type of variables which can be used to store multiple number of records (data).

It is useful because Governor Limits restrict the number of records you can retrieve per transaction. Hence, collections can be used to store multiple records in a single variable defined as type collection and by retrieving data in the form of collections, Governor Limits will be in check. Collections are similar to how arrays work.

There are 3 collection types in Salesforce:

• Lists
• Maps
• Sets

Maps are used to store data in the form of key-value pairs, where each unique key maps to a single value.
Syntax: Map<String, String> country_city = new Map<String, String>();

40. How can you embed a Visualflow in a Visualforce page?

1. Find the flow’s unique name.

   1. From Setup, enter Flows in the Quick Find box, then select Flows.
   2. Click the name of the flow.
   3. Copy the unique name of the flow.

2. From Setup, enter Visualforce Pages in the Quick Find box, then select Visualforce Pages.

3. Define a new Visualforce page, or open an existing one.

4. Add the <flow:interview> component somewhere between the <apex:page> tags.

5. Set the name attribute to the unique name of the flow.

For example:

 </apex:page>
 <flow:interview name="flowuniquename"/>
 <apex:page>

6. Click Save.

7. Restrict which users can access the Visualforce page.

   1. Click Visualforce Pages.
   2. Click Security next to your Visualforce page.
   3. Move all the appropriate profiles from Available Profiles to Enabled Profiles by using the ‘add’ and ‘remove’ buttons.
   4. Click Save.

8. Add the Visualforce page to your Force.com app by using a custom button, link, or Visualforce tab.

41. What is the use of “@future” annotation?

Future annotations are used to identify and execute methods asynchronously. If the method is annotated with “@future”, then it will be executed only when Salesforce has the available resources.

For example, you can use it while making an asynchronous web service callout to an external service. Whereas without using the annotation, the web service callout is made from the same thread that is executing the Apex code, and no additional processing will occur until that callout is complete (synchronous processing).

42. What are the different methods of batch Apex class?

Database.Batchable interface contains three methods that must be implemented:

1. Start method:
   global (Database.QueryLocator | Iterable<sObject>) start(Database.BatchableContext bc) {}
2. Execute method:
   global void execute(Database.BatchableContext BC, list<P>){}
3. Finish method:
   global void finish(Database.BatchableContext BC){}

43. What is a Visualforce component?

A Visualforce Component is either a predefined component (standard from component library) or a custom component that determines the user interface behavior. For example, if you want to send the text captured from the Visualforce page to an object in Salesforce, then you need to make use of Visualforce components. Example: <apex:detail>

44. What is Trigger.new?

Triger.new is a command which returns the list of records that have been added recently to the sObjects. To be more precise, those records will be returned which are yet to be saved to the database. Note that this sObject list is only available in insert and update triggers, and the records can only be modified in before triggers.

But just for your information, Trigger.old returns a list of the old versions of the sObject records. Note that this sObject list is only available in update and delete triggers.

45. What all data types can a set store?

Sets can have any of the following data types:

• Primitive types
• Collections
• sObjects
• User-defined types
• Built-in Apex types

46. What is an sObject type?

An sObject is any object that can be stored in the Force.com platform database. Apex allows the use of generic sObject abstract type to represent any object.

For example, Vehicle is a generic type and Car, Motor Bike all are concrete types of Vehicle.
In SFDC, sObject is generic and Account, Opportunity, CustomObject__c are its concrete type.

47. What is the difference between SOQL and SOSL?

The differences are mentioned in the table below:

48. What is an Apex transaction?

An Apex transaction represents a set of operations that are executed as a single unit. The operations here include the DML operations which are responsible for querying records. All the DML operations in a transaction either complete successfully, or if an error occurs even in saving a single record, then the entire transaction is rolled back.

49. What is the difference between public and global class in Apex?

Global class is accessible across the Salesforce instance irrespective of namespaces.
Whereas, public classes are accessible only in the corresponding namespaces.

50. What are getter methods and setter methods?

Get (getter) method is used to pass values from the controller to the VF page.
Whereas, the set (setter) method is used to set the value back to controller variable.

I hope this set of Salesforce interview questions will help you ace your job interview. As the next step for your career, check out the various certifications offered by Salesforce here: Salesforce Certifications. It will also help you to understand the job roles and chalk out a career path for yourself. 

Also, check out this video on the Top 50 Frequently Asked Salesforce Interview Questions which was delivered by an industry expert. He has shared his opinion of Salesforce job interviews and industry demand. Do take a at it look and let us know if this helped in your interview preparation.

Got a question for us? Please mention it in the comments section and we will get back to you.

Top 50 Hadoop Interview Questions for 2019

In this Hadoop interview questions blog, we will be covering all the frequently asked questions that will help you ace the interview with their best solutions. But before that, let me tell you how the demand is continuously increasing for Big Data and Hadoop experts. You can check out this skill report which talks about the top technical skills to master in 2019.

Following are a few stats that reflect the growth in the demand for Big Data & Hadoop certification quite accurately:

• Big Data will drive $48.6 billion in annual spending by 2019- IDC.
• Average salary of a Big Data Hadoop developer in the US is $135k- Indeed.com
• Average annual salary in the United Kingdom is £66,250 – £66,750- itjobswatch.co.uk

I would like to draw your attention towards the Big Data revolution. Earlier, organizations were only concerned about operational data, which was less than 20% of the whole data. Later, they realized that analyzing the whole data will give them better business insights & decision-making capability. That was the time when big giants like Yahoo, Facebook, Google, etc. started adopting Hadoop & Big Data related technologies. In fact, nowadays one of every fifth company is moving to Big Data analytics. Hence, the demand for jobs in Big Data Hadoop is rising like anything. Therefore, if you want to boost your career, Hadoop and Spark are just the technology you need. This would always give you a good start either as a fresher or experienced.

Prepare with these top Hadoop interview questions to get an edge in the burgeoning Big Data market where global and local enterprises, big or small, are looking for the quality Big Data and Hadoop experts. This definitive list of top Hadoop interview questions will take you through the questions and answers around Hadoop Cluster, HDFS, MapReduce, Pig, Hive, HBase. This blog is the gateway to your next Hadoop job.

In case you have come across a few difficult questions in a Hadoop interview and are still confused about the best answer, kindly put those questions in the comment section below. We will be happy to answer them.

In the meantime, you can maximize the Big Data Analytics career opportunities that are sure to come your way by taking Hadoop online training with Edureka.  Click below to know more.

1. What are the basic differences between relational database and HDFS?

Here are the key differences between HDFS and relational database:

2. Explain “Big Data” and what are five V’s of Big Data?

“Big data” is the term for a collection of large and complex data sets, that makes it difficult to process using relational database management tools or traditional data processing applications. It is difficult to capture, curate, store, search, share, transfer, analyze, and visualize Big data. Big Data has emerged as an opportunity for companies. Now they can successfully derive value from their data and will have a distinct advantage over their competitors with enhanced business decisions making capabilities.

♣ Tip: It will be a good idea to talk about the 5Vs in such questions, whether it is asked specifically or not!

• Volume: The volume represents the amount of data which is growing at an exponential rate i.e. in Petabytes and Exabytes. 
• Velocity: Velocity refers to the rate at which data is growing, which is very fast. Today, yesterday’s data are considered as old data. Nowadays, social media is a major contributor to the velocity of growing data.
• Variety: Variety refers to the heterogeneity of data types. In another word, the data which are gathered has a variety of formats like videos, audios, csv, etc. So, these various formats represent the variety of data.
• Veracity: Veracity refers to the data in doubt or uncertainty of data available due to data inconsistency and incompleteness. Data available can sometimes get messy and may be difficult to trust. With many forms of big data, quality and accuracy are difficult to control. The volume is often the reason behind for the lack of quality and accuracy in the data.
• Value: It is all well and good to have access to big data but unless we can turn it into a value it is useless. By turning it into value I mean, Is it adding to the benefits of the organizations? Is the organization working on Big Data achieving high ROI (Return On Investment)? Unless, it adds to their profits by working on Big Data, it is useless.

As we know Big Data is growing at an accelerating rate, so the factors associated with it are also evolving. To go through them and understand it in detail, I recommend you to go through Big Data Tutorial blog.

3. What is Hadoop and its components. 

When “Big Data” emerged as a problem, Apache Hadoop evolved as a solution to it. Apache Hadoop is a framework which provides us various services or tools to store and process Big Data. It helps in analyzing Big Data and making business decisions out of it, which can’t be done efficiently and effectively using traditional systems.

♣ Tip: Now, while explaining Hadoop, you should also explain the main components of Hadoop, i.e.:

• Storage unit– HDFS (NameNode, DataNode)
• Processing framework– YARN (ResourceManager, NodeManager)

4. What are HDFS and YARN?

HDFS (Hadoop Distributed File System) is the storage unit of Hadoop. It is responsible for storing different kinds of data as blocks in a distributed environment. It follows master and slave topology.

♣ Tip: It is recommended to explain the HDFS components too i.e.

• NameNode: NameNode is the master node in the distributed environment and it maintains the metadata information for the blocks of data stored in HDFS like block location, replication factors etc.
• DataNode: DataNodes are the slave nodes, which are responsible for storing data in the HDFS. NameNode manages all the DataNodes.

YARN (Yet Another Resource Negotiator) is the processing framework in Hadoop, which manages resources and provides an execution environment to the processes.

♣ Tip: Similarly, as we did in HDFS, we should also explain the two components of YARN:   

• ResourceManager: It receives the processing requests, and then passes the parts of requests to corresponding NodeManagers accordingly, where the actual processing takes place. It allocates resources to applications based on the needs.
• NodeManager: NodeManager is installed on every DataNode and it is responsible for the execution of the task on every single DataNode.

If you want to learn in detail about HDFS & YARN go through Hadoop Tutorial blog.

5. Tell me about the various Hadoop daemons and their roles in a Hadoop cluster.

Generally approach this question by first explaining the HDFS daemons i.e. NameNode, DataNode and Secondary NameNode, and then moving on to the YARN daemons i.e. ResorceManager and NodeManager, and lastly explaining the JobHistoryServer.

• NameNode: It is the master node which is responsible for storing the metadata of all the files and directories. It has information about blocks, that make a file, and where those blocks are located in the cluster.
• Datanode: It is the slave node that contains the actual data.
• Secondary NameNode: It periodically merges the changes (edit log) with the FsImage (Filesystem Image), present in the NameNode. It stores the modified FsImage into persistent storage, which can be used in case of failure of NameNode.
• ResourceManager: It is the central authority that manages resources and schedule applications running on top of YARN.
• NodeManager: It runs on slave machines, and is responsible for launching the application’s containers (where applications execute their part), monitoring their resource usage (CPU, memory, disk, network) and reporting these to the ResourceManager.
• JobHistoryServer: It maintains information about MapReduce jobs after the Application Master terminates.

Hadoop HDFS Interview Questions

6. Compare HDFS with Network Attached Storage (NAS).

In this question, first explain NAS and HDFS, and then compare their features as follows:

• Network-attached storage (NAS) is a file-level computer data storage server connected to a computer network providing data access to a heterogeneous group of clients. NAS can either be a hardware or software which provides services for storing and accessing files. Whereas Hadoop Distributed File System (HDFS) is a distributed filesystem to store data using commodity hardware.
• In HDFS Data Blocks are distributed across all the machines in a cluster. Whereas in NAS data is stored on a dedicated hardware.
• HDFS is designed to work with MapReduce paradigm, where computation is moved to the data. NAS is not suitable for MapReduce since data is stored separately from the computations.
• HDFS uses commodity hardware which is cost-effective, whereas a NAS is a high-end storage devices which includes high cost.

7. List the difference between Hadoop 1 and Hadoop 2.

This is an important question and while answering this question, we have to mainly focus on two points i.e. Passive NameNode and YARN architecture.

• In Hadoop 1.x, “NameNode” is the single point of failure. In Hadoop 2.x, we have Active and Passive “NameNodes”. If the active “NameNode” fails, the passive “NameNode” takes charge. Because of this, high availability can be achieved in Hadoop 2.x.
• Also, in Hadoop 2.x, YARN provides a central resource manager. With YARN, you can now run multiple applications in Hadoop, all sharing a common resource. MRV2 is a particular type of distributed application that runs the MapReduce framework on top of YARN. Other tools can also perform data processing via YARN, which was a problem in Hadoop 1.x.

8. What are active and passive “NameNodes”? 

In HA (High Availability) architecture, we have two NameNodes – Active “NameNode” and Passive “NameNode”.

• Active “NameNode” is the “NameNode” which works and runs in the cluster.
• Passive “NameNode” is a standby “NameNode”, which has similar data as active “NameNode”.

When the active “NameNode” fails, the passive “NameNode” replaces the active “NameNode” in the cluster. Hence, the cluster is never without a “NameNode” and so it never fails.

9. Why does one remove or add nodes in a Hadoop cluster frequently?

One of the most attractive features of the Hadoop framework is its utilization of commodity hardware. However, this leads to frequent “DataNode” crashes in a Hadoop cluster. Another striking feature of Hadoop Framework is the ease of scale in accordance with the rapid growth in data volume. Because of these two reasons, one of the most common task of a Hadoop administrator is to commission (Add) and decommission (Remove) “Data Nodes” in a Hadoop Cluster.

Read this blog to get a detailed understanding on commissioning and decommissioning nodes in a Hadoop cluster.

10. What happens when two clients try to access the same file in the HDFS?

HDFS supports exclusive writes only.

When the first client contacts the “NameNode” to open the file for writing, the “NameNode” grants a lease to the client to create this file. When the second client tries to open the same file for writing, the “NameNode” will notice that the lease for the file is already granted to another client, and will reject the open request for the second client.

11. How does NameNode tackle DataNode failures?

NameNode periodically receives a Heartbeat (signal) from each of the DataNode in the cluster, which implies DataNode is functioning properly.

A block report contains a list of all the blocks on a DataNode. If a DataNode fails to send a heartbeat message, after a specific period of time it is marked dead.

The NameNode replicates the blocks of dead node to another DataNode using the replicas created earlier.

12. What will you do when NameNode is down?

The NameNode recovery process involves the following steps to make the Hadoop cluster up and running:

1. Use the file system metadata replica (FsImage) to start a new NameNode. 
2. Then, configure the DataNodes and clients so that they can acknowledge this new NameNode, that is started.
3. Now the new NameNode will start serving the client after it has completed loading the last checkpoint FsImage (for metadata information) and received enough block reports from the DataNodes. 

Whereas, on large Hadoop clusters this NameNode recovery process may consume a lot of time and this becomes even a greater challenge in the case of the routine maintenance. Therefore, we have HDFS High Availability Architecture which is covered in the HA architecture blog.

13. What is a checkpoint?

In brief, “Checkpointing” is a process that takes an FsImage, edit log and compacts them into a new FsImage. Thus, instead of replaying an edit log, the NameNode can load the final in-memory state directly from the FsImage. This is a far more efficient operation and reduces NameNode startup time. Checkpointing is performed by Secondary NameNode. 

14. How is HDFS fault tolerant? 

When data is stored over HDFS, NameNode replicates the data to several DataNode. The default replication factor is 3. You can change the configuration factor as per your need. If a DataNode goes down, the NameNode will automatically copy the data to another node from the replicas and make the data available. This provides fault tolerance in HDFS.

15. Can NameNode and DataNode be a commodity hardware? 

The smart answer to this question would be, DataNodes are commodity hardware like personal computers and laptops as it stores data and are required in a large number. But from your experience, you can tell that, NameNode is the master node and it stores metadata about all the blocks stored in HDFS. It requires high memory (RAM) space, so NameNode needs to be a high-end machine with good memory space.

16. Why do we use HDFS for applications having large data sets and not when there are a lot of small files? 

HDFS is more suitable for large amounts of data sets in a single file as compared to small amount of data spread across multiple files. As you know, the NameNode stores the metadata information regarding the file system in the RAM. Therefore, the amount of memory produces a limit to the number of files in my HDFS file system. In other words, too many files will lead to the generation of too much metadata. And, storing these metadata in the RAM will become a challenge. As a thumb rule, metadata for a file, block or directory takes 150 bytes. 

17. How do you define “block” in HDFS? What is the default block size in Hadoop 1 and in Hadoop 2? Can it be changed? 

Blocks are the nothing but the smallest continuous location on your hard drive where data is stored. HDFS stores each as blocks, and distribute it across the Hadoop cluster. Files in HDFS are broken down into block-sized chunks, which are stored as independent units.

• Hadoop 1 default block size: 64 MB
• Hadoop 2 default block size:  128 MB

Yes, blocks can be configured. The dfs.block.size parameter can be used in the hdfs-site.xml file to set the size of a block in a Hadoop environment.

18. What does ‘jps’ command do? 

The ‘jps’ command helps us to check if the Hadoop daemons are running or not. It shows all the Hadoop daemons i.e namenode, datanode, resourcemanager, nodemanager etc. that are running on the machine.

19. How do you define “Rack Awareness” in Hadoop?

Rack Awareness is the algorithm in which the “NameNode” decides how blocks and their replicas are placed, based on rack definitions to minimize network traffic between “DataNodes” within the same rack. Let’s say we consider replication factor 3 (default), the policy is that “for every block of data, two copies will exist in one rack, third copy in a different rack”. This rule is known as the “Replica Placement Policy”.

To know rack awareness in more detail, refer to the HDFS architecture blog. 

20. What is “speculative execution” in Hadoop? 

If a node appears to be executing a task slower, the master node can redundantly execute another instance of the same task on another node. Then, the task which finishes first will be accepted and the other one is killed. This process is called “speculative execution”.

21. How can I restart “NameNode” or all the daemons in Hadoop? 

This question can have two answers, we will discuss both the answers. We can restart NameNode by following methods:

1. You can stop the NameNode individually using. /sbin /hadoop-daemon.sh stop namenode command and then start the NameNode using. /sbin/hadoop-daemon.sh start namenode command.
2. To stop and start all the daemons, use. /sbin/stop-all.sh and then use ./sbin/start-all.sh command which will stop all the daemons first and then start all the daemons.

These script files reside in the sbin directory inside the Hadoop directory.

22. What is the difference between an “HDFS Block” and an “Input Split”?

The “HDFS Block” is the physical division of the data while “Input Split” is the logical division of the data. HDFS divides data in blocks for storing the blocks together, whereas for processing, MapReduce divides the data into the input split and assign it to mapper function.

23. Name the three modes in which Hadoop can run.

The three modes in which Hadoop can run are as follows:

1. Standalone (local) mode: This is the default mode if we don’t configure anything. In this mode, all the components of Hadoop, such NameNode, DataNode, ResourceManager, and NodeManager, run as a single Java process. This uses the local filesystem.
2. Pseudo-distributed mode: A single-node Hadoop deployment is considered as running Hadoop system in pseudo-distributed mode. In this mode, all the Hadoop services, including both the master and the slave services, were executed on a single compute node.
3. Fully distributed mode: A Hadoop deployments in which the Hadoop master and slave services run on separate nodes, are stated as fully distributed mode.

Hadoop MapReduce Interview Questions

24. What is “MapReduce”? What is the syntax to run a “MapReduce” program? 

It is a framework/a programming model that is used for processing large data sets over a cluster of computers using parallel programming. The syntax to run a MapReduce program is hadoop_jar_file.jar /input_path /output_path.

If you have any doubt in MapReduce or want to revise your concepts you can refer this MapReduce tutorial.

25. What are the main configuration parameters in a “MapReduce” program?

The main configuration parameters which users need to specify in “MapReduce” framework are:

• Job’s input locations in the distributed file system
• Job’s output location in the distributed file system
• Input format of data
• Output format of data
• Class containing the map function
• Class containing the reduce function
• JAR file containing the mapper, reducer and driver classes

26. State the reason why we can’t perform “aggregation” (addition) in mapper? Why do we need the “reducer” for this?

This answer includes many points, so we will go through them sequentially.

• We cannot perform “aggregation” (addition) in mapper because sorting does not occur in the “mapper” function. Sorting occurs only on the reducer side and without sorting aggregation cannot be done.
• During “aggregation”, we need the output of all the mapper functions which may not be possible to collect in the map phase as mappers may be running on the different machine where the data blocks are stored.
• And lastly, if we try to aggregate data at mapper, it requires communication between all mapper functions which may be running on different machines. So, it will consume high network bandwidth and can cause network bottlenecking.

27. What is the purpose of “RecordReader” in Hadoop?

The “InputSplit” defines a slice of work, but does not describe how to access it. The “RecordReader” class loads the data from its source and converts it into (key, value) pairs suitable for reading by the “Mapper” task. The “RecordReader” instance is defined by the “Input Format”.

28. Explain “Distributed Cache” in a “MapReduce Framework”.

Distributed Cache can be explained as, a facility provided by the MapReduce framework to cache files needed by applications. Once you have cached a file for your job, Hadoop framework will make it available on each and every data nodes where you map/reduce tasks are running. Then you can access the cache file as a local file in your Mapper or Reducer job.

29. How do “reducers” communicate with each other? 

This is a tricky question. The “MapReduce” programming model does not allow “reducers” to communicate with each other. “Reducers” run in isolation.

30. What does a “MapReduce Partitioner” do?

A “MapReduce Partitioner” makes sure that all the values of a single key go to the same “reducer”, thus allowing even distribution of the map output over the “reducers”. It redirects the “mapper” output to the “reducer” by determining which “reducer” is responsible for the particular key.

31. How will you write a custom partitioner?

Custom partitioner for a Hadoop job can be written easily by following the below steps:

• Create a new class that extends Partitioner Class
• Override method – getPartition, in the wrapper that runs in the MapReduce.
• Add the custom partitioner to the job by using method set Partitioner or add the custom partitioner to the job as a config file.

32. What is a “Combiner”? 

A “Combiner” is a mini “reducer” that performs the local “reduce” task. It receives the input from the “mapper” on a particular “node” and sends the output to the “reducer”. “Combiners” help in enhancing the efficiency of “MapReduce” by reducing the quantum of data that is required to be sent to the “reducers”.

33. What do you know about “SequenceFileInputFormat”?

“SequenceFileInputFormat” is an input format for reading within sequence files. It is a specific compressed binary file format which is optimized for passing the data between the outputs of one “MapReduce” job to the input of some other “MapReduce” job.

Sequence files can be generated as the output of other MapReduce tasks and are an efficient intermediate representation for data that is passing from one MapReduce job to another.

Apache Pig Interview Questions

34. What are the benefits of Apache Pig over MapReduce? 

Apache Pig is a platform, used to analyze large data sets representing them as data flows developed by Yahoo. It is designed to provide an abstraction over MapReduce, reducing the complexities of writing a MapReduce program.

• Pig Latin is a high-level data flow language, whereas MapReduce is a low-level data processing paradigm.
• Without writing complex Java implementations in MapReduce, programmers can achieve the same implementations very easily using Pig Latin.
• Apache Pig reduces the length of the code by approx 20 times (according to Yahoo). Hence, this reduces the development period by almost 16 times.
• Pig provides many built-in operators to support data operations like joins, filters, ordering, sorting etc. Whereas to perform the same function in MapReduce is a humongous task.
• Performing a Join operation in Apache Pig is simple. Whereas it is difficult in MapReduce to perform a Join operation between the data sets, as it requires multiple MapReduce tasks to be executed sequentially to fulfill the job.
• In addition, pig also provides nested data types like tuples, bags, and maps that are missing from MapReduce.

35. What are the different data types in Pig Latin?

Pig Latin can handle both atomic data types like int, float, long, double etc. and complex data types like tuple, bag and map.

Atomic data types: Atomic or scalar data types are the basic data types which are used in all the languages like string, int, float, long, double, char[], byte[].

Complex Data Types: Complex data types are Tuple, Map and Bag.

To know more about these data types, you can go through our Pig tutorial blog.

36. What are the different relational operations in “Pig Latin” you worked with?

Different relational operators are:

1. for each
2. order by
3. filters
4. group
5. distinct
6. join
7. limit

37. What is a UDF?

If some functions are unavailable in built-in operators, we can programmatically create User Defined Functions (UDF) to bring those functionalities using other languages like Java, Python, Ruby, etc. and embed it in Script file.

38. What is “SerDe” in “Hive”?

Apache Hive is a data warehouse system built on top of Hadoop and is used for analyzing structured and semi-structured data developed by Facebook. Hive abstracts the complexity of Hadoop MapReduce.

The “SerDe” interface allows you to instruct “Hive” about how a record should be processed. A “SerDe” is a combination of a “Serializer” and a “Deserializer”. “Hive” uses “SerDe” (and “FileFormat”) to read and write the table’s row.

To know more about Apache Hive, you can go through this Hive tutorial blog.

39. Can the default “Hive Metastore” be used by multiple users (processes) at the same time?

“Derby database” is the default “Hive Metastore”. Multiple users (processes) cannot access it at the same time. It is mainly used to perform unit tests.

40. What is the default location where “Hive” stores table data?

The default location where Hive stores table data is inside HDFS in /user/hive/warehouse.

Apache HBase Interview Questions

41. What is Apache HBase?

HBase is an open source, multidimensional, distributed, scalable and a NoSQL database written in Java. HBase runs on top of HDFS (Hadoop Distributed File System) and provides BigTable (Google) like capabilities to Hadoop. It is designed to provide a fault-tolerant way of storing the large collection of sparse data sets. HBase achieves high throughput and low latency by providing faster Read/Write Access on huge datasets.

To know more about HBase you can go through our HBase tutorial blog.

42. What are the components of Apache HBase?

HBase has three major components, i.e. HMaster Server, HBase RegionServer and Zookeeper.

• Region Server: A table can be divided into several regions. A group of regions is served to the clients by a Region Server.
• HMaster: It coordinates and manages the Region Server (similar as NameNode manages DataNode in HDFS).
• ZooKeeper: Zookeeper acts like as a coordinator inside HBase distributed environment. It helps in maintaining server state inside the cluster by communicating through sessions.

To know more, you can go through this HBase architecture blog.

43. What are the components of Region Server?

The components of a Region Server are:

• WAL: Write Ahead Log (WAL) is a file attached to every Region Server inside the distributed environment. The WAL stores the new data that hasn’t been persisted or committed to the permanent storage.
• Block Cache: Block Cache resides in the top of Region Server. It stores the frequently read data in the memory.
• MemStore: It is the write cache. It stores all the incoming data before committing it to the disk or permanent memory. There is one MemStore for each column family in a region.
• HFile: HFile is stored in HDFS. It stores the actual cells on the disk.

44. Explain “WAL” in HBase?

Write Ahead Log (WAL) is a file attached to every Region Server inside the distributed environment. The WAL stores the new data that hasn’t been persisted or committed to the permanent storage. It is used in case of failure to recover the data sets.

45. Mention the differences between “HBase” and “Relational Databases”?

HBase is an open source, multidimensional, distributed, scalable and a NoSQL database written in Java. HBase runs on top of HDFS and provides BigTable like capabilities to Hadoop. Let us see the differences between HBase and relational database.

Apache Spark Interview Questions

46. What is Apache Spark?

The answer to this question is, Apache Spark is a framework for real-time data analytics in a distributed computing environment. It executes in-memory computations to increase the speed of data processing.

It is 100x faster than MapReduce for large-scale data processing by exploiting in-memory computations and other optimizations.

47. Can you build “Spark” with any particular Hadoop version?

Yes, one can build “Spark” for a specific Hadoop version. Check out this blog to learn more about building YARN and HIVE on Spark. 

48. Define RDD.

RDD is the acronym for Resilient Distribution Datasets – a fault-tolerant collection of operational elements that run parallel. The partitioned data in RDD are immutable and distributed, which is a key component of Apache Spark.

Oozie & ZooKeeper Interview Questions

49. What is Apache ZooKeeper and Apache Oozie?

Apache ZooKeeper coordinates with various services in a distributed environment. It saves a lot of time by performing synchronization, configuration maintenance, grouping and naming.

Apache Oozie is a scheduler which schedules Hadoop jobs and binds them together as one logical work. There are two kinds of Oozie jobs:

• Oozie Workflow: These are the sequential set of actions to be executed. You can assume it as a relay race. Where each athlete waits for the last one to complete his part.
• Oozie Coordinator: These are the Oozie jobs which are triggered when the data is made available to it. Think of this as the response-stimuli system in our body. In the same manner, as we respond to an external stimulus, an Oozie coordinator responds to the availability of data and it rests otherwise.

50. How do you configure an “Oozie” job in Hadoop?

“Oozie” is integrated with the rest of the Hadoop stack supporting several types of Hadoop jobs such as “Java MapReduce”, “Streaming MapReduce”, “Pig”, “Hive” and “Sqoop”.

To understand “Oozie” in detail and learn how to configure an “Oozie” job, do check out this introduction to Apache Oozie blog.

Feeling overwhelmed with all the questions the interviewer might ask in your Hadoop interview? Now it is time to go through a series of Hadoop interview questions which covers different aspects of the Hadoop framework. It’s never too late to strengthen your basics. Learn Hadoop from industry experts while working with real-life use cases.

Got a question for us? Please mention it in the comments section and we will get back to you.

In this blog post, let’s discuss top Hive commands with examples. These Hive commands are very important to set up the foundation for Hive Certification Training.

What is Hive?

Apache Hive is a Data warehouse system which is built to work on Hadoop. It is used to querying and managing large datasets residing in distributed storage. Before becoming an open source project of Apache Hadoop, Hive was originated in Facebook. It provides a mechanism to project structure onto the data in Hadoop and to query that data using a SQL-like language called HiveQL (HQL).

Hive is used because the tables in Hive are similar to tables in a relational database. If you are familiar with SQL, it’s a cakewalk. Many users can simultaneously query the data using Hive-QL.

What is HQL?

Hive defines a simple SQL-like query language to querying and managing large datasets called Hive-QL ( HQL ). It’s easy to use if you’re familiar with SQL Language. Hive allows programmers who are familiar with the language to write the custom MapReduce framework to perform more sophisticated analysis.

Uses of Hive:

1. The Apache Hive distributed storage.

2. Hive provides tools to enable easy data extract/transform/load (ETL)

3. It provides the structure on a variety of data formats.

4. By using Hive, we can access files stored in Hadoop Distributed File System (HDFS is used to querying and managing large datasets residing in) or in other data storage systems such as Apache HBase.

Limitations of Hive:

• Hive is not designed for Online transaction processing (OLTP ), it is only used for the Online Analytical Processing.

• Hive supports overwriting or apprehending data, but not updates and deletes.

• In Hive, sub queries are not supported.

Why Hive is used inspite of Pig?

The following are the reasons why Hive is used in spite of Pig’s availability:

• Hive-QL is a declarative language line SQL, PigLatin is a data flow language.
• Pig: a data-flow language and environment for exploring very large datasets.
• Hive: a distributed data warehouse.

Components of Hive:

Metastore :

Hive stores the schema of the Hive tables in a Hive Metastore. Metastore is used to hold all the information about the tables and partitions that are in the warehouse. By default, the metastore is run in the same process as the Hive service and the default Metastore is DerBy Database.

SerDe :

Serializer, Deserializer gives instructions to hive on how to process a record.

Hive Commands :

Data Definition Language (DDL )

DDL statements are used to build and modify the tables and other objects in the database.

Example :

CREATE, DROP, TRUNCATE, ALTER, SHOW, DESCRIBE Statements.

Go to Hive shell by giving the command sudo hive and enter the command ‘create database<data base name>’ to create the new database in the Hive.

To list out the databases in Hive warehouse, enter the command ‘show databases’.

The database creates in a default location of the Hive warehouse. In Cloudera, Hive database store in a /user/hive/warehouse.

The command to use the database is USE <data base name>

Copy the input data to HDFS from local by using the copy From Local command.

When we create a table in hive, it creates in the default location of the hive warehouse. – “/user/hive/warehouse”, after creation of the table we can move the data from HDFS to hive table.

The following command creates a table with in location of “/user/hive/warehouse/retail.db”

Note : retail.db is the database created in the Hive warehouse.

Describe provides information about the schema of the table.

Data Manipulation Language (DML )

DML statements are used to retrieve, store, modify, delete, insert and update data in the database.

Example :

LOAD, INSERT Statements.

Syntax :

LOAD data <LOCAL> inpath <file path> into table [tablename]

The Load operation is used to move the data into corresponding Hive table. If the keyword local is specified, then in the load command will give the local file system path. If the keyword local is not specified we have to use the HDFS path of the file.

Here are some examples for the LOAD data LOCAL command

After loading the data into the Hive table we can apply the Data Manipulation Statements or aggregate functions retrieve the data.

Example to count number of records:

Count aggregate function is used count the total number of the records in a table.

‘create external’ Table :

The create external keyword is used to create a table and provides a location where the table will create, so that Hive does not use a default location for this table. An EXTERNAL table points to any HDFS location for its storage, rather than default storage.

Insert Command:

The insert command is used to load the data Hive table. Inserts can be done to a table or a partition.

• INSERT OVERWRITE is used to overwrite the existing data in the table or partition.

• INSERT INTO is used to append the data into existing data in a table. (Note: INSERT INTO syntax is work from the version 0.8)

Example for ‘Partitioned By’ and ‘Clustered By’ Command :

‘Partitioned by‘ is used to divided the table into the Partition and can be divided in to buckets by using the ‘Clustered By‘ command.

When we insert the data Hive throwing errors, the dynamic partition mode is strict and dynamic partition not enabled (by Jeff at dresshead website). So we need to set the following parameters in Hive shell.

set hive.exec.dynamic.partition=true;

To enable dynamic partitions, by default, it’s false

set hive.exec.dynamic.partition.mode=nonstrict;

Partition is done by the category and can be divided in to buckets by using the ‘Clustered By’ command.

The ‘Drop Table’ statement deletes the data and metadata for a table. In the case of external tables, only the metadata is deleted.

The ‘Drop Table’ statement deletes the data and metadata for a table. In the case of external tables, only the metadata is deleted.

Load data local inpath ‘aru.txt’ into table tablename and then we check employee1 table by using Select * from table name command

To count the number of records in table by using Select count(*) from txnrecords;

Aggregation :

Select count (DISTINCT category) from tablename;

This command will count the different category of ‘cate’ table. Here there are 3 different categories.

Suppose there is another table cate where f1 is field name of category.

Grouping :

Group command is used to group the result-set by one or more columns.

Select category, sum( amount) from txt records group by category

It calculates the amount of same category.

The result one table is stored in to another table.

Create table newtablename as select * from oldtablename;

Join Command :

Here one more table is created in the name ‘mailid’

Join Operation:

A Join operation is performed to combining fields from two tables by using values common to each.

Left Outer Join:

The result of a left outer join (or simply left join) for tables A and B always contains all records of the “left” table (A), even if the join-condition does not find any matching record in the “right” table (B).

Right Outer Join:

A right outer join (or right join) closely resembles a left outer join, except with the treatment of the tables reversed. Every row from the “right” table (B) will appear in the joined table at least once.

Full Join:

The joined table will contain all records from both tables, and fill in NULLs for missing matches on either side.

Once done with hive we can use quit command to exit from the hive shell.

Hive is just a part of the big puzzle called Big Data and Hadoop. Hadoop is much more than just Hive. Click below to see what other skills you should master in Hadoop.

Got a question for us? Please mention it in the comments section and we will get back to you.

Related Posts:

7 Ways Big Data Training Can Change Your Organization

Get Started with Big Data & Hadoop

Hive Data Models

If you are an aspiring front end developer and preparing for interviews, then this blog is for you. This blog on Top 50 React Interview Questions is the perfect guide for you to learn all the concepts required to clear a React interview. But before starting with the React Interview Questions, let’s take a quick look at React’s demand and status in the market.

Slowly and steadily, the JavaScript tools are firming their roots in the marketplace and the demand for React certification is increasing exponentially. Selecting the right technology for developing an application or website is becoming more challenging. Among all, React is considered as the fastest growing Javascript framework.

As of today, there are about 1,000 contributors on Github. Unique features like Virtual DOM and reusable components grab the attention of front end developers. Despite being just a library for ‘View’ in MVC (Model-View-Controller), it’s giving strong competition to full-blown frameworks like Angular, Meteor, Vue, etc. Check out the belo2w graph which shows the trend of popular JS frameworks:

So, here are the Top 50 React Interview Questions and Answers which are most likely to be asked by the interviewer. For your ease of access, I have categorized the React interview questions namely:

• General React Interview Questions
• React Component Interview Questions
• React Redux Interview Questions
• React Router Interview Questions

1.  Differentiate between Real DOM and Virtual DOM.

2. What is React?

• React is a front-end JavaScript library developed by Facebook in 2011.
• It follows the component based approach which helps in building reusable UI components.
• It is used for developing complex and interactive web and mobile UI.
• Even though it was open-sourced only in 2015, it has one of the largest communities supporting it.

3. What are the features of React? 

Major features of React are listed below:

1. It uses the virtual DOM instead of the real DOM.
2. It uses server-side rendering.
3. It follows uni-directional data flow or data binding.

4. List some of the major advantages of React.

Some of the major advantages of React are:

1. It increases the application’s performance
2. It can be conveniently used on the client as well as server side
3. Because of JSX, code’s readability increases
4. React is easy to integrate with other frameworks like Meteor, Angular, etc
5. Using React, writing UI test cases become extremely easy

5. What are the limitations of React?

Limitations of React are listed below:

1. React is just a library, not a full-blown framework
2. Its library is very large and takes time to understand
3. It can be little difficult for the novice programmers to understand
4. Coding gets complex as it uses inline templating and JSX

React Interview Questions and Answers | Edureka

6. What is JSX?

JSX is a shorthand for JavaScript XML. This is a type of file used by React which utilizes the expressiveness of JavaScript along with HTML like template syntax. This makes the HTML file really easy to understand. This file makes applications robust and boosts its performance. Below is an example of JSX:

render(){
    return(        
         


<div>
            


<h1> Hello World from Edureka!!</h1>



         </div>



    );
}

7. What do you understand by Virtual DOM? Explain its working.

A virtual DOM is a lightweight JavaScript object which originally is just the copy of the real DOM. It is a node tree that lists the elements, their attributes and content as Objects and their properties. React’s render function creates a node tree out of the React components. It then updates this tree in response to the mutations in the data model which is caused by various actions done by the user or by the system.
This Virtual DOM works in three simple steps.

1. Whenever any underlying data changes, the entire UI is re-rendered in Virtual DOM representation.
2. Then the difference between the previous DOM representation and the new one is calculated.
3. Once the calculations are done, the real DOM will be updated with only the things that have actually changed. 

8. Why can’t browsers read JSX?

Browsers can only read JavaScript objects but JSX in not a regular JavaScript object. Thus to enable a browser to read JSX, first, we need to transform JSX file into a JavaScript object using JSX transformers like Babel and then pass it to the browser.

9. How different is React’s ES6 syntax when compared to ES5?

Syntax has changed from ES5 to ES6 in following aspects:

1. require vs import

   // ES5
   var React = require('react');
   
   // ES6
   import React from 'react';

2. export vs exports
   

   // ES5
   module.exports = Component;
   
   // ES6
   export default Component;

3. component and function

   // ES5
   var MyComponent = React.createClass({
       render: function() {
           return 
   
   
   <h3>Hello Edureka!</h3>
   
   
   
   ;
       }
   });
   
   // ES6
   class MyComponent extends React.Component {
       render() {
           return 
   
   
   <h3>Hello Edureka!</h3>
   
   
   
   ;
       }
   }

4. props
   

   // ES5
   var App = React.createClass({
       propTypes: { name: React.PropTypes.string },
       render: function() {
           return 
   
   
   <h3>Hello, {this.props.name}!</h3>
   
   
   
   ;
       }
   });
   
   // ES6
   class App extends React.Component {
       render() {
           return 
   
   
   <h3>Hello, {this.props.name}!</h3>
   
   
   
   ;
       }
   }

5. state
   

   // ES5
   var App = React.createClass({
       getInitialState: function() {
           return { name: 'world' };
       },
       render: function() {
           return 
   
   
   <h3>Hello, {this.state.name}!</h3>
   
   
   
   ;
       }
   });
   
   // ES6
   class App extends React.Component {
       constructor() {
           super();
           this.state = { name: 'world' };
       }
       render() {
           return 
   
   
   <h3>Hello, {this.state.name}!</h3>
   
   
   
   ;
       }
   }

10. How is React different from Angular?

11. What do you understand from “In React, everything is a component.”

Components are the building blocks of a React application’s UI. These components split up the entire UI into small independent and reusable pieces. Then it renders each of these components independent of each other without affecting the rest of the UI.

12. Explain the purpose of render() in React.

Each React component must have a render() mandatorily. It returns a single React element which is the representation of the native DOM component. If more than one HTML element needs to be rendered, then they must be grouped together inside one enclosing tag such as <form>, <group>,<div> etc. This function must be kept pure i.e., it must return the same result each time it is invoked.

13. How can you embed two or more components into one?

We can embed components into one in the following way:

class MyComponent extends React.Component{
    render(){
        return(          
            


<div>
              
                


<h1>Hello</h1>



                <Header/>
            </div>



        );
    }
}
class Header extends React.Component{
    render(){
        return 


<h1>Header Component</h1>



   
   };
}
ReactDOM.render(
    <MyComponent/>, document.getElementById('content')
);

14. What is Props?

Props is the shorthand for Properties in React. They are read-only components which must be kept pure i.e. immutable. They are always passed down from the parent to the child components throughout the application. A child component can never send a prop back to the parent component. This help in maintaining the unidirectional data flow and are generally used to render the dynamically generated data.

15. What is a state in React and how is it used?

States are the heart of React components. States are the source of data and must be kept as simple as possible. Basically, states are the objects which determine components rendering and behavior. They are mutable unlike the props and create dynamic and interactive components. They are accessed via this.state().

16. Differentiate between states and props.

17. How can you update the state of a component?

State of a component can be updated using this.setState().

class MyComponent extends React.Component {
    constructor() {
        super();
        this.state = {
            name: 'Maxx',
            id: '101'
        }
    }
    render()
        {
            setTimeout(()=>{this.setState({name:'Jaeha', id:'222'})},2000)
            return (              
                   


<div>
                  
                     


<h1>Hello {this.state.name}</h1>



                
                     


<h2>Your Id is {this.state.id}</h2>



                   </div>



            );
        }
    }
ReactDOM.render(
    <MyComponent/>, document.getElementById('content')
);

18. What is arrow function in React? How is it used?

Arrow functions are more of brief syntax for writing the function expression. They are also called ‘fat arrow‘ (=>) the functions. These functions allow to bind the context of the components properly since in ES6 auto binding is not available by default. Arrow functions are mostly useful while working with the higher order functions.

//General way
render() {    
    return(
        <MyInput onChange={this.handleChange.bind(this) } />
    );
}
//With Arrow Function
render() {  
    return(
        <MyInput onChange={ (e) => this.handleOnChange(e) } />
    );
}

19. Differentiate between stateful and stateless components.

20. What are the different phases of React component’s lifecycle?

There are three different phases of React component’s lifecycle:

1. Initial Rendering Phase: This is the phase when the component is about to start its life journey and make its way to the DOM.
2. Updating Phase: Once the component gets added to the DOM, it can potentially update and re-render only when a prop or state change occurs. That happens only in this phase.
3. Unmounting Phase: This is the final phase of a component’s life cycle in which the component is destroyed and removed from the DOM.

21. Explain the lifecycle methods of React components in detail.

Some of the most important lifecycle methods are:

1. componentWillMount() – Executed just before rendering takes place both on the client as well as server-side.
2. componentDidMount() – Executed on the client side only after the first render.
3. componentWillReceiveProps() – Invoked as soon as the props are received from the parent class and before another render is called.
4. shouldComponentUpdate() – Returns true or false value based on certain conditions. If you want your component to update, return true else return false. By default, it returns false.
5. componentWillUpdate() – Called just before rendering takes place in the DOM.
6. componentDidUpdate() – Called immediately after rendering takes place.
7. componentWillUnmount() – Called after the component is unmounted from the DOM. It is used to clear up the memory spaces.

22. What is an event in React?

In React, events are the triggered reactions to specific actions like mouse hover, mouse click, key press, etc. Handling these events are similar to handling events in DOM elements. But there are some syntactical differences like:

1. Events are named using camel case instead of just using the lowercase.
2. Events are passed as functions instead of strings.

The event argument contains a set of properties, which are specific to an event. Each event type contains its own properties and behavior which can be accessed via its event handler only.

23. How do you create an event in React?

class Display extends React.Component({    
    show(evt) {
        // code   
    },   
    render() {      
        // Render the div with an onClick prop (value is a function)        
        return (            
          


<div onClick={this.show}>Click Me!</div>



        );    
    }
});

24. What are synthetic events in React?

Synthetic events are the objects which act as a cross-browser wrapper around the browser’s native event. They combine the behavior of different browsers into one API. This is done to make sure that the events show consistent properties across different browsers.

25. What do you understand by refs in React?

Refs is the short hand for References in React. It is an attribute which helps to store a reference to a particular React element or component, which will be returned by the components render configuration function. It is used to return references to a particular element or component returned by render(). They come in handy when we need DOM measurements or to add methods to the components.

class ReferenceDemo extends React.Component{
     display() {
         const name = this.inputDemo.value;
         document.getElementById('disp').innerHTML = name;
     }
render() {
    return(        
         


<div>
            Name: <input type="text" ref={input => this.inputDemo = input} />
            <button name="Click" onClick={this.display}>Click</button>            
            


<h2>Hello <span id="disp"></span> !!!</h2>



        </div>



    );
   }
 }

26. List some of the cases when you should use Refs.

Following are the cases when refs should be used:

• When you need to manage focus, select text or media playback
• To trigger imperative animations
• Integrate with third-party DOM libraries

27. How do you modularize code in React?

We can modularize code by using the export and import properties. They help in writing the components separately in different files.

//ChildComponent.jsx
export default class ChildComponent extends React.Component {
    render() {
        return(           
             


<div>
             
                


<h1>This is a child component</h1>



            </div>



        );
    }
}

//ParentComponent.jsx
import ChildComponent from './childcomponent.js';
class ParentComponent extends React.Component {    
    render() {        
        return(           
            


<div>               
                <App />          
            </div>



       
        );  
    }
}

28. How are forms created in React?

React forms are similar to HTML forms. But in React, the state is contained in the state property of the component and is only updated via setState(). Thus the elements can’t directly update their state and their submission is handled by a JavaScript function. This function has full access to the data that is entered by the user into a form.

handleSubmit(event) {
    alert('A name was submitted: ' + this.state.value);
    event.preventDefault();
}

render() {
    return (        
        


<form onSubmit={this.handleSubmit}>
            <label>
                Name:
                <input type="text" value={this.state.value} onChange={this.handleSubmit} />
            </label>
            <input type="submit" value="Submit" />
        </form>



    );
}

29. What do you know about controlled and uncontrolled components?

30. What are Higher Order Components(HOC)?

Higher Order Component is an advanced way of reusing the component logic. Basically, it’s a pattern that is derived from React’s compositional nature. HOC are custom components which wrap another component within it. They can accept any dynamically provided child component but they won’t modify or copy any behavior from their input components. You can say that HOC are ‘pure’ components.

31. What can you do with HOC?

HOC can be used for many tasks like:

• Code reuse, logic and bootstrap abstraction
• Render High jacking
• State abstraction and manipulation
• Props manipulation

32. What are Pure Components?

Pure components are the simplest and fastest components which can be written. They can replace any component which only has a render(). These components enhance the simplicity of the code and performance of the application.

33. What is the significance of keys in React?

Keys are used for identifying unique Virtual DOM Elements with their corresponding data driving the UI. They help React to optimize the rendering by recycling all the existing elements in the DOM. These keys must be a unique number or string, using which React just reorders the elements instead of re-rendering them. This leads to increase in application’s performance.

34. What were the major problems with MVC framework?

Following are some of the major problems with MVC framework:

• DOM manipulation was very expensive
• Applications were slow and inefficient
• There was huge memory wastage
• Because of circular dependencies, a complicated model was created around models and views

35. Explain Flux.

Flux is an architectural pattern which enforces the uni-directional data flow. It controls derived data and enables communication between multiple components using a central Store which has authority for all data. Any update in data throughout the application must occur here only. Flux provides stability to the application and reduces run-time errors.

36. What is Redux?

Redux is one of the hottest libraries for front-end development in today’s marketplace. It is a predictable state container for JavaScript applications and is used for the entire applications state management. Applications developed with Redux are easy to test and can run in different environments showing consistent behavior.

37. What are the three principles that Redux follows?

1. Single source of truth: The state of the entire application is stored in an object/ state tree within a single store. The single state tree makes it easier to keep track of changes over time and debug or inspect the application.
2. State is read-only: The only way to change the state is to trigger an action. An action is a plain JS object describing the change. Just like state is the minimal representation of data, the action is the minimal representation of the change to that data. 
3. Changes are made with pure functions: In order to specify how the state tree is transformed by actions, you need pure functions. Pure functions are those whose return value depends solely on the values of their arguments.

38. What do you understand by “Single source of truth”?

Redux uses ‘Store’ for storing the application’s entire state at one place. So all the component’s state are stored in the Store and they receive updates from the Store itself. The single state tree makes it easier to keep track of changes over time and debug or inspect the application.

39. List down the components of Redux.

Redux is composed of the following components:

1. Action – It’s an object that describes what happened.
2. Reducer –  It is a place to determine how the state will change.
3. Store – State/ Object tree of the entire application is saved in the Store.
4. View – Simply displays the data provided by the Store.

40. Show how the data flows through Redux?

41. How are Actions defined in Redux?

Actions in React must have a type property that indicates the type of ACTION being performed. They must be defined as a String constant and you can add more properties to it as well. In Redux, actions are created using the functions called Action Creators. Below is an example of Action and Action Creator:

function addTodo(text) {
       return {
                type: ADD_TODO,    
                 text    
    }
}

42. Explain the role of Reducer.

Reducers are pure functions which specify how the application’s state changes in response to an ACTION. Reducers work by taking in the previous state and action, and then it returns a new state. It determines what sort of update needs to be done based on the type of the action, and then returns new values. It returns the previous state as it is, if no work needs to be done.

43. What is the significance of Store in Redux?

A store is a JavaScript object which can hold the application’s state and provide a few helper methods to access the state, dispatch actions and register listeners. The entire state/ object tree of an application is saved in a single store. As a result of this, Redux is very simple and predictable. We can pass middleware to the store to handle the processing of data as well as to keep a log of various actions that change the state of stores. All the actions return a new state via reducers.

44. How is Redux different from Flux?

45. What are the advantages of Redux?

Advantages of Redux are listed below:

• Predictability of outcome – Since there is always one source of truth, i.e. the store, there is no confusion about how to sync the current state with actions and other parts of the application.
• Maintainability – The code becomes easier to maintain with a predictable outcome and strict structure.
• Server-side rendering – You just need to pass the store created on the server, to the client side. This is very useful for initial render and provides a better user experience as it optimizes the application performance.
• Developer tools – From actions to state changes, developers can track everything going on in the application in real time.
• Community and ecosystem – Redux has a huge community behind it which makes it even more captivating to use. A large community of talented individuals contribute to the betterment of the library and develop various applications with it.
• Ease of testing – Redux’s code is mostly functions which are small, pure and isolated. This makes the code testable and independent.
• Organization – Redux is precise about how code should be organized, this makes the code more consistent and easier when a team works with it.

46. What is React Router?

React Router is a powerful routing library built on top of React, which helps in adding new screens and flows to the application. This keeps the URL in sync with data that’s being displayed on the web page. It maintains a standardized structure and behavior and is used for developing single page web applications. React Router has a simple API.

47. Why is switch keyword used in React Router v4?

Although a <div> is used to encapsulate multiple routes inside the Router. The ‘switch’ keyword is used when you want to display only a single route to be rendered amongst the several defined routes. The <switch> tag when in use matches the typed URL with the defined routes in sequential order. When the first match is found, it renders the specified route. Thereby bypassing the remaining routes.

48. Why do we need a Router in React?

A Router is used to define multiple routes and when a user types a specific URL, if this URL matches the path of any ‘route’ defined inside the router, then the user is redirected to that particular route. So basically, we need to add a Router library to our app that allows creating multiple routes with each leading to us a unique view.

<switch>
    <route exact path=’/’ component={Home}/>
    <route path=’/posts/:id’ component={Newpost}/>
    <route path=’/posts’   component={Post}/>
</switch>

49. List down the advantages of React Router.

Few advantages are:

1. Just like how React is based on components, in React Router v4, the API is ‘All About Components’. A Router can be visualized as a single root component (<BrowserRouter>) in which we enclose the specific child routes (<route>).
2. No need to manually set History value: In React Router v4, all we need to do is wrap our routes within the <BrowserRouter> component.
3. The packages are split: Three packages one each for Web, Native and Core. This supports the compact size of our application. It is easy to switch over based on a similar coding style.

50. How is React Router different from conventional routing?

I hope this set of React Interview Questions and Answers will help you in preparing for your interviews. All the best!

If you want to get trained in React and wish to develop interesting UI’s on your own, then check out the ReactJS with Redux Certification Training by Edureka, a trusted online learning company with a network of more than 250,000 satisfied learners spread across the globe.

Got a question for us? Please mention it in the comments section and we will get back to you.

In this Tableau interview questions blog, I have collected the most frequently asked questions by interviewers. These questions are collected after consulting with top industry experts in the field of Data analytics and visualization. If you want to brush up with the Tableau basics, which I recommend you to do before going ahead with this Tableau Interview Questions, take a look at this blog. 

In case you have attended a Tableau interview in the recent past, do paste those Tableau interview questions in the comments section and we’ll answer them ASAP. You can also comment below if you have any questions in your mind which you might face in your Tableau interview. In the meantime, maximize the data visualization career opportunities that are sure to come your way by taking Tableau online training with Edureka. You can even get a Tableau certification after the course. Click below to know more.

This Tableau Interview questions is divided into the following parts:

• Beginners level
• Intermediate Level
• Expert Level
• Tricky Questions

Let’s begin this Tableau Interview Questions with Beginners level questions first.

Beginners Level Tableau Interview Questions

1. What is the difference between Traditional BI Tools and Tableau?

2. What is Tableau?

• Tableau is a business intelligence software.
• It allows anyone to connect to the respective data.
• Visualizes and creates interactive, shareable dashboards.

3. What are the different Tableau Products and what is the latest version of Tableau?

Here is the Tableau Product family.

(i)Tableau Desktop:

It is a self service business analytics and data visualization that anyone can use. It translates pictures of data into optimized queries. With tableau desktop, you can directly connect to data from your data warehouse for live upto date data analysis. You can also perform queries without writing a single line of code. Import all your data into Tableau’s data engine from multiple sources & integrate altogether by combining multiple views in a interactive dashboard.

(ii)Tableau Server:

It is more of an enterprise level Tableau software. You can publish dashboards with Tableau Desktop and share them throughout the organization with web-based Tableau server. It leverages fast databases through live connections.

(iii)Tableau Online:

This is a hosted version of Tableau server which helps makes business intelligence faster and easier than before. You can publish Tableau dashboards with Tableau Desktop and share them with colleagues.

(iv)Tableau Reader:

It’s a free desktop application that enables you to open and view visualizations that are built in Tableau Desktop. You can filter, drill down data but you cannot edit or perform any kind of interactions.

(v)Tableau Public:

This is a free Tableau software which you can use to make visualizations with but you need to save your workbook or worksheets in the Tableau Server which can be viewed by anyone.

4. What are the different datatypes in Tableau?

Tableau supports the following data-types:

5. What are Measures and Dimensions?

Measures are the numeric metrics or measurable quantities of the data, which can be analyzed by dimension table. Measures are stored in a table that contain foreign keys referring uniquely to the associated dimension tables. The table supports data storage at atomic level and thus, allows more number of records to be inserted at one time. For instance, a Sales table can have product key, customer key, promotion key, items sold, referring to a specific event.

Dimensions are the descriptive attribute values for multiple dimensions of each attribute, defining multiple characteristics. A dimension table ,having reference of a product key form the table, can consist of product name, product type, size, color, description, etc.

6. What is the difference between .twb and .twbx extension?

• A .twb is an xml document which contains all the selections and layout made you have made in your Tableau workbook. It does not contain any data.
• A .twbx is a ‘zipped’ archive containing a .twb and any external files such as extracts and background images.

7. What are the different types of joins in Tableau?

The joins in Tableau are same as SQL joins. Take a look at the diagram below to understand it.

8. How many maximum tables can you join in Tableau?

You can join a maximum of 32 tables in Tableau.

9. What are the different connections you can make with your dataset?

We can either connect live to our data set or extract data onto Tableau.

• Live: Connecting live to a data set leverages its computational processing and storage. New queries will go to the database and will be reflected as new or updated within the data.
• Extract: An extract will make a static snapshot of the data to be used by Tableau’s data engine. The snapshot of the data can be refreshed on a recurring schedule as a whole or incrementally append data. One way to set up these schedules is via the Tableau server.

The benefit of Tableau extract over live connection is that extract can be used anywhere without any connection and you can build your own visualization without connecting to database.

10. What are shelves?

They are Named areas to the left and top of the view. You build views by placing fields onto the shelves. Some shelves are available only when you select certain mark types.

11. What are sets?

Sets are custom fields that define a subset of data based on some conditions. A set can be based on a computed condition, for example, a set may contain customers with sales over a certain threshold. Computed sets update as your data changes. Alternatively, a set can be based on specific data point in your view.

12. What are groups?

A group is a combination of dimension members that make higher level categories. For example, if you are working with a view that shows average test scores by major, you may want to group certain majors together to create major categories.

13. What is a hierarchical field?

A hierarchical field in tableau is used for drilling down data. It means viewing your data in a more granular level.

14. What is Tableau Data Server?

Tableau server acts a middle man between Tableau users and the data. Tableau Data Server allows you to upload and share data extracts, preserve database connections, as well as reuse calculations and field metadata. This means any changes you make to the data-set, calculated fields, parameters, aliases, or definitions, can be saved and shared with others, allowing for a secure, centrally managed and standardized dataset. Additionally, you can leverage your server’s resources to run queries on extracts without having to first transfer them to your local machine.

Intermediate Level Tableau Interview Questions

15. What is Tableau Data Engine?

Tableau Data Engine is a really cool feature in Tableau. Its an analytical database designed to achieve instant query response, predictive performance, integrate seamlessly into existing data infrastructure and is not limited to load entire data sets into memory.

If you work with a large amount of data, it does takes some time to import, create indexes and sort data but after that everything speeds up. Tableau Data Engine is not really in-memory technology. The data is stored in disk after it is imported and the RAM is hardly utilized. 

16. What are the different filters in Tableau and how are they different from each other?

In Tableau, filters are used to restrict the data from database.

The different filters in Tableau are: Quick , Context and Normal/Traditional filter are:

• Normal Filter is used to restrict the data from database based on selected dimension or measure. A Traditional Filter can be created by simply dragging a field onto the ‘Filters’ shelf.
• Quick filter is used to view the filtering options and filter each worksheet on a dashboard while changing the values dynamically (within the range defined) during the run time.
• Context Filter is used to filter the data that is transferred to each individual worksheet. When a worksheet queries the data source, it creates a temporary, flat table that is uses to compute the chart. This temporary table includes all values that are not filtered out by either the Custom SQL or the Context Filter.

17. How to create a calculated field in Tableau?

• Click the drop down to the right of Dimensions on the Data pane and select “Create > Calculated Field” to open the calculation editor.
• Name the new field and create a formula.

Take a look at the example below:

18. What is a dual axis?

Dual Axis is an excellent phenomenon supported by Tableau that helps users view two scales of two measures in the same graph. Many websites like Indeed.com and other make use of dual axis to show the comparison between two measures and their growth rate in a septic set of years. Dual axes let you compare multiple measures at once, having two independent axes layered on top of one another. This is how it looks like:

19. What is the difference between a tree map and heat map?

A heat map can be used for comparing categories with color and size. With heat maps, you can compare two different measures together.

A tree map also does the same except it is considered a very powerful visualization as it can be used for illustrating hierarchical data and part-to-whole relationships.

20. What is disaggregation and aggregation of data?

The process of viewing numeric values or measures at higher and more summarized levels of the data is called aggregation. When you place a measure on a shelf, Tableau automatically aggregates the data, usually by summing it. You can easily determine the aggregation applied to a field because the function always appears in front of the field’s name when it is placed on a shelf. For example, Sales becomes SUM(Sales).  You can aggregate measures using Tableau only for relational data sources. Multidimensional data sources contain aggregated data only. In Tableau, multidimensional data sources are supported only in Windows.

According to Tableau, Disaggregating your data allows you to view every row of the data source which can be useful when you are analyzing measures that you may want to use both independently and dependently in the view. For example, you may be analyzing the results from a product satisfaction survey with the Age of participants along one axis. You can aggregate the Age field to determine the average age of participants or disaggregate the data to determine what age participants were most satisfied with the product.

21. What is the difference between joining and blending in Tableau?

• Joining term is used when you are combining data from the same source, for example, worksheet in an Excel file or tables in Oracle database
• While blending requires two completely defined data sources in your report.

22. What are Extracts and Schedules in Tableau server?

Data extracts are the first copies or subdivisions of the actual data from original data sources. The workbooks using data extracts instead of those using live DB connections are faster since the extracted data is imported in Tableau Engine.After this extraction of data, users can publish the workbook, which also publishes the extracts in Tableau Server. However, the workbook and extracts won’t refresh unless users apply a scheduled refresh on the extract. Scheduled Refreshes are the scheduling tasks set for data extract refresh so that they get refreshed automatically while publishing a workbook with data extract. This also removes the burden of republishing the workbook every time the concerned data gets updated.

23. How to view underlying SQL Queries in Tableau?

Viewing underlying SQL Queries in Tableau provides two options:

• Create a Performance Recording to record performance information about the main events you interact with workbook. Users can view the performance metrics in a workbook created by Tableau.
  Help -> Settings and Performance -> Start Performance Recording
  Help -> Setting and Performance -> Stop Performance Recording.
• Reviewing the Tableau Desktop Logs located at C:UsersMy DocumentsMy Tableau Repository. For live connection to data source, you can check log.txt and tabprotosrv.txt files. For an extract, check tdeserver.txt file.

24. How to do Performance Testing in Tableau?

Performance testing is again an important part of implementing tableau. This can be done by loading Testing Tableau Server with TabJolt, which is a “Point and Run” load generator created to perform QA. While TabJolt is not supported by tableau directly, it has to be installed using other open source products.

25. Name the components of a Dashboard.

• Horizontal – Horizontal layout containers allow the designer to group worksheets and dashboard components left to right across your page and edit the height of all elements at once.
• Vertical – Vertical containers allow the user to group worksheets and dashboard components top to bottom down your page and edit the width of all elements at once.
• Text – All textual fields.
• Image Extract  – A Tableau workbook is in XML format. In order to extracts images, Tableau applies some codes to extract an image which can be stored in XML.
• Web [URL ACTION] – A URL action is a hyperlink that points to a Web page, file, or other web-based resource outside of Tableau. You can use URL actions to link to more information about your data that may be hosted outside of your data source. To make the link relevant to your data, you can substitute field values of a selection into the URL as parameters.

26. How to remove ‘All’ options from a Tableau auto-filter?

27. How to add Custom Color to Tableau?

28. What is TDE file?

• Firstly, TDE is a columnar store.
• The second is how they are structured which impacts how they are loaded into memory and used by Tableau. This is an important aspect of how TDEs are “architecture aware”. Architecture-awareness means that TDEs use all parts of your computer memory, from RAM to hard disk, and put each part to work what best fits its characteristics.

29. Mention whether you can create relational joins in Tableau without creating a new table?

30. How to automate reports?

31. What is Assume referential integrity?

<!DOCTYPE html>

<html lang="en">

<head>

<title>Tableau JavaScript API </title>

<script type="text/javascript" src="http://servername/javascripts/api/tableau_v8.js"></script>

</head>

<div id="tableau Viz"></div>

<script type='text/javascript'>

var placeholderDiv = document.getElementById("tableau Viz");

var url = "http://servername/t/311/views/Mayorscreenv5/Mayorscreenv2";

var options={

hideTabs:True,

width:"100%",

height:"1000px"

};

var viz= new tableauSoftware.Viz(placeholderDiv,url,options);

setInterval (function() {viz.refreshDataAsync()},5000);

</script>

</body>

</html>

Some Additional Tricky Tableau Interview Questions

In this Angular Interview Questions article, I am going to list some of the most important Angular Interview Questions and Answers which will set you apart in the interview process in 2019. Angular continues to dominate the arena of the Javascript framework and has proved itself to be a worthy investment for web developers who seek to fast-track their career. No surprises there, Angular is majorly known for its ability to create single-page web applications that encompass three critical components – speed, agility and a strong community backing it up. Angular is known as the Swiss army knife of frontend developers! This is the reason why Angular Certification is the most in-demand certification in scripting domain.

We have compiled a list of top Angular interview questions which are classified into 3 sections, namely:

• Angular Interview Questions  – Beginners Level
• Angular Interview Questions  – Intermediate Level
• Angular Interview Questions  – Advanced Level

As an Angular professional, it is essential to know the right buzzwords, learn the right technologies and prepare the right answers to commonly asked Angular Interview Questions. Here’s a definitive list of top Angular Interview Questions that will guarantee a breeze-through to the next level.

In case you attended any Angular interview recently, or have additional questions beyond what we covered, we encourage you to post them in our QnA Forum. Our expert team will get back to you at the earliest.  

So let’s get started with the first set of basic Angular Interview Questions.

Beginners Level – Angular Interview Questions

1. Differentiate between Angular and AngularJS.

2. What is Angular?

Angular is an open-source front-end web framework. It is one of the most popular JavaScript frameworks that is mainly maintained by Google. It provides a platform for easy development of web-based applications and empowers the front end developers in curating cross-platform applications. It integrates powerful features like declarative templates, an end to end tooling, dependency injection and various other best practices that smoothens the development path.

3. What are the advantages of using Angular?

A few of the major advantages of using Angular framework are listed below:

• It supports two-way data-binding
• It follows MVC pattern architecture
• It supports static template and Angular template
• You can add a custom directive
• It also supports RESTfull services
• Validations are supported
• Client and server communication is facilitated
• Support for dependency injection
• Has strong features like Event Handlers, Animation, etc.

4. What is Angular mainly used for?

Angular is typically used for the development of SPA which stands for Single Page Applications. Angular provides a set of ready-to-use modules that simplify the development of single page applications. Not only this, with features like built-in data streaming, type safety, and a modular CLI,  Angular is regarded as a full-fledged web framework.

5. What are Angular expressions?

Angular expressions are code snippets that are usually placed in binding such as {{ expression }} similar to JavaScript. These expressions are used to bind application data to HTML

Syntax: {{ expression }}

6. What are templates in Angular?

Templates in Angular are written with HTML that contains Angular-specific elements and attributes. These templates are combined with information coming from the model and controller which are further rendered to provide the dynamic view to the user.

7. In Angular what is string interpolation?

String interpolation in Angular is a special syntax that uses template expressions within double curly {{ }} braces for displaying the component data. It is also known as moustache syntax. The JavaScript expressions are included within the curly braces to be executed by Angular and the relative output is then embedded into the HTML code. These expressions are usually updated and registered like watches, as a part of the digest cycle.

8. What is the difference between an Annotation and a Decorator in Angular?

Annotations in angular are “only” metadata set of the class using the Reflect Metadata library. They are used to create an “annotation” array. On the other hand, decorators are the design patterns that are used for separating decoration or modification of a class without actually altering the original source code.

9. What do you understand by controllers in Angular?

Controllers are JavaScript functions which provide data and logic to HTML UI. As the name suggests, they control how data flows from the server to HTML UI.

10. What is scope in Angular?

Scope in Angular is an object that refers to the application model. It is an execution context for expressions. Scopes are arranged in a hierarchical structure which mimics the DOM structure of the application. Scopes can watch expressions and propagate events.

11. What are directives in Angular?

A core feature of Angular, directives are attributes that allow you to write new HTML syntax, specific to your application. They are essentially functions that execute when the Angular compiler finds them in the DOM.  The Angular directives are segregated into 3 parts:

1. Component Directives
2. Structural Directives
3. Attribute Directives

12. What is data binding?

In Angular, data binding is one of the most powerful and important features that allow you to define the communication between the component and DOM(Document Object Model). It basically simplifies the process of defining interactive applications without having to worry about pushing and pulling data between your view or template and component. In Angular, there are four forms of data binding:

1.  String Interpolation
2. Property Binding
3. Event Binding
4. Two-Way Data Binding

13. What is the purpose of a filter in Angular?

Filters in Angular are used for formatting the value of an expression in order to display it to the user. These filters can be added to the templates, directives, controllers or services. Not just this, you can create your own custom filters. Using them, you can easily organize data in such a way that the data is displayed only if it fulfills certain criteria. Filters are added to the expressions by using the pipe character |, followed by a filter.

14. What are the differences between Angular and jQuery?

15. What is a provider in Angular?

A provider is a configurable service in Angular. It is an instruction to the Dependency Injection system that provides information about the way to obtain a value for a dependency. It is an object that has a $get() method which is called to create a new instance of a service. A Provider can also contain additional methods and uses $provide in order to register new providers.

Intermediate Level – Angular Interview Questions

16. Does Angular support nested controllers?

Yes, Angular does support the concept of nested controllers. The nested controllers are needed to be defined in a hierarchical manner for using it in the View. 

17. How can you differentiate between Angular expressions and JavaScript expressions?

18. List at down the ways in which you can communicate between applications modules using core Angular functionality.

Below are the most general ways for communicating between application modules using core Angular functionality :

• Using events
• Using services
• By assigning models on $rootScope
• Directly between controllers [$parent, $$childHead, $$nextSibling, etc.]
• Directly between controllers [ControllerAs, or other forms of inheritance]

19. What is the difference between a service() and a factory()?

A service() in Angular is a function that is used for the business layer of the application. It operates as a constructor function and is invoked once at the runtime using the ‘new’ keyword. Whereas factory() is a function which works similar to the service() but is much more powerful and flexible. factory() are design patterns which help in creating Objects.

20. What is the difference between $scope and scope in Angular?

• $scope in Angular is used for implementing the concept of dependency injection (D.I) on the other hand scope is used for directive linking.
• $scope is the service provided by $scopeProviderwhich can be injected into controllers, directives or other services whereas Scope can be anything such as a function parameter name, etc.

21. Explain the concept of scope hierarchy?

The $scope objects in Angular are organized into a hierarchy and are majorly used by views. It contains a root scope which can further contain scopes known as child scopes. One root scope can contain more than one child scopes. Here each view has its own $scope thus the variables set by its view controller will remain hidden to the other controllers. The Scope hierarchy generally looks like:

• Root $scope
  • $scope for Controller 1
  • $scope for Controller 2
  • ..
  • $scope for Controller ‘n’

22. What is AOT?

AOT stands for Angular Ahead-of-Time compiler. It is used for pre-compiling the application components and along with their templates during the build process. Angular applications which are compiled with AOT has a smaller launching time. Also, components of these applications can execute immediately, without needing any client-side compilation. Templates in these applications are embedded as code within their components. It reduces the need for downloading the Angular compiler which saves you from a cumbersome task. AOT compiler can discard the unused directives which are further thrown out using a tree-shaking tool.

23. Explain jQLite.

jQlite is also known as jQuery lite is a subset of jQuery and contains all its features. It is packaged within Angular, by default. It helps Angular to manipulate the DOM in a way that is compatible cross-browser. jQLite basically implements only the most commonly needed functionality which results in having a small footprint.

24. Explain the process of digest cycle in Angular?

The digest cycle in Angular is a process of monitoring the watchlist for keeping a track of changes in the value of the watch variable. In each digest cycle, Angular compares the previous and the new version of the scope model values. Generally, this process is triggered implicitly but you can activate it manually as well by using $apply().

25. What are the Angular Modules?

All the Angular apps are modular and follow a modularity system known as NgModules. These are the containers which hold a cohesive block of code dedicated specifically to an application domain, a workflow, or some closely related set of capabilities. These modules generally contain components, service providers, and other code files whose scope is defined by the containing NgModule.  With modules makes the code becomes more maintainable, testable, and readable. Also, all the dependencies of your applications are generally defined in modules only.

26. On which types of the component can we create a custom directive?

27. What are the different types of filters in Angular?

Below are the various filters supported by Angular:

• currency: Format a number to a currency format.
• date: Format a date to a specified format.
• filter: Select a subset of items from an array.
• json: Format an object to a JSON string.
• limit: To Limits an array/string, into a specified number of elements/characters.
• lowercase: Format a string to lower case.
• number: Format a number to a string.
• orderBy: Orders an array by an expression.
• uppercase: Format a string to upper case.

28. What is Dependency Injection in Angular? 

Dependency Injection (DI) is a software design pattern where the objects are passed as dependencies rather than hard-coding them within the component. The concept of Dependency Injection comes in handy when you are trying to separate the logic of object creation to that of its consumption. The ‘config’ operation makes use of DI that must be configured beforehand while the module gets loaded to retrieve the elements of the application. With this feature, a user can change dependencies as per his requirements.

29. Differentiate between one-way binding and two-way data binding.

In One-Way data binding, the View or the UI part does not update automatically whenever the data model changes. You need to manually write custom code in order to update it every time the view changes.

Whereas, in Two-way data binding, the View or the UI part is updated implicitly as soon as the data model changes. It is a synchronization process, unlike One-way data binding.

30. What are the lifecycle hooks for components and directives?

An Angular component has a discrete life-cycle which contains different phases as it transits through birth till death. In order to gain better control of these phases, we can hook into them using the following:

• constructor: It is invoked when a component or directive is created by calling new on the class.
• ngOnChanges: It is invoked whenever there is a change or update in any of the input properties of the component.
• ngOnInit: It is invoked every time a given component is initialized. This hook is only once called in its lifetime after the first ngOnChanges.
• ngDoCheck: It is invoked whenever the change detector of the given component is called. This allows you to implement your own change detection algorithm for the provided component.
• ngOnDestroy: It is invoked right before the component is destroyed by Angular. You can use this hook in order to unsubscribe observables and detach event handlers for avoiding any kind of memory leaks.

31. What do you understand by dirty checking in Angular?

In Angular, the digest process is known as dirty checking. It is called so as it scans the entire scope for changes. In other words, it compares all the new scope model values with the previous scope values. Since all the watched variables are contained in a single loop, any change/update in any of the variable leads to reassigning of rest of the watched variables present inside the DOM. A watched variable is in a single loop(digest cycle), any value change of any variable forces to reassign values of other watched variables in DOM

32. Differentiate between DOM and BOM.

33. What is Transpiling in Angular?
Transpiling in Angular refers to the process of conversion of the source code from one programming language to another. In Angular, generally, this conversion is done from TypeScript to JavaScript. It is an implicit process and happens internally.

34. How to perform animation in Angular?

In order to perform animation in an Angular application, you need to include a special Angular library known as Animate Library and then refer to the ngAnimate module into your application or add the ngAnimate as a dependency inside your application module.

35. What is transclusion in Angular?

The transclusion in Angular allows you to shift the original children of a directive into a specific location within a new template. The ng directive indicates the insertion point for a transcluded DOM of the nearest parent directive that is using transclusion. Attribute directives like ng-transclude or ng-transclude-slot are mainly used for transclusion.

36. What are events in Angular?

Events in Angular are specific directives that help in customizing the behavior of various DOM events. Few of the events supported by Angular are listed below:

• ng-click
• ng-copy
• ng-cut
• ng-dblclick
• ng-keydown
• ng-keypress
• ng-keyup
• ng-mousedown
• ng-mouseenter
• ng-mouseleave
• ng-mousemove
• ng-mouseover
• ng-mouseup
• ng-blur

37. List some tools for testing angular applications?

1. Karma
2. Angular Mocks
3. Mocha
4. Browserify
5. Sion

38. How to create a service in Angular?

In Angular, a service is a substitutable object that is wired together using dependency injection. A service is created by registering it in the module it is going to be executed within. There are basically three ways in which you can create an angular service. They are basically three ways in which a service can be created in Angular:

• Factory
• Service
• Provider

39. What is a singleton pattern and where we can find it in Angular?

Singleton pattern in Angular is a great pattern which restricts a class from being used more than once. Singleton pattern in Angular is majorly implemented on dependency injection and in the services. Thus, if you use ‘new Object()’ without making it a singleton, then two different memory locations will be allocated for the same object. Whereas, if the object is declared as a singleton, in case it already exists in the memory then simply it will be reused.

40. What do you understand by REST in Angular?

REST stands for REpresentational State Transfer. REST is an API (Application Programming Interface) style that works on the HTTP request. In this, the requested URL pinpoints the data that needs to be processed. Further ahead, an HTTP method then identifies the specific operation that needs to be performed on that requested data. Thus, the APIs which follows this approach are known as RESTful APIs.

41. What is bootstrapping in Angular?

Bootstrapping in Angular is nothing but initializing, or starting the Angular app. Angular supports automatic and manual bootstrapping.

• Automatic Bootstrapping: this is done by adding the ng-app directive to the root of the application, typically on the tag or tag if you want angular to bootstrap your application automatically. When Angular finds ng-app directive, it loads the module associated with it and then compiles the DOM.
• Manual Bootstrapping: Manual bootstrapping provides you more control on how and when to initialize your Angular application. It is useful where you want to perform any other operation before Angular wakes up and compile the page.

42. What is the difference between a link and compile in Angular?

• Compile function is used for template DOM Manipulation and to collect all the directives.
• Link function is used for registering DOM listeners as well as instance DOM manipulation and is executed once the template has been cloned.

43. What do you understand by constants in Angular?

In Angular, constants are similar to the services which are used to define the global data. Constants are declared using the keyword “constant”. They are created using constant dependency and can be injected anywhere in controller or services.

44. What is the difference between a provider, a service and a factory in Angular?

45. What are Angular Global APIs?

Angular Global API is a combination of global JavaScript functions for performing various common tasks like:

• Comparing objects
• Iterating objects
• Converting data

There are some common Angular Global API functions like:

• angular. lowercase: Converts a string to lowercase string.
• angular. uppercase: Converts a string to uppercase string.
• angular. isString: Returns true if the current reference is a string.
• angular. isNumber: Returns true if the current reference is a number.

Advanced Level – Angular Interview Questions

46. In Angular, describe how will you set, get and clear cookies?

For using cookies in Angular, you need to include a  module called ngCookies angular-cookies.js.

To set Cookies – For setting the cookies in a key-value format ‘put’ method is used.

cookie.set('nameOfCookie',"cookieValue");

To get Cookies – For retrieving the cookies ‘get’ method is used.

cookie.get(‘nameOfCookie’);

To clear Cookies – For removing cookies ‘remove’ method is used.

cookie.delete(‘nameOfCookie’);

47.  If your data model is updated outside the ‘Zone’, explain the process how will you the view?

You can update your view using any of the following:

1. ApplicationRef.prototype.tick(): It will perform change detection on the complete component tree.
2. NgZone.prototype.run(): It will perform the change detection on the entire component tree. Here, the run() under the hood will call the tick itself and then parameter will take the function before tick and executes it.
3. ChangeDetectorRef.prototype.detectChanges(): It will launch the change detection on the current component and its children.

48. Explain ng-app directive in Angular.

ng-app directive is used to define Angular applications which let us use the auto-bootstrap in an Angular application. It represents the root element of an Angular application and is generally declared near <html> or <body> tag. Any number of ng-app directives can be defined within an HTML document but just a single Angular application can be officially bootstrapped implicitly. Rest of the applications must be manually bootstrapped. 

Example

49. What is the process of inserting an embedded view from a prepared TemplateRef?

@Component({
    selector: 'app-root',
    template: `
        <ng-template #template let-name='fromContext'><div>{{name}}</ng-template>
    `
})
export class AppComponent implements AfterViewChecked {
    @ViewChild('template', { read: TemplateRef }) _template: TemplateRef<any>;
    constructor() { }

    ngAfterViewChecked() {
        this.vc.createEmbeddedView(this._template, {fromContext: 'John'});
    }
}

50. How can you hide an HTML element just by a button click in angular?

An HTML element can be easily hidden using the ng-hide directive in conjunction along with a controller to hide an HTML element on button click.

View

<div ng-controller="MyController">
  <button ng-click="hide()">Hide element</button>
  <p ng-hide="isHide">Hello World!</p>
</div>

Controller

controller: function() {
this.isHide = false;
this.hide = function(){
this.isHide = true; }; }

So this brings us to the end of the Angular interview questions article. The topics that you learned in this Angular Interview Questions article are the most sought-after skill sets that recruiters look for in an Angular Professional. These set of Angular Interview Questions will definitely help you ace your job interview. Good luck with your interview!

If you found this “Angular Interview Questions” relevant, check out the Angular Certification Training by Edureka, a trusted online learning company with a network of more than 250,000 satisfied learners spread across the globe. 

Got a question for us? Please mention it in the comments section of this Angular Interview Questions and we will get back to you.

Over the last one year or so, I’ve met a lot of people who have varying degrees of ambiguity around AWS certifications and which certification to choose for their specific nature of work or towards their career goals. This blog aims to demystify these ambiguities and provide clarity on what each AWS certification entails. For starters, let’s understand what AWS is and what certifications it provides:

Amazon Web Services (AWS), the popular cloud platform, houses a collection of cloud computing services, that have opened up hot career prospects in the world of cloud computing.  AWS has more than 70 services, spanning a wide range, including compute, storage, networking, database, analytics, application services, deployment, management, mobile, developer tools and Internet of things. AWS also offers cloud certifications that assert your ability to operate on the cloud. There are five different certifications and each of them open the floodgates to enhanced career opportunities. Depending on your interest and career goals, you can choose to engage yourself in any of the two certification tracks prescribed by AWS. Let me now break them down for you, one by one.

AWS suite of certifications

AWS certifications are aligned to two broad streams – Solutions Architect and DevOps Engineer. The Solutions Architect stream is well defined; you should first bag the Solutions Architect – Associate certification followed by the Solutions Architect – Professional certification. But if you choose to certify yourself as an AWS DevOps Engineer, you have to either clear the Developer – Associate certification or the System Operations (SysOps) Administrator – Associate certifications. Of course, you should choose based on your current job or the stream of specialization you aspire for.

Alternatively, AWS allows you to containerize its suite of certifications into three blocks – Solutions Architect, Developer and SysOps. While Solutions Architect is an independent stream in itself, a Developer and/or SysOps Associate certification can lead you to a DevOps Engineer certification.

I have good news for you. The associate certifications of Solutions Architect and Developer share 50% content between them. So if you prepare for one, you’ve pretty much prepared half of the other as well. While most people I’ve met feel that Developer is the easiest to crack, Solutions Architect makes you a master of almost all of AWS’ services and helps you understand all key concepts. SysOps, on the other hand, is an ideal starting point if you are currently working as an infrastructure/system admin and/or are managing VMs, storage or networking in your current job.

AWS Certification Job Prospects

According to Forbes, AWS Certified Solution Architect – Associate is the number 1 certification program of 2016. In its global survey of top 15 certifications in 2016, Solutions Architect, with a median salary of $125,871, is the highest paying certification. Additionally, all of AWS’ certifications will help you earn salaries in excess of $100,000. Specific Solution Architect skills that recruiters look for include designing on AWS, selecting the appropriate AWS services for your business, ingress and egress of data to and from the AWS, estimating AWS costs and identifying cost-control measures for your organization.

Globally, there are more than 380,000 cloud computing jobs in the IT industry itself. With cloud computing pervading into almost every business vertical, the need for qualified and certified cloud professionals is ever-growing. AWS is currently leading the pack with most companies having invested in or planning to invest in AWS tools and services. This is a clear sign that good times are in store for you if you commit yourself to AWS.

Which AWS Certification should you choose?

Depending on your interest, career goal and experience, you can decide which certification to go for. It is important to note that the Associate-level certifications do not require to have any prior AWS experience. However, experts believe around 1 year of experience with any of the AWS tools will be a great help in cracking the exams faster. The three Professional exams mandate 2 or more years of hands-on experience on AWS, but Amazon takes your word for it and does not require you to furnish any proof of experience. Let me now explain what you will achieve with each of these certifications:

Do you wish to get certified as an AWS Solutions Architect already? Our live, instructor-led course will help you prepare for the exam by mastering concepts around EC2, EIP, ELB, EBS, S3, and lots more. Check out full details here. 

The Edureka course AWS Development Certification Training is specially curated to help you crack the AWS exam and become a certified developer. This live, instructor-led course helps you master concepts like cloud essentials, models, services and mastering AWS services and much more. Click here to know more. 

Edureka tips and recommendations for AWS Certification

Now, here’s that part of the blog where I provide you a cheat sheet to ace your AWS certification. While each AWS certification has a different level of complexity, there are certain common tips that can help you become battle-ready.

• Do remember that you need to pay a fees of $150 to enroll for the Associate exams and $300 to enroll for the Professional exams.
• Questions are usually in multiple choice format with the pass percentage changing with every exam, based on statistical analysis by Amazon.
• An average Associate-level exam lasts for about 80 minutes with around 60 minutes, with a pass percentage of 60%.
• For effective practice prior to taking the exam, we recommend you sign up with Amazon and activate the AWS Free Tier, which includes 750 hours of both Linux and Windows instances with 30 GB of EBS storage each month for one year for new AWS customers.
• Utilize this space and time to get hands-on experience on AWS tools and operations. This is the most important aspect of the certifications, and the easiest ways to understand core concepts.
• Additionally, you can check out the Exam Blueprint mentioned in the AWS website for detailed information on specific exam modules.

I hope I’ve been able to help you de-clutter your head about AWS certifications. If you have attempted any of these exams in the recent past, I need to hear from you! Place your comments below and let’s connect.

If you have decided to prepare for an AWS certification, you should check out our courses on AWS Architect and AWS Development. Each of these courses is specially curated by industry experts, and come with live, real-life project experience and 24/7 technical support.

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Deep dive into Amazon S3

The Great White is considered to be the King of the Ocean. This is because the great White is on top of its game. Imagine if you could be on top of the game in the ocean of Big Data!

Big Data is everywhere and there is almost an urgent need to collect and preserve whatever data is being generated, for the fear of missing out on something important. There is a huge amount of data floating around. What we do with it is all that matters right now. This is why Big Data Analytics is in the frontiers of IT. Big Data Analytics has become crucial as it aids in improving business, decision makings and providing the biggest edge over the competitors. This applies for organizations as well as professionals in the Analytics domain. For professionals, who are skilled in Big Data Analytics, there is an ocean of opportunities out there.

Why Big Data Analytics is the Best Career move

If you are still not convinced by the fact that Big Data Analytics is one of the hottest skills, here are 10 more reasons for you to see the big picture.

1. Soaring Demand for Analytics Professionals:

Jeanne Harris, senior executive at Accenture Institute for High Performance, has stressed the significance of analytics professionals by saying, “…data is useless without the skill to analyze it.” There are more job opportunities in Big Data management and Analytics than there were last year and many IT professionals are prepared to invest time and money for the training.

The job trend graph for Big Data Analytics, from Indeed.com, proves that there is a growing trend for it and as a result there is a steady increase in the number of job opportunities.

Source: Indeed.com

The current demand for qualified data professionals is just the beginning. Srikanth Velamakanni, the Bangalore-based cofounder and CEO of CA headquartered Fractal Analytics states: “In the next few years, the size of the analytics market will evolve to at least one-thirds of the global IT market from the current one-tenths”.

Technology professionals who are experienced in Analytics are in high demand as organizations are looking for ways to exploit the power of Big Data. The number of job postings related to Analytics in Indeed and Dice has increased substantially over the last 12 months. Other job sites are showing similar patterns as well. This apparent surge is due to the increased number of organizations implementing Analytics and thereby looking for Analytics professionals.

In a study by QuinStreet Inc., it was found that the trend of implementing Big Data Analytics is zooming and is considered to be a high priority among U.S. businesses. A majority of the organizations are in the process of implementing it or actively planning to add this feature within the next two years.

You can watch the sample class recording of Edureka’s Big Data and Hadoop course here:

2. Huge Job Opportunities & Meeting the Skill Gap:

The demand for Analytics skill is going up steadily but there is a huge deficit on the supply side. This is happening globally and is not restricted to any part of geography. In spite of Big Data Analytics being a ‘Hot’ job, there is still a large number of unfilled jobs across the globe due to shortage of required skill. A McKinsey Global Institute study states that the US will face a shortage of about 190,000 data scientists and 1.5 million managers and analysts who can understand and make decisions using Big Data by 2018.

To get in-depth knowledge on Data Science, you can enroll for live Data Science Certification Training by Edureka with 24/7 support and lifetime access.

India, currently has the highest concentration of analytics globally. In spite of this, the scarcity of data analytics talent is particularly acute and demand for talent is expected to be on the higher side  as more global organizations are outsourcing their work.

According to Srikanth Velamakanni, co-founder and CEO of Fractal Analytics, there are two types of talent deficits: Data Scientists, who can perform analytics and Analytics Consultant, who can understand and use data. The talent supply for these job title, especially Data Scientists is extremely scarce and the demand is huge.

3. Salary Aspects:

Strong demand for Data Analytics skills is boosting the wages for qualified professionals and making Big Data pay big bucks for the right skill. This phenomenon is being seen globally where countries like Australia and the U.K are witnessing this ‘Moolah Marathon’.

According to the 2015 Skills and Salary Survey Report published by the Institute of Analytics Professionals of Australia (IAPA), the annual median salary for data analysts is $130,000, up four per cent from last year. Continuing the trend set in 2013 and 2014, the median respondent earns 184% of the Australian full-time median salary. The rising demand for analytics professionals is also reflected in IAPA’s membership, which has grown to more than 5000 members in Australia since its formation in 2006.

Randstad states that the annual pay hikes for Analytics professionals in India is on an average 50% more than other IT professionals. According to The Indian Analytics Industry Salary Trend Report by Great Lakes Institute of Management, the average salaries for analytics professionals in India was up by 21% in 2015 as compared to 2014. The report also states that 14% of all analytics professionals get a salary of more than Rs. 15 lakh per annum.

A look at the salary trend for Big Data Analytics in the UK also indicates a positive and exponential growth. A quick search on Itjobswatch.co.uk shows a median salary of £62,500 in early 2016 for Big Data Analytics jobs, as compared to £55,000 in the same period in 2015. Also, a year-on-year median salary change of +13.63% is observed.

The table below looks at the statistics for Big Data Analytics skills in IT jobs advertised across the UK. Included is a guide to the salaries offered in IT jobs that have cited Big Data Analytics over the 3 months to 23 June 2016 with a comparison to the same period over the previous 2 years.

4. Big Data Analytics: A Top Priority in a lot of Organizations

According to the ‘Peer Research – Big Data Analytics’ survey, it was concluded that Big Data Analytics is one of the top priorities of the organizations participating in the survey as they believe that  it improves the performances of their organizations.

Based on the responses, it was found that approximately 45% of the surveyed believe that Big Data analytics will enable much more precise business insights, 38% are looking to use Analytics to recognize sales and market opportunities. More than 60% of the respondents are depending on Big Data Analytics to  boost the organization’s social media marketing abilities. The QuinStreet research based on their survey also back the fact that Analytics is the need of the hour, where 77% of the respondents consider Big Data Analytics a top priority.

A survey by Deloitte, Technology in the Mid-Market; Perspectives and Priorities, reports that executives clearly see the value of analytics. Based on the survey, 65.2% of respondents are using some form of analytics that is helping their business needs. The image below clearly depicts their attitude and belief towards Big Data Analytics.

5. Adoption of Big Data Analytics is Growing:

New technologies are now making it easier to perform increasingly sophisticated data analytics on a very large and diverse datasets. This is evident as the report from The Data Warehousing Institute (TDWI) shows. According to this report, more than a third of the respondents are currently using some form of advanced analytics on Big Data,  for Business Intelligence, Predictive Analytics and Data Mining tasks.

With Big Data Analytics providing an edge over the competition, the rate of implementation of the necessary Analytics tools has increased exponentially. In fact, most of the respondents of the  ‘Peer Research – Big Data Analytics’ survey reported that they already have a strategy setup for dealing with Big Data Analytics. And those who are yet to come up with a strategy are also in the process of planning for it.

When it comes to Big Data Analytics tools, the adoption of Apache Hadoop framework continues to be the popular choice. There are various commercial and open-source frameworks to choose from and organizations are making the appropriate choice based on their requirement. Over half of the respondents have already deployed or are currently implementing a Hadoop distribution. Out of them, a quarter of the respondents have deployed open-source framework, which is twice the number of organizations that have deployed a commercial distribution of the Hadoop framework.

6. Analytics: A Key Factor in Decision Making

Analytics is a key competitive resource for many companies. There is no doubt about that. According to the ‘Analytics Advantage’ survey overseen by Tom Davenport, ninety six percent of respondents feel that analytics will become more important to their organizations in the next three years. This is because there is a huge amount of data that is not being used and at this point, only rudimentary analytics is being done. About forty nine percent of the respondents strongly believe that analytics is a key factor in better decision-making capabilities. Another sixteen percent like it for its superior key strategic initiatives.

Even though there is a fight for the title of ‘Greatest Benefit of Big Data Analytics’, one thing is undeniable and stands out the most: Analytics play an important role in driving business strategy and making effective business decisions.

Seventy Four percent of the respondents of the ‘Peer-Research Big Data Analytics Survey’ have agreed that Big Data Analytics is adding value to their organization and allows vital information for making timely and effective business decisions of great importance. This is a clear indicator than Big Data Analytics is here to stay and a career in it is the wisest decision one can make.

7. The Rise of Unstructured and Semistructured Data Analytics:

The ‘Peer Research – Big Data Analytics’ survey clearly reports that there is a huge growth when it comes to unstructured and semistructured data analytics. Eighty four percent of the respondents have mentioned that the organization they work for are currently processing and analyzing unstructured data sources, including weblogs, social media, e-mail, photos, and video. The remaining respondents have indicated that steps are being taken to implement them in the next 12 to 18 months.

8. Big Data Analytics is Used Everywhere!

It is a given that there is a huge demand for Big Data Analytics owing to its awesome features. The tremendous growth is also due to the varied domain across which Analytics is being utilized. The image below depicts the job opportunities across various domains.

9. Surpassing Market Forecast / Predictions for Big Data Analytics:

Big Data Analytics has  topped a survey carried out by Nimbus Ninety, as the most disruptive technologies that will have the biggest influence in three years’ time. Added to this, there are more market forecasts that support this:

• According to IDC, the Big Data Analytics market will reach $125 billion worldwide in 2015.
• IIA states that Big Data Analytics tools will be the first line of defense, combining machine learning, text mining and ontology modeling to provide holistic and integrated security threat prediction, detection, and deterrence and prevention programs.
• According to the survey ‘The Future of Big Data Analytics – Global Market and Technologies Forecast – 2015-2020’, Big Data Analytics Global Market will grow by 14.4% CAGR over this period.

• The Big Data Analytics Global Market for Apps and Analytics Technology will grow by 28.2% CAGR, for  Cloud Technology will grow by 16.1% CAGR, for Computing Technology will grow by 7.1% CAGR, for NoSQL Technology will grow by 18.9% CAGR  over the entire 2015-2020 period.

10. Numerous Choices in Job Titles and Type of Analytics :

From a career point of view, there are so many option available, in terms of domain as well as nature of job. Since Analytics is utilized in varied fields, there are numerous job titles for one to choose from.

• Big Data Analytics Business Consultant
• Big Data Analytics Architect
• Big Data Engineer
• Big Data Solution Architect
• Big Data Analyst
• Analytics Associate
• Business Intelligence and Analytics Consultant
• Metrics and Analytics Specialist

Big Data Analytics career is deep and one can choose from the 3 types of data analytics depending on the Big Data environment.

• Prescriptive Analytics
• Predictive Analytics
• Descriptive Analytics.

A huge array of organizations like Ayata, IBM, Alteryx, Teradata, TIBCO, Microsoft, Platfora, ITrend, Karmasphere, Oracle, Opera, Datameer, Pentaho, Centrofuge, FICO, Domo, Quid, Saffron, Jaspersoft, GoodData, Bluefin Labs, Tracx, Panaroma Software, and countless more are utilizing Big Data Analytics for their business needs and a huge job opportunities are possible with them.

Conclusion:

Analytics no matter how advanced they are, does not remove the need for human insights. On the contrary, there is a compelling need for skilled people with the ability to understand data, think from the business point of view and come up with insights. For this very reason technology professionals with Analytics skill are finding themselves in high demand as businesses look to harness the power of Big Data. A professional with the Analytical skills can master the ocean of Big Data and become a vital asset to an organization, boosting the business and their career.

Got a question for us? Please mention them in the comments section and we will get back to you.

Related Posts:

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Hadoop Tutorial for Beginners

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Python Certification is the most sought-after skill in programming domain. In this Python Interview Questions blog, I will introduce you to the most frequently asked questions in Python interviews. Our Python Interview Questions is the one-stop resource from where you can boost your interview preparation. We have 100+ questions on Python Programming basics which will help you with different expertise levels to reap the maximum benefit from our blog.

If you have other doubts regarding Python, feel free to post them in our QnA Forum. Our expert team will get back to you at the earliest.

Basic Python Interview Questions

Q1. What is the difference between list and tuples in Python?

Q2. What are the key features of Python?

• Python is an interpreted language. That means that, unlike languages like C and its variants, Python does not need to be compiled before it is run. Other interpreted languages include PHP and Ruby.
• Python is dynamically typed, this means that you don’t need to state the types of variables when you declare them or anything like that. You can do things like x=111 and then x="I'm a string" without error
• Python is well suited to object orientated programming in that it allows the definition of classes along with composition and inheritance. Python does not have access specifiers (like C++’s public, private).
• In Python, functions are first-class objects. This means that they can be assigned to variables, returned from other functions and passed into functions. Classes are also first class objects
• Writing Python code is quick but running it is often slower than compiled languages. Fortunately，Python allows the inclusion of C based extensions so bottlenecks can be optimized away and often are. The numpy package is a good example of this, it’s really quite quick because a lot of the number crunching it does isn’t actually done by Python
• Python finds use in many spheres – web applications, automation, scientific modeling, big data applications and many more. It’s also often used as “glue” code to get other languages and components to play nice.

Q3. What type of language is python? Programming or scripting?

Ans: Python is capable of scripting, but in general sense, it is considered as a general-purpose programming language. To know more about Scripting, you can refer to the Python Scripting Tutorial.

Q4.How is Python an interpreted language?

Ans: An interpreted language is any programming language which is not in machine level code before runtime. Therefore, Python is an interpreted language.

Q5.What is pep 8?

Ans: PEP stands for Python Enhancement Proposal. It is a set of rules that specify how to format Python code for maximum readability.

Q6. How is memory managed in Python?

Ans: 

1. Memory management in python is managed by Python private heap space. All Python objects and data structures are located in a private heap. The programmer does not have access to this private heap. The python interpreter takes care of this instead.
2. The allocation of heap space for Python objects is done by Python’s memory manager. The core API gives access to some tools for the programmer to code.
3. Python also has an inbuilt garbage collector, which recycles all the unused memory and so that it can be made available to the heap space.

Q7. What is namespace in Python?

Ans: A namespace is a naming system used to make sure that names are unique to avoid naming conflicts.

Q8. What is PYTHONPATH?

Ans: It is an environment variable which is used when a module is imported. Whenever a module is imported, PYTHONPATH is also looked up to check for the presence of the imported modules in various directories. The interpreter uses it to determine which module to load.

Q9. What are python modules? Name some commonly used built-in modules in Python?

Ans: Python modules are files containing Python code. This code can either be functions classes or variables. A Python module is a .py file containing executable code.

Some of the commonly used built-in modules are:

• os
• sys
• math
• random
• data time
• JSON

Q10.What are local variables and global variables in Python?

Global Variables:

Variables declared outside a function or in global space are called global variables. These variables can be accessed by any function in the program.

Local Variables:

Any variable declared inside a function is known as a local variable. This variable is present in the local space and not in the global space.

Example:

a=2                       #Global Variable
def add(): 
b=3                       #Local Variable
c=a+b 
print(c) 
add()

Output: 5

When you try to access the local variable outside the function add(), it will throw an error.

Q11. Is python case sensitive?

Ans: Yes. Python is a case sensitive language.

Q12.What is type conversion in Python?

Ans: Type conversion refers to the conversion of one data type iinto another.

int() – converts any data type into integer type

float() – converts any data type into float type

ord() – converts characters into integer

hex() – converts integers to hexadecimal

oct() – converts integer to octal

tuple() – This function is used to convert to a tuple.

set() – This function returns the type after converting to set.

list() – This function is used to convert any data type to a list type.

dict() – This function is used to convert a tuple of order (key,value) into a dictionary.

str() – Used to convert integer into a string.

complex(real,imag) – This functionconverts real numbers to complex(real,imag) number.

Q13. How to install Python on Windows and set path variable?

Ans: To install Python on Windows, follow the below steps:

• Install python from this link: https://www.python.org/downloads/
• After this, install it on your PC. Look for the location where PYTHON has been installed on your PC using the following command on your command prompt: cmd python. 
• Then go to advanced system settings and add a new variable and name it as PYTHON_NAME and paste the copied path.
• Look for the path variable, select its value and select ‘edit’.
• Add a semicolon towards the end of the value if it’s not present and then type %PYTHON_HOME% 

Q14. Is indentation required in python?

Ans: Indentation is necessary for Python. It specifies a block of code. All code within loops, classes, functions, etc is specified within an indented block. It is usually done using four space characters. If your code is not indented necessarily, it will not execute accurately and will throw errors as well.

Q15. What is the difference between Python Arrays and lists?

Ans: Arrays and lists, in Python, have the same way of storing data. But, arrays can hold only a single data type elements whereas lists can hold any data type elements.

Example:

import array as arr
My_Array=arr.array('i',[1,2,3,4])
My_list=[1,'abc',1.20]
print(My_Array)
print(My_list)

Output:

array(‘i’, [1, 2, 3, 4]) [1, ‘abc’, 1.2]

Q16. What are functions in Python?

Ans: A function is a block of code which is executed only when it is called. To define a Python function, the def keyword is used.

Example:

def Newfunc():
print("Hi, Welcome to Edureka")
Newfunc(); #calling the function

Output: Hi, Welcome to Edureka

Q17.What is __init__?

Ans: __init__ is a method or constructor in Python. This method is automatically called to allocate memory when a new object/ instance of a class is created. All classes have the __init__ method.

Here is an example of how to use it.

class Employee:
def __init__(self, name, age,salary):
self.name = name
self.age = age
self.salary = 20000
E1 = Employee("XYZ", 23, 20000)
# E1 is the instance of class Employee.
#__init__ allocates memory for E1. 
print(E1.name)
print(E1.age)
print(E1.salary)

Output:

XYZ

23

20000

Q18.What is a lambda function?

Ans: An anonymous function is known as a lambda function. This function can have any number of parameters but, can have just one statement.

Example:

a = lambda x,y : x+y
print(a(5, 6))

Output: 11

Q19. What is self in Python?

Ans: Self is an instance or an object of a class. In Python, this is explicitly included as the first parameter. However, this is not the case in Java where it’s optional.  It helps to differentiate between the methods and attributes of a class with local variables.

The self variable in the init method refers to the newly created object while in other methods, it refers to the object whose method was called.

Q20. How does break, continue and pass work?

Q21. What does [::-1} do?

import array as arr
My_Array=arr.array('i',[1,2,3,4,5])
My_Array[::-1]

Output: array(‘i’, [5, 4, 3, 2, 1])

Q22. How can you randomize the items of a list in place in Python?

Ans: Consider the example shown below:

from random import shuffle
x = ['Keep', 'The', 'Blue', 'Flag', 'Flying', 'High']
shuffle(x)
print(x)

The output of the following code is as below.

['Flying', 'Keep', 'Blue', 'High', 'The', 'Flag']

Q23. What are python iterators?

Ans: Iterators are objects which can be traversed though or iterated upon.

Q24. How can you generate random numbers in Python?

Ans: Random module is the standard module that is used to generate a random number. The method is defined as:

import random
random.random

The statement random.random() method return the floating point number that is in the range of [0, 1). The function generates random float numbers. The methods that are used with the random class are the bound methods of the hidden instances. The instances of the Random can be done to show the multi-threading programs that creates a different instance of individual threads. The other random generators that are used in this are:

1. randrange(a, b): it chooses an integer and define the range in-between [a, b). It returns the elements by selecting it randomly from the range that is specified. It doesn’t build a range object.
2. uniform(a, b): it chooses a floating point number that is defined in the range of [a,b).Iyt returns the floating point number
3. normalvariate(mean, sdev): it is used for the normal distribution where the mu is a mean and the sdev is a sigma that is used for standard deviation.
4. The Random class that is used and instantiated creates an independent multiple random number generators.

Q25. What is the difference between range & xrange?

Ans: For the most part, xrange and range are the exact same in terms of functionality. They both provide a way to generate a list of integers for you to use, however you please. The only difference is that range returns a Python list object and x range returns an xrange object.

This means that xrange doesn’t actually generate a static list at run-time like range does. It creates the values as you need them with a special technique called yielding. This technique is used with a type of object known as generators. That means that if you have a really gigantic range you’d like to generate a list for, say one billion, xrange is the function to use.

This is especially true if you have a really memory sensitive system such as a cell phone that you are working with, as range will use as much memory as it can to create your array of integers, which can result in a Memory Error and crash your program. It’s a memory hungry beast.

Q26. How do you write comments in python?

Ans: Comments in Python start with a # character. However, alternatively at times, commenting is done using docstrings(strings enclosed within triple quotes).

Example:

#Comments in Python start like this
print("Comments in Python start with a #")

Output:  Comments in Python start with a #

Q27. What is pickling and unpickling?

Ans: Pickle module accepts any Python object and converts it into a string representation and dumps it into a file by using dump function, this process is called pickling. While the process of retrieving original Python objects from the stored string representation is called unpickling.

Q28. What are the generators in python?

Ans: Functions that return an iterable set of items are called generators.

Q29. How will you capitalize the first letter of string?

Ans: In Python, the capitalize() method capitalizes the first letter of a string. If the string already consists of a capital letter at the beginning, then, it returns the original string.

Q30. How will you convert a string to all lowercase?

Ans: To convert a string to lowercase, lower() function can be used.

Example:

stg='ABCD'
print(stg.lower())

Output: abcd

Q31. How to comment multiple lines in python?

Ans: Multi-line comments appear in more than one line. All the lines to be commented are to be prefixed by a #. You can also a very good shortcut method to comment multiple lines. All you need to do is hold the ctrl key and left click in every place wherever you want to include a # character and type a # just once. This will comment all the lines where you introduced your cursor.

Q32.What are docstrings in Python?

Ans: Docstrings are not actually comments, but, they are documentation strings. These docstrings are within triple quotes. They are not assigned to any variable and therefore, at times, serve the purpose of comments as well.

Example:

"""
Using docstring as a comment.
This code divides 2 numbers
"""
x=8
y=4
z=x/y
print(z)

Output: 2.0

Q33. What is the purpose of is, not and in operators?

Ans: Operators are special functions. They take one or more values and produce a corresponding result.

is: returns true when 2 operands are true  (Example: “a” is ‘a’)

not: returns the inverse of the boolean value

in: checks if some element is present in some sequence

Q34. What is the usage of help() and dir() function in Python?

Ans: Help() and dir() both functions are accessible from the Python interpreter and used for viewing a consolidated dump of built-in functions. 

1. Help() function: The help() function is used to display the documentation string and also facilitates you to see the help related to modules, keywords, attributes, etc.
2. Dir() function: The dir() function is used to display the defined symbols.

Q35. Whenever Python exits, why isn’t all the memory de-allocated?

Ans: 

1. Whenever Python exits, especially those Python modules which are having circular references to other objects or the objects that are referenced from the global namespaces are not always de-allocated or freed.
2. It is impossible to de-allocate those portions of memory that are reserved by the C library.
3. On exit, because of having its own efficient clean up mechanism, Python would try to de-allocate/destroy every other object.

Q36. What is a dictionary in Python?

Ans: The built-in datatypes in Python is called dictionary. It defines one-to-one relationship between keys and values. Dictionaries contain pair of keys and their corresponding values. Dictionaries are indexed by keys.

Let’s take an example:

The following example contains some keys. Country, Capital & PM. Their corresponding values are India, Delhi and Modi respectively.

dict={'Country':'India','Capital':'Delhi','PM':'Modi'}

print dict[Country]

India

print dict[Capital]

Delhi

print dict[PM]

Modi

Q37. How can the ternary operators be used in python?

Ans: The Ternary operator is the operator that is used to show the conditional statements. This consists of the true or false values with a statement that has to be evaluated for it.

Syntax:

The Ternary operator will be given as:
[on_true] if [expression] else [on_false]x, y = 25, 50big = x if x < y else y

Example:

The expression gets evaluated like if x<y else y, in this case if x<y is true then the value is returned as big=x and if it is incorrect then big=y will be sent as a result.

Q38. What does this mean: *args, **kwargs? And why would we use it?

Ans: We use *args when we aren’t sure how many arguments are going to be passed to a function, or if we want to pass a stored list or tuple of arguments to a function. **kwargs is used when we don’t know how many keyword arguments will be passed to a function, or it can be used to pass the values of a dictionary as keyword arguments. The identifiers args and kwargs are a convention, you could also use *bob and **billy but that would not be wise.

Q39. What does len() do?

Ans: It is used to determine the length of a string, a list, an array, etc.

Example:

stg='ABCD'
len(stg)

Q40. Explain split(), sub(), subn() methods of “re” module in Python.

Ans: To modify the strings, Python’s “re” module is providing 3 methods. They are:

• split() – uses a regex pattern to “split” a given string into a list.
• sub() – finds all substrings where the regex pattern matches and then replace them with a different string
• subn() – it is similar to sub() and also returns the new string along with the no. of replacements.

Q41. What are negative indexes and why are they used?

Ans: The sequences in Python are indexed and it consists of the positive as well as negative numbers. The numbers that are positive uses ‘0’ that is uses as first index and ‘1’ as the second index and the process goes on like that.

The index for the negative number starts from ‘-1’ that represents the last index in the sequence and ‘-2’ as the penultimate index and the sequence carries forward like the positive number.

The negative index is used to remove any new-line spaces from the string and allow the string to except the last character that is given as S[:-1]. The negative index is also used to show the index to represent the string in correct order.

Q42. What are Python packages?

Ans: Python packages are namespaces containing multiple modules.

Q43.How can files be deleted in Python?

Ans: To delete a file in Python, you need to import the OS Module. After that, you need to use the os.remove() function.

Example:

import os
os.remove("xyz.txt")

Q44. What are the built-in types of python?

Ans: Built-in types in Python are as follows –

• Integers
• Floating-point
• Complex numbers
• Strings
• Boolean
• Built-in functions

Q45. What advantages do NumPy arrays offer over (nested) Python lists?

Ans: 

1. Python’s lists are efficient general-purpose containers. They support (fairly) efficient insertion, deletion, appending, and concatenation, and Python’s list comprehensions make them easy to construct and manipulate.
2. They have certain limitations: they don’t support “vectorized” operations like elementwise addition and multiplication, and the fact that they can contain objects of differing types mean that Python must store type information for every element, and must execute type dispatching code when operating on each element.
3. NumPy is not just more efficient; it is also more convenient. You get a lot of vector and matrix operations for free, which sometimes allow one to avoid unnecessary work. And they are also efficiently implemented.
4. NumPy array is faster and You get a lot built in with NumPy, FFTs, convolutions, fast searching, basic statistics, linear algebra, histograms, etc. 

Q46. How to add values to a python array?

Ans: Elements can be added to an array using the append(), extend() and the insert (i,x) functions.

Example:

a=arr.array('d', [1.1 , 2.1 ,3.1] )
a.append(3.4)
print(a)
a.extend([4.5,6.3,6.8])
print(a)
a.insert(2,3.8)
print(a)

Output:

array(‘d’, [1.1, 2.1, 3.1, 3.4])

array(‘d’, [1.1, 2.1, 3.1, 3.4, 4.5, 6.3, 6.8])

array(‘d’, [1.1, 2.1, 3.8, 3.1, 3.4, 4.5, 6.3, 6.8])

Q47. How to remove values to a python array?

Ans: Array elements can be removed using pop() or remove() method. The difference between these two functions is that the former returns the deleted value whereas the latter does not.

Example:

a=arr.array('d', [1.1, 2.2, 3.8, 3.1, 3.7, 1.2, 4.6])
print(a.pop())
print(a.pop(3))
a.remove(1.1)
print(a)

Output:

4.6

3.1

array(‘d’, [2.2, 3.8, 3.7, 1.2])

Q48. Does Python have OOps concepts?

Ans: Python is an object-oriented programming language. This means that any program can be solved in python by creating an object model. However, Python can be treated as procedural as well as structural language.

Q49. What is the difference between deep and shallow copy?

Ans: Shallow copy is used when a new instance type gets created and it keeps the values that are copied in the new instance. Shallow copy is used to copy the reference pointers just like it copies the values. These references point to the original objects and the changes made in any member of the class will also affect the original copy of it. Shallow copy allows faster execution of the program and it depends on the size of the data that is used.

Deep copy is used to store the values that are already copied. Deep copy doesn’t copy the reference pointers to the objects. It makes the reference to an object and the new object that is pointed by some other object gets stored. The changes made in the original copy won’t affect any other copy that uses the object. Deep copy makes execution of the program slower due to making certain copies for each object that is been called.

Q50. How is Multithreading achieved in Python?

Ans: 

1. Python has a multi-threading package but if you want to multi-thread to speed your code up, then it’s usually not a good idea to use it.
2. Python has a construct called the Global Interpreter Lock (GIL). The GIL makes sure that only one of your ‘threads’ can execute at any one time. A thread acquires the GIL, does a little work, then passes the GIL onto the next thread.
3. This happens very quickly so to the human eye it may seem like your threads are executing in parallel, but they are really just taking turns using the same CPU core.
4. All this GIL passing adds overhead to execution. This means that if you want to make your code run faster then using the threading package often isn’t a good idea.

Q51. What is the process of compilation and linking in python?

Ans: The compiling and linking allows the new extensions to be compiled properly without any error and the linking can be done only when it passes the compiled procedure. If the dynamic loading is used then it depends on the style that is being provided with the system. The python interpreter can be used to provide the dynamic loading of the configuration setup files and will rebuild the interpreter.

The steps that are required in this as:

1. Create a file with any name and in any language that is supported by the compiler of your system. For example file.c or file.cpp
2. Place this file in the Modules/ directory of the distribution which is getting used.
3. Add a line in the file Setup.local that is present in the Modules/ directory.
4. Run the file using spam file.o
5. After a successful run of this rebuild the interpreter by using the make command on the top-level directory.
6. If the file is changed then run rebuildMakefile by using the command as ‘make Makefile’.

Q52. What are Python libraries? Name a few of them.

Python libraries are a collection of Python packages. Some of the majorly used python libraries are – Numpy, Pandas, Matplotlib, Scikit-learn and many more.

Q53. What is split used for?

The split() method is used to separate a given string in Python.

Example:

a="edureka python"
print(a.split())

Output:  [‘edureka’, ‘python’]

Q54. How to import modules in python?

Modules can be imported using the import keyword.  You can import modules in three ways-

Example:

import array           #importing using the original module name
import array as arr    # importing using an alias name
from array import *    #imports everything present in the array module

OOPS Interview Questions

Q55. Explain Inheritance in Python with an example.

Ans: Inheritance allows One class to gain all the members(say attributes and methods) of another class. Inheritance provides code reusability, makes it easier to create and maintain an application. The class from which we are inheriting is called super-class and the class that is inherited is called a derived / child class.

They are different types of inheritance supported by Python:

1. Single Inheritance – where a derived class acquires the members of a single super class.
2. Multi-level inheritance – a derived class d1 in inherited from base class base1, and d2 are inherited from base2.
3. Hierarchical inheritance – from one base class you can inherit any number of child classes
4. Multiple inheritance – a derived class is inherited from more than one base class.

Q56. How are classes created in Python? 

Ans: Class in Python is created using the class keyword.

Example:

class Employee:
def __init__(self, name):
self.name = name
E1=Employee("abc")
print(E1.name)

Output: abc

Q57. What is monkey patching in Python?

Ans: In Python, the term monkey patch only refers to dynamic modifications of a class or module at run-time.

Consider the below example:

# m.py
class MyClass:
def f(self):
print "f()"

We can then run the monkey-patch testing like this:

import m
def monkey_f(self):
print "monkey_f()"

m.MyClass.f = monkey_f
obj = m.MyClass()
obj.f()

The output will be as below:

monkey_f()

As we can see, we did make some changes in the behavior of f() in MyClass using the function we defined, monkey_f(), outside of the module m.

Q58. Does python support multiple inheritance?

Ans: Multiple inheritance means that a class can be derived from more than one parent classes. Python does support multiple inheritance, unlike Java.

Q59. What is Polymorphism in Python?

Ans: Polymorphism means the ability to take multiple forms. So, for instance, if the parent class has a method named ABC then the child class also can have a method with the same name ABC having its own parameters and variables. Python allows polymorphism.

Q60. Define encapsulation in Python?

Ans: Encapsulation means binding the code and the data together. A Python class in an example of encapsulation.

Q61. How do you do data abstraction in Python?

Ans: Data Abstraction is providing only the required details and hiding the implementation from the world. It can be achieved in Python by using interfaces and abstract classes.

Q62.Does python make use of access specifiers?

Q63. How to create an empty class in Python? 

class a:
    pass
obj=a()
obj.name="xyz"
print("Name = ",obj.name)

Output: 

Name =  xyz

Q64. What does an object() do?

Basic Python Programs

Q65. Write a program in Python to execute the Bubble sort algorithm.

def bs(a):             # a = name of list
    b=len(a)-1         # minus 1 because we always compare 2 adjacent values
                             
    for x in range(b):
        for y in range(b-x):
            if a[y]>a[y+1]:
                a[y],a[y+1]=a[y+1],a[y]
    return a
a=[32,5,3,6,7,54,87]
bs(a)

Output:  [3, 5, 6, 7, 32, 54, 87]

Q66. Write a program in Python to produce Star triangle.

def pyfunc(r):
    for x in range(r):
        print(' '*(r-x-1)+'*'*(2*x+1))    
pyfunc(9)

Output:

        *
       ***
      *****
     *******
    *********
   ***********
  *************
 ***************
*****************

Q67. Write a program to produce Fibonacci series in Python.

# Enter number of terms needed                   #0,1,1,2,3,5....
a=int(input("Enter the terms"))
f=0                                         #first element of series
s=1                                         #second element of series
if a<=0:
    print("The requested series is
",f)
else:
    print(f,s,end=" ")
    for x in range(2,a):
        next=f+s                           
        print(next,end=" ")
        f=s
        s=next</pre>

Output: Enter the terms 5 0 1 1 2 3

Q68. Write a program in Python to check if a number is prime.

a=int(input("enter number"))     
if a>1:
    for x in range(2,a):
        if(a%x)==0:
            print("not prime")
            break
    else:
        print("Prime")
else:
    print("not prime")

Output:

enter number 3

Prime

Q69. Write a program in Python to check if a sequence is a Palindrome.

a=input("enter sequence")
b=a[::-1]
if a==b:
    print("palindrome")
else:
    print("Not a Palindrome")

Output:

enter sequence 323 palindrome

Q70. Write a one-liner that will count the number of capital letters in a file. Your code should work even if the file is too big to fit in memory.

Ans:  Let us first write a multiple line solution and then convert it to one-liner code.

with open(SOME_LARGE_FILE) as fh:
count = 0
text = fh.read()
for character in text:
    if character.isupper():
count += 1

We will now try to transform this into a single line.

count sum(1 for line in fh for character in line if character.isupper())

Q71. Write a sorting algorithm for a numerical dataset in Python.

Ans: The following code can be used to sort a list in Python:

list = ["1", "4", "0", "6", "9"]
list = [int(i) for i in list]
list.sort()
print (list)

Q72. Looking at the below code, write down the final values of A0, A1, …An.

A0 = dict(zip(('a','b','c','d','e'),(1,2,3,4,5)))
A1 = range(10)A2 = sorted([i for i in A1 if i in A0])
A3 = sorted([A0[s] for s in A0])
A4 = [i for i in A1 if i in A3]
A5 = {i:i*i for i in A1}
A6 = [[i,i*i] for i in A1]
print(A0,A1,A2,A3,A4,A5,A6)

Ans: The following will be the final outputs of A0, A1, … A6

A0 = {'a': 1, 'c': 3, 'b': 2, 'e': 5, 'd': 4} # the order may vary
A1 = range(0, 10) 
A2 = []
A3 = [1, 2, 3, 4, 5]
A4 = [1, 2, 3, 4, 5]
A5 = {0: 0, 1: 1, 2: 4, 3: 9, 4: 16, 5: 25, 6: 36, 7: 49, 8: 64, 9: 81}
A6 = [[0, 0], [1, 1], [2, 4], [3, 9], [4, 16], [5, 25], [6, 36], [7, 49], [8, 64], [9, 81]]

Python Libraries Interview Questions

Q73. Explain what Flask is and its benefits?

Ans: Flask is a web microframework for Python based on “Werkzeug, Jinja2 and good intentions” BSD license. Werkzeug and Jinja2 are two of its dependencies. This means it will have little to no dependencies on external libraries.  It makes the framework light while there is a little dependency to update and fewer security bugs.

A session basically allows you to remember information from one request to another. In a flask, a session uses a signed cookie so the user can look at the session contents and modify. The user can modify the session if only it has the secret key Flask.secret_key.

Q74. Is Django better than Flask?

Ans: Django and Flask map the URL’s or addresses typed in the web browsers to functions in Python. 

Flask is much simpler compared to Django but, Flask does not do a lot for you meaning you will need to specify the details, whereas Django does a lot for you wherein you would not need to do much work. Django consists of prewritten code, which the user will need to analyze whereas Flask gives the users to create their own code, therefore, making it simpler to understand the code. Technically both are equally good and both contain their own pros and cons.

Q75. Mention the differences between Django, Pyramid and Flask.

Ans: 

• Flask is a “microframework” primarily build for a small application with simpler requirements. In flask, you have to use external libraries. Flask is ready to use.
• Pyramid is built for larger applications. It provides flexibility and lets the developer use the right tools for their project. The developer can choose the database, URL structure, templating style and more. Pyramid is heavy configurable.
• Django can also be used for larger applications just like Pyramid. It includes an ORM.

Q76. Discuss Django architecture.

Ans: Django MVT Pattern:

Figure:  Python Interview Questions – Django Architecture

The developer provides the Model, the view and the template then just maps it to a URL and Django does the magic to serve it to the user.

Q77. Explain how you can set up the Database in Django.

Ans: You can use the command edit mysite/setting.py, it is a normal python module with module level representing Django settings.

Django uses SQLite by default; it is easy for Django users as such it won’t require any other type of installation. In the case your database choice is different that you have to the following keys in the DATABASE ‘default’ item to match your database connection settings.

• Engines: you can change the database by using ‘django.db.backends.sqlite3’ , ‘django.db.backeneds.mysql’, ‘django.db.backends.postgresql_psycopg2’, ‘django.db.backends.oracle’ and so on
• Name: The name of your database. In the case if you are using SQLite as your database, in that case, database will be a file on your computer, Name should be a full absolute path, including the file name of that file.
• If you are not choosing SQLite as your database then settings like Password, Host, User, etc. must be added.

Django uses SQLite as a default database, it stores data as a single file in the filesystem. If you do have a database server—PostgreSQL, MySQL, Oracle, MSSQL—and want to use it rather than SQLite, then use your database’s administration tools to create a new database for your Django project. Either way, with your (empty) database in place, all that remains is to tell Django how to use it. This is where your project’s settings.py file comes in.

We will add the following lines of code to the setting.py file:

DATABASES = {
     'default': {
          'ENGINE' : 'django.db.backends.sqlite3',
          'NAME' : os.path.join(BASE_DIR, 'db.sqlite3'),
     }
}

Q78. Give an example how you can write a VIEW in Django?

Ans: This is how we can use write a view in Django:

from django.http import HttpResponse
import datetime

def Current_datetime(request):
     now = datetime.datetime.now()
     html = "<html><body>It is now %s</body></html> % now
     return HttpResponse(html)

Returns the current date and time, as an HTML document

Q79. Mention what the Django templates consist of.

Ans: The template is a simple text file.  It can create any text-based format like XML, CSV, HTML, etc.  A template contains variables that get replaced with values when the template is evaluated and tags (% tag %) that control the logic of the template.

Figure: Python Interview Questions – Django Template

Q80. Explain the use of session in Django framework?

Ans: Django provides a session that lets you store and retrieve data on a per-site-visitor basis. Django abstracts the process of sending and receiving cookies, by placing a session ID cookie on the client side, and storing all the related data on the server side.

Figure: Python Interview Questions – Django Framework

So the data itself is not stored client side. This is nice from a security perspective.

Q81.  List out the inheritance styles in Django.

Ans: In Django, there are three possible inheritance styles:

1. Abstract Base Classes: This style is used when you only want parent’s class to hold information that you don’t want to type out for each child model.
2. Multi-table Inheritance: This style is used If you are sub-classing an existing model and need each model to have its own database table.
3. Proxy models: You can use this model, If you only want to modify the Python level behavior of the model, without changing the model’s fields.

Web Scraping – Python Interview Questions

Q82. How To Save An Image Locally Using Python Whose URL Address I Already Know?

Ans: We will use the following code to save an image locally from an URL address

import urllib.request
urllib.request.urlretrieve("URL", "local-filename.jpg")

Q83. How can you Get the Google cache age of any URL or web page?

Ans: Use the following URL format:

http://webcache.googleusercontent.com/search?q=cache:URLGOESHERE

Be sure to replace “URLGOESHERE” with the proper web address of the page or site whose cache you want to retrieve and see the time for. For example, to check the Google Webcache age of edureka.co you’d use the following URL:

http://webcache.googleusercontent.com/search?q=cache:edureka.co

Q84. You are required to scrap data from IMDb top 250 movies page. It should only have fields movie name, year, and rating.

Ans: We will use the following lines of code:

from bs4 import BeautifulSoup

import requests
import sys

url = 'http://www.imdb.com/chart/top'
response = requests.get(url)
soup = BeautifulSoup(response.text)
tr = soup.findChildren("tr")
tr = iter(tr)
next(tr)

for movie in tr:
title = movie.find('td', {'class': 'titleColumn'} ).find('a').contents[0]
year = movie.find('td', {'class': 'titleColumn'} ).find('span', {'class': 'secondaryInfo'}).contents[0]
rating = movie.find('td', {'class': 'ratingColumn imdbRating'} ).find('strong').contents[0]
row = title + ' - ' + year + ' ' + ' ' + rating

print(row)

The above code will help scrap data from IMDb’s top 250 list

Data Analysis – Python Interview Questions

Q85. What is map function in Python?

Ans: map function executes the function given as the first argument on all the elements of the iterable given as the second argument. If the function given takes in more than 1 arguments, then many iterables are given. #Follow the link to know more similar functions.

Q86. Is python numpy better than lists?

Ans: We use python numpy array instead of a list because of the below three reasons:

1. Less Memory
2. Fast
3. Convenient

For more information on these parameters, you can refer to this section – Numpy Vs List.

Q87. How to get indices of N maximum values in a NumPy array?

Ans: We can get the indices of N maximum values in a NumPy array using the below code:

import numpy as np
arr = np.array([1, 3, 2, 4, 5])
print(arr.argsort()[-3:][::-1])

Output

[ 4 3 1 ]

Q88. How do you calculate percentiles with Python/ NumPy?

Ans: We can calculate percentiles with the following code

import numpy as np
a = np.array([1,2,3,4,5])
p = np.percentile(a, 50) #Returns 50th percentile, e.g. median
print(p)

Output

3

Q89. What is the difference between NumPy and SciPy?

Ans: 

1. In an ideal world, NumPy would contain nothing but the array data type and the most basic operations: indexing, sorting, reshaping, basic elementwise functions, et cetera.
2. All numerical code would reside in SciPy. However, one of NumPy’s important goals is compatibility, so NumPy tries to retain all features supported by either of its predecessors.
3. Thus NumPy contains some linear algebra functions, even though these more properly belong in SciPy. In any case, SciPy contains more fully-featured versions of the linear algebra modules, as well as many other numerical algorithms.
4. If you are doing scientific computing with python, you should probably install both NumPy and SciPy. Most new features belong in SciPy rather than NumPy.

Q90. How do you make 3D plots/visualizations using NumPy/SciPy?

Ans: Like 2D plotting, 3D graphics is beyond the scope of NumPy and SciPy, but just as in the 2D case, packages exist that integrate with NumPy. Matplotlib provides basic 3D plotting in the mplot3d subpackage, whereas Mayavi provides a wide range of high-quality 3D visualization features, utilizing the powerful VTK engine.

Multiple Choice Questions (MCQ)

Q91. Which of the following statements create a dictionary? (Multiple Correct Answers Possible)

a) d = {}
b) d = {“john”:40, “peter”:45}
c) d = {40:”john”, 45:”peter”}
d) d = (40:”john”, 45:”50”)

Answer: b, c & d. 

Dictionaries are created by specifying keys and values.

Q92. Which one of these is floor division?

a) /
b) //
c) %
d) None of the mentioned

Answer: b) //

When both of the operands are integer then python chops out the fraction part and gives you the round off value, to get the accurate answer use floor division. For ex, 5/2 = 2.5 but both of the operands are integer so answer of this expression in python is 2. To get the 2.5 as the answer, use floor division using //. So, 5//2 = 2.5

Q93. What is the maximum possible length of an identifier?

a) 31 characters
b) 63 characters
c) 79 characters
d) None of the above

Answer: d) None of the above

Identifiers can be of any length.

Q94. Why are local variable names beginning with an underscore discouraged?

a) they are used to indicate a private variables of a class
b) they confuse the interpreter
c) they are used to indicate global variables
d) they slow down execution

Answer: a) they are used to indicate a private variable of a class

As Python has no concept of private variables, leading underscores are used to indicate variables that must not be accessed from outside the class.

Q95. Which of the following is an invalid statement?

a) abc = 1,000,000
b) a b c = 1000 2000 3000
c) a,b,c = 1000, 2000, 3000
d) a_b_c = 1,000,000

Answer: b) a b c = 1000 2000 3000

Spaces are not allowed in variable names.

Q96. What is the output of the following?

try:
    if '1' != 1:
        raise "someError"
    else:
        print("someError has not occured")
except "someError":
    print ("someError has occured")

a) someError has occured
b) someError has not occured
c) invalid code
d) none of the above

Answer: c) invalid code

A new exception class must inherit from a BaseException. There is no such inheritance here.

Q97. Suppose list1 is [2, 33, 222, 14, 25], What is list1[-1] ?

a) Error
b) None
c) 25
d) 2

Answer: c) 25

The index -1 corresponds to the last index in the list.

Q98. To open a file c:scores.txt for writing, we use

a) outfile = open(“c:scores.txt”, “r”)
b) outfile = open(“c:scores.txt”, “w”)
c) outfile = open(file = “c:scores.txt”, “r”)
d) outfile = open(file = “c:scores.txt”, “o”)

Answer: b) The location contains double slashes ( ) and w is used to indicate that file is being written to.

Q99. What is the output of the following?

f = None

for i in range (5):
    with open("data.txt", "w") as f:
        if i > 2:
            break

print f.closed

a) True
b) False
c) None
d) Error

Answer: a) True 

The WITH statement when used with open file guarantees that the file object is closed when the with block exits.

Q100. When will the else part of try-except-else be executed?

a) always
b) when an exception occurs
c) when no exception occurs
d) when an exception occurs into except block

Answer: c) when no exception occurs

The else part is executed when no exception occurs.

I hope this set of Python Interview Questions will help you in preparing for your interviews. All the best!

Got a question for us? Please mention it in the comments section and we will get back to you at the earliest.

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