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Java OOPs Interview Questions to Crack Coding Interviews

by Interview Kickstart Team in Interview Questions
December 8, 2021

Java OOPs Interview Questions to Crack Coding Interviews

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Java OOPs interview questions revolve around Object-Oriented Programming, also known as OOPs. It refers to a set of languages in programming that use the concept of objects and classes. Java’s OOPs concepts, such as abstraction, encapsulation, inheritance, and polymorphism, make Java one of the most widely used programming languages in the industry.

Software engineers skilled in Java and OOPs concepts are always in high demand. According to Indeed, Java Developers have the lowest career switch rate of all professions. 

So, let’s get you started on your Java OOPs interview preparation! If you’re a software engineer, coding engineer, software developer, engineering manager, or tech lead preparing for tech interviews, check out our technical interview checklist, interview questions page, and salary negotiation ebook to get interview-ready! 

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In this article, we will cover:

  • OOPs Concepts in Java Interview Questions
  • Java OOPs Interview Questions
  • FAQs on Java OOP Interview

OOPs Concepts in Java Interview Questions

OOP connects data and functions that operate on them so that no other part of the code can access the data except that function. While most programmers are accustomed to top-down programming, Java OOPs is a step forward in tech democratization because it is built on these pillars. It is critical that you thoroughly understand these OOP features because they are the basis for most Java OOPs interview questions. Let's go over the fundamental Java OOP concepts:

Encapsulation

One of the most significant benefits of OOP is that data is hidden from other parts of a language and is placed in a capsule. OOP is involved in encapsulating data by default. Ideally, objects will contain both the data and the methods that affect data. A good OOP practice will mean that you offer getter and setter methods to control data access. Mutable data is protected from being changed and makes application data much safer.

Inheritance

Objects can be created as subtypes of other objects. This is done by inheriting methods and variables from the said objects. This way, objects can support operations defined by anterior types without needing a definition of their own.

Polymorphism

Like shape-changing, Java OOP allows one object or method to become a template for another object or method. Single functions can become overloaded, shift shapes and adapt to the related class. Java OOPs have been very successful because the tech industry supports and is supported by OOP.

Data Abstraction

It displays important information and hides the details of implementation.

Take a look at the most popular back-end development languages you should learn to get a job at FAANG companies.

Top Java OOPs Interview Questions

You need to practice core Java interview questions on OOPs concepts to answer basic Java OOP interview questions. Most Java OOP interview questions will be based on OOP concepts such as encapsulation, polymorphism, inheritance, data abstraction, classes and objects, methods and functions, and exception handling. 

Here are a few sample Java OOP interview questions from each category.

Core Java OOPs Interview Questions and Answers

1. What is Object-Oriented Programming in Java?

OOP entails real-life entities such as a pencil, television, or a bank account. The basic condition is that this entity should possess a state (for data) and behavior (for method). Using access, specifiers secure access to this data and methods. You can hide data and provide access to specific essentials using encapsulation and data abstraction. 

With the help of polymorphism and inheritance, one can reuse code and help overload or override methods. This results in platform-independent applications that are secure and robust.

2. Name some widely used OOP languages.

The most widely used OOP languages are C++, C#, Python, Java, Go, Dart, and Ruby.

3. Is Java purely Object-Oriented?

Java is not entirely an object-oriented programming language. This is because Java still uses primitive data types like float, int, double, char, etc. These data types are stored as stacks and not on the heap. Java also allows static methods to access static variables without using an object.

4. What is Class and Object in Java?

Class is a template used to create objects. It has a state and behavior supported by an Object. This Object is an instance of the said Class. You can think of Class as a human. The state of this human will be factors such as its digestive system, eye color, and age. Its behavior will include things like canEat(), ableToSmell(), and many more.

More Sample Interview Questions for Java OOP Developers

  1. Where does the need for object-oriented programming arise?
  2. What is an Interface?
  3. Explain the difference between extends and implements.
  4. Name the different access modifiers in Java.
  5. What is the difference between constructor and method?
  6. What is a constructor?
  7. What are the types of constructors in Java?
  8. Why/when is a new keyword used?
  9. What types of arguments can be used in Java?
  10. When would you use the super keyword?
  11. Name the object-oriented features used in Java.
  12. Describe the main features of OOPs.
  13. List down some limitations of OOPs.
  14. Differentiate between structural and object-oriented programming.
  15. What is a pure object-oriented language?
  16. Explain procedural programming in OOP.
  17. Differentiate between error and exception.
  18. Explain the concept of composition.
  19. What is Coupling in OOPs?

Your Java OOPs interview prep is incomplete without practicing coding problems. Check out these coding interview questions and answers.

Interview Questions on Features of Java OOPs 

  1. Describe Data Abstraction with an example
  2. Give some real-time examples to explain Inheritance.
  3. What are the types of inheritance?
  4. How does polymorphism work in Java?
  5. What are the advantages of Abstraction and Inheritance?
  6. Differentiate between Compile-time Polymorphism and Runtime.
  7. Differentiate between dynamic and static binding.
  8. Differentiate between Inheritance and Composition.
  9. Explain the concept of manipulators in OOP.
  10. Which operators cannot overload?

Java OOPs Interview Questions on Classes and Objects

  1. Differentiate between Class and Object in Java.
  2. What is the difference between method and abstract class?
  3. Describe base class, subclass, and superclass.
  4. Explain the characteristics of abstract class.
  5. Can a class inherit the constructor of its base class?
  6. Differentiate between class and structure.
  7. Explain the concept of access specifiers.
  8. State the rules for creating a constructor.
  9. Differentiate between assignment operator and copy constructor.
  10. Explain constructor chaining.

Java OOP Interview Questions on Methods and Functions

  1. Explain method overloading.
  2. Describe method overriding.
  3. Explain the concept of constructor overloading.
  4. Does Java support operator overloading?
  5. When would you use the finalize method?
  6. Explain the concept of Tokens.
  7. What is the basic difference between the method and the constructor in Java?

OOPs Interview Questions and Answers in Java for Experienced Engineers

Here are some Java OOPs interview questions for 5 years experience holding candidates:

  1. Is Polymorphism supported in Java?
  2. How much memory is occupied by a class?
  3. Do you always need to create objects from class?
  4. Name the types of constructors in Java.
  5. How is an interface different from an abstract class?
  6. What is exception handling?
  7. What is Garbage Collection in OOPs?
  8. Can a Java application be run without the implementation of OOPs?

FAQs on Java OOPs Interview Questions

Q1. How much does a Java OOP Developer earn?
A. According to Indeed, the average compensation for a Java Developer is $100,200 per year in the United States, along with a $5,000 bonus per year. 

Q2. Is Java developer a good career?
Tech hiring stats dropped initially in 2020 but bounced back quickly by year-end. According to CompTIA, 391,000 new tech positions were added in the US in December 2020. Among these, the largest share of 62,900 postings was for software developers and application developers. As far as job satisfaction is concerned, according to Glassdoor's Best Jobs in America 2021 Survey, Java Developers ranked 1 in the US with a job satisfaction rating of 4.2 out of 5!

Q3. Which companies use Java OOP to build their products?
A. According to Stackshare, 9915 companies, use Java in their tech stacks. Here are the top companies that use Java: Netflix, Uber, Airbnb, Google, Pinterest, Instagram, Spotify, Amazon, Slack, Spring, and more.

Q4. What are the top skills required to become a Java Developer?
A. The top skills in demand these days in a Java Developer are: Software Design and Architecture, Microservices, DevOps Tools, React or Angular, JUnit and Mockito, Design Patterns, Spring Boot, Learn APIs, and JVM Internals.

Q5. What are some Java OOP concept interview questions?

The primary Java OOPs concepts are encapsulation, abstraction, inheritance, and polymorphism. Some of the java interview questions on these concepts are: What is a superclass? What is inheritance? What is hierarchical inheritance? What is polymorphism? What is method overloading? What is encapsulation? What is the difference between public, private, and protected access modifiers? How to achieve data abstraction? What is an exception? What is exception handling?

Prepare for Your Next Java OOPs Interview With Interview Kickstart

Ready to crack your next Java OOPs interview? Register for IK’s webinar today to learn how to leverage exclusive interview preparation courses and mock interviews with experts.

Interview Kickstart has helped over 9,000 engineers land coveted offers from FAANG and tier-1 companies. Our instructors are technical leads and hiring managers at FAANG and know exactly what it takes to crack big tech interviews.

Want to learn more? Sign up for our FREE webinar on How to Nail Your Next Tech Interview.


WEBINAR +LIVE Q&A

How To Nail Your Next Tech Interview

Hosted By
Ryan Valles
Founder, Interview Kickstart
Our tried & tested strategy for cracking interviews
How FAANG hiring process works
The 4 areas you must prepare for
How you can accelerate your learnings

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