Java OOPs Top Interview Questions and Answers in 2025
Java is object oriented and here we are covering oops interview questions and answers. Java inherits features of C++. OOP features of java are influenced by C++. OOP concept forms the heart of java language that helps java program in survive the inevitable changes accompanying software development.
TechShitanshu has prepared a list of the top OOPs interview questions and answers that are frequently asked in the interview. It is going to help you to crack the interview to get your dream job.
Certainly, here are some common oops interview questions that might come up during a job interview. These questions can help the interviewer gauge your qualifications, experience, and fit for the role. Be prepared to answer these questions with confidence:
Blog is divided into 2 different sections, they are :
OOPs Basic Interview Questions
1. Provide a concise definition and explain the key principles of OOP.
Answer: OOP is a way of writing computer programs using objects, which are like building blocks. Objects have data and functions that can work with that data. It’s a way to model real-world things and their interactions in code.
2. How do you create an object in OOP?
Answer: In Object-Oriented Programming (OOP), you create an object by following these steps:
Define a Class: First, you need to define a class. A class is like a blueprint that defines the structure and behavior of objects. It specifies the attributes (data) and methods (functions) that objects created from this class will have.
Instantiate the Class: To create an object, you need to use the class as a template. This is done by instantiating the class, which means you’re creating a specific instance of that class. You do this by calling the class’s constructor method.
Use the Object: Once the object is created, you can use it to access its attributes and methods. You can manipulate the object and perform various operations based on the class’s defined behavior.
3. Describe encapsulation, inheritance, polymorphism, and abstraction.
Answer: Encapsulation is also a part of the OOPs concept. It refers to the bundling of data with the methods that operate on that data. It also helps to restrict any direct access to some of an object’s components.
Inheritance is a feature of OOPs which allows classes inherit common properties from other classes. For example, if there is a class such as ‘vehicle’, other classes like ‘car’, ‘bike’, etc can inherit common properties from the vehicle class. This property helps you get rid of redundant code thereby reducing the overall size of the code.
Polymorphism is one of the most used and core concepts in OOP languages. It explains the concept of different classes can be used with the same interface. Each of these classes can have its own implementation of the interface.
Abstraction is an OOPs concept to build the structure of real-world objects. It “shows” only essential attributes and “hides” unnecessary information from the outside. The main focus of abstraction is to hide unnecessary details from the users. It is one of the most important concepts of OOPs.
4. What are classes and objects in OOP?
Answer: Classes are like blueprints for creating objects. They define the structure and behavior of objects. Objects, on the other hand, are instances of classes, meaning they are actual things created based on those blueprints.
5. Why to use OOPs?
Answer:
- Code can be reused through inheritance thereby reducing redundancy
- OOPs allows clarity in programming thereby allowing simplicity in solving complex problems
- Data and code are bound together by encapsulation
- OOPs allows data hiding, therefore, private data is kept confidential
- Problems can be divided into different parts making it simple to solve
- The concept of polymorphism gives flexibility to the program by allowing the entities to have multiple forms
OOPs Interview Questions for Experienced
1. What is constructor chaining?
Answer: Constructor chaining is a method to call one constructor from another concerning a current object reference. It can be done in two ways: –
- Using the “this” keyword, the reference can be made to the constructor in the current class.
- To call the constructor from the base class “super” keyword will be used.
2. What are pure virtual functions?
Answer: A popular oops interview questions – A pure virtual function/method is a function whose implementations are not provided in the base class, and only a declaration is provided. The pure virtual function can have its implementation code in the derived class; otherwise, the derived class will also be considered an abstract Class. The Class containing pure virtual functions is abstract.
3. What is the default method of Java 8?
Answer: The default method, also known as the extension method, is a new type of method which you can add to the interface now. These methods have implementation and are intended to be used by default. By using this method, JDK 8 managed to provide common functionality related to lambda expression and stream API without breaking all the clients who implement their interfaces. If you look at Java 8 API documentation you will find several useful default methods on key Java interfaces like Iterator, Map, etc.
4. Can an interface extend more than one interface in Java?
Answer: Yes, an interface can extend more than one interface in Java, it’s perfectly valid.
5. Can a class extend more than one class in Java?
Answer: No, a class can only extend another class because Java doesn’t support multiple inheritances but yes, it can implement multiple interfaces.
🔹 1. What is OOPs in Java?
Answer:
OOPs (Object-Oriented Programming System) is a programming approach where everything revolves around objects and classes. It models real-world entities into code for better organization, reusability, and scalability.
Key principles of OOPs:
Encapsulation
Inheritance
Polymorphism
Abstraction
🔹 2. What are the main features of OOPs in Java?
Answer:
Encapsulation – Binding data and code together inside a class.
Inheritance – Acquiring properties from another class.
Polymorphism – Using one interface for multiple forms (method overloading & overriding).
Abstraction – Hiding implementation details and showing only necessary functionality.
🔹 3. What is a Class in Java?
Answer:
A class is a blueprint or template for creating objects. It defines variables (attributes) and methods (behaviors).
🔹 4. What is an Object in Java?
Answer:
An object is an instance of a class. It represents a real-world entity with state and behavior.
🔹 5. What is Inheritance in Java?
Answer:
Inheritance allows one class to acquire the properties and behaviors of another class using the extends keyword.
🔹 6. What is Polymorphism?
Answer:
Polymorphism means “many forms.” It allows one interface to be used for different data types.
It is of two types:
Compile-time (method overloading)
Runtime (method overriding)
🔹 7. What is Method Overloading in Java?
Answer:
Method Overloading occurs when multiple methods have the same name but different parameters within the same class.
🔹 8. What is Method Overriding?
Answer:
It occurs when a subclass provides its own version of a method already defined in its superclass.
🔹 9. What is Abstraction?
Answer:
Abstraction is hiding complex logic and exposing only the necessary details.
In Java, it can be achieved using abstract classes or interfaces.
🔹 10. What is Encapsulation?
Answer:
Encapsulation is wrapping data (variables) and code (methods) into a single unit, i.e., a class, and controlling access using access modifiers.
🔹 11. What are Access Modifiers in Java?
Answer:
They define the visibility of classes, methods, and variables.
Types:
publicprivateprotected(default)
🔹 12. What is the difference between Abstract Class and Interface?
| Feature | Abstract Class | Interface |
|---|---|---|
| Keyword | abstract | interface |
| Methods | Can have abstract and non-abstract methods | Only abstract methods (until Java 8) |
| Inheritance | Single | Multiple |
| Use Case | Common base with shared logic | Contract-based behavior |
🔹 13. What is a Constructor in Java?
Answer:
A constructor initializes an object when it is created. It has the same name as the class and no return type.
🔹 14. What is the difference between Constructor and Method?
| Feature | Constructor | Method |
|---|---|---|
| Purpose | Initialize object | Perform operation |
| Name | Same as class | Any name |
| Return Type | None | Has a return type |
| Call | Called automatically | Called manually |
🔹 15. What is ‘this’ Keyword in Java?
Answer:this refers to the current object of a class. It helps differentiate between instance variables and parameters with the same name.
🔹 16. What is Super Keyword?
Answer:super is used to call the parent class constructor or access parent class methods and variables.
🔹 17. What is Object Cloning?
Answer:
Object cloning means creating an exact copy of an object using the clone() method of the Object class.
🔹 18. What is the Difference Between Overloading and Overriding?
| Feature | Overloading | Overriding |
|---|---|---|
| Occurs in | Same class | Subclass |
| Parameters | Must differ | Must be same |
| Compile/Runtime | Compile-time | Runtime |
🔹 19. Can a Constructor be Overloaded?
Answer:
Yes ✅. A class can have multiple constructors with different parameter lists (constructor overloading).
🔹 20. What is a Static Method?
Answer:
A static method belongs to the class rather than an instance. It can be called without creating an object.
🔹 21. What is the Difference Between Class and Object?
| Term | Description |
|---|---|
| Class | Blueprint/template |
| Object | Instance of the class |
🔹 22. What is Final Keyword?
Answer:
The final keyword is used to restrict modification:
final variable→ constantfinal method→ cannot be overriddenfinal class→ cannot be extended
🔹 23. What is Multiple Inheritance in Java?
Answer:
Java doesn’t support multiple inheritance with classes to avoid ambiguity but supports it with interfaces.
🔹 24. What is the Difference Between Composition and Inheritance?
Answer:
Inheritance – “is-a” relationship.
Composition – “has-a” relationship (using objects inside another class).
🔹 25. Why is OOPs Important in 2025?
Answer:
With evolving Java frameworks like Spring Boot 3 and Microservices, OOP principles remain the foundation for building scalable, maintainable, and modular software.
Mastering OOPs ensures you stay relevant in every era of Java development.
Leave a Reply to Unlock Top 10 Java Lambda Expressions Interview Questions Cancel reply