Top OOPs Java Interview Questions 2023

Prepare for your OOPs Java interview Questions with our comprehensive list of interview questions and ace your interview.

Table of Contents

Commonly Asked OOPs Java Interview Questions

Let’s discuss some of the commonly asked OOPs Java Interview Questions.

What is Object-Oriented Programming (OOP)?

The Object-Oriented Programming (OOP) paradigm organizes software design around “objects,” which are instances of classes. OOP emphasizes encapsulation, inheritance, and polymorphism to organize code, improve reusability, and effectively model real-world things.

What are the Four Pillars of OOPs?

The four pillars of OOPs are:

Encapsulation: Encapsulation involves bundling data (attributes) and methods (functions) that operate on that data into a single unit, known as a class. It restricts direct access to data, promoting data integrity.
Inheritance: Inheritance enables the creation of new classes based on existing classes. It allows the derived class (subclass) to inherit properties and behaviors from the base class (superclass), promoting code reuse.
Polymorphism: Polymorphism refers to the ability of different classes to be treated as instances of a common superclass. It allows a single interface to represent multiple implementations, improving flexibility and extensibility.
Abstraction: Abstraction involves simplifying complex reality by modeling classes based on essential attributes and behaviors. It hides unnecessary details, allowing developers to focus on high-level functionalities.

Explain the Concept of Class in Java.

A class is a blueprint or template in object-oriented programming (OOP) that determines the structure and behavior of objects. It acts as a template for producing objects, which are actual instances of the class. A class encapsulates data (attributes or properties) and methods that operate on that data (functions or behaviors).

For example, if you were modeling a “Car” in a software application, you could include properties like “make,” “model,” and “color,” as well as functions like “startEngine,” “accelerate,” and “brake.” Each instance of the “Car” class represents a unique automobile object, complete with its own set of attribute values and the ability to perform the given methods.

What is the Role of Constructor?

Constructors are Java methods that are used to initialize class objects. They make certain that objects are correctly initialized before being used. Constructors can be overloaded to give additional methods for creating instances of a class.

Explain the Concept of Interface in Java.

In Java, an interface defines a contract that classes must follow. It defines a set of methods that must be provided by implementing classes. By allowing a class to implement numerous interfaces, interfaces enable multiple inheritance-like behavior. They are essential for attaining code modularity and loose coupling.

Explain the Concept of Abstract Classes.

In Java, an abstract class is one that cannot be instantiated on its own. It serves as a template for other classes and may have abstract methods (methods that do not have implementations). Abstract class subclasses must offer concrete implementations of abstract methods. Abstract classes allow you to establish shared behaviour among subclasses.

Inheritance vs Composition vs Aggregation

Please read this article Inheritance vs Composition vs Aggregation for detailed answer.

Static Binding vs Dynamic Binding

Binding is a process of associating a method call with the proper method body.

We can distinguish two types of binding in Java: static and dynamic.

The main difference between static binding and dynamic binding is that static binding occurs at compile time and dynamic binding at runtime.

Static binding uses class information for binding. It’s responsible for resolving class members that are private or static and final methods and variables.
Also, static binding binds overloaded methods.

Dynamic binding, on the other hand, uses object information to resolve bindings. That’s why it’s responsible for resolving virtual and overridden methods.

Please read Polymorphism in Java for more details.

Compile time polymorphism vs Run time polymorphism

Please read Polymorphism in Java for detailed answer.

what are the rules for method overloading and method overriding?

Please read Polymorphism in Java for detailed answer.

Conclusion: OOPs Java Interview Questions

In this article we discussed some of the most commonly asked OOPs Java interview questions.These OOPs Java interview questions and answers are intended to provide you with a firm foundation in Object-Oriented Programming concepts in Java. By learning these, you will be well-prepared to face Java interviews with confidence.