OOPs in Java & 4 Pillars of OOPs, Advantages & Why It Matters

Last Updated on April 11, 2026 by Rex

OOPs in Java: If we talk about Java, the most important concept we need to know is OOPs. OOPs helps you to write clean, Organized and scalable code. Why “oops” is better than procedural is given

What is OOPs in Java

OOPs stands for Object-Oriented Programming. It is a Java programming paradigm that focuses on creating objects that contain both data and behavior. Before starting the pillar of OOP, first we have to know about classes and objects.

Class

A class is a blueprint or, say, template of an object. It represents the set of properties or methods. Class is a logical entity. It is declared with the keyword class. And it does not take memory, but the object takes it when created.

Object

An object is an instance of a class. It is created with the class, holds the property values, and can use the methods. An object is a real entity, not logical like a class. It takes memory when it is created. In short, we say class is the template, and the object is the thing made from that template. A home is made from a map. Just like that, the home map is a class, and the home is a real entity,, like an object. It is created using a new keyword.

Benefits of Object-Oriented Programming:

There are many Benefits of OOPs, like

1. Modularity
2. Code reusability
3. Improved security
4. Flexible
5. Scalable
6. Maintainable

Pillars of Object-Oriented Programming:-

The main four pillars of object-oriented programming are as follows:

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

1-Encapsulation

The binding of the data and methods together inside the single unit, i.e., class, is called encapsulation. It helps in hiding the internal data and accessing it by using getter and setter methods. It is also known as data hiding. It is used for security reasons.

Access Modifier

The four access modifiers are as follows: –

Advantage and Disadvantage Of Encapsulation

2-Abstraction

To hide the internal implementation and show only the necessary things is called abstraction. For example: Switching on the fan no matter what—to know the mechanism of the fan and its working. It is one of the most important pillars of the oops.
In Java we can achieve abstraction with abstract classes and interfaces.

Advantage and Disadvantage Of Abstraction

Inheritance

Inheritance means to pass the properties and methods of the parent class to its child class. For example, in real life, children inherit properties from their parents, such as some of your traits matching your father’s.

This is the parent class
class Vehicle {
String color = “Black”;
int wheels = 4;

void start() {
System.out.println(“Vehicle is starting…”);
}
}

This is the Child Class which inherit the Vehicle class using extend keyword
class Car extends Vehicle {
String model = “Sedan”;

void showDetails() {
System.out.println(“Color: ” + color);
System.out.println(“Wheels: ” + wheels);
System.out.println(“Model: ” + model);
}
}

Types of Inheritance

The types of inheritance and differences are given below: –

Advantage and Disadvantage Of Inheritance

PolyMorphism

Polymorphism is made up of two Greek words. Poly=many, morph=forms. That allows objects to behave differently based on their specific class type. This means it can take multiple forms.

Types of PolyMorphism

1. Compile-Time Polymorphism
2. Runtime Polymorphism

Advantage and Disadvantage Of Polymorphism

Common Interview Questions

1- What is OOP in Java?

OOP in Java stands for Object-Oriented Programming, which is a programming approach that uses classes and objects to structure code. It helps in making applications modular, reusable, and easy to maintain. Java follows four main OOP principles: encapsulation, abstraction, inheritance, and polymorphism. These concepts help developers build scalable and secure applications.

2- Tell me how abstraction and encapsulation are different.

Abstraction means hiding implementation details and showing only essential functionality to the user, while encapsulation means wrapping data and methods together and protecting data using access modifiers like private and public. In simple terms, abstraction focuses on what to show, and encapsulation focuses on how to protect data.

3- What is method overloading?

Method overloading is a feature in Java where multiple methods have the same name but different parameters in the same class. It helps improve code readability and allows methods to perform different operations based on input. It is also known as compile-time polymorphism because the method call is resolved during compilation.

4- What is method overriding?

Method overriding is when a child class provides its own implementation of a method that is already defined in the parent class. It is used to achieve runtime polymorphism and allows dynamic method execution based on the object. The method name and parameters must be the same as the parent class method.

5- What is inheritance?

Inheritance is a concept in Java where one class acquires the properties and methods of another class using the extends keyword. It helps in code reusability and reduces duplication. For example, a dog class can inherit common behavior like eat() from an animal class.

6- Can Java support multiple inheritance?

Java does not support multiple inheritance with classes to avoid the diamond problem, which creates ambiguity in method calls. However, Java supports multiple inheritance using interfaces, where a class can implement multiple interfaces and inherit their methods.

7- What is polymorphism?

Polymorphism means one method behaving in multiple ways depending on the object. In Java, it is achieved using method overloading and method overriding. Overloading provides compile-time polymorphism, and overriding provides runtime polymorphism, making the code flexible and dynamic.

8- Is Java a pure OOP? Why?

No, Java is not a pure object-oriented language because it supports primitive data types like int, float, and boolean, which are not objects. In pure OOP languages, everything is treated as an object, but Java uses both objects and primitive types, so it is considered partially object-oriented.

For official documentation, see Oracle Java Tutorials

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