What Are the Principles of Object Oriented Programming in Java?


Angela Bailey

Object-oriented programming (OOP) is a programming paradigm that revolves around the concept of objects. In Java, one of the most popular programming languages, OOP principles are at the core of its design.

Understanding these principles is essential for writing clean and maintainable code. In this article, we will explore the key principles of object-oriented programming in Java.

1. Encapsulation

Encapsulation is one of the fundamental principles of OOP.

It refers to the bundling of data and methods that operate on that data into a single unit called an object. Encapsulation provides data hiding, which means that the internal state and implementation details of an object are hidden from other objects. This enhances security and ensures that objects can only be accessed through well-defined interfaces.

2. Inheritance

Inheritance allows classes to inherit properties and behaviors from other classes. It promotes code reuse by enabling the creation of new classes based on existing ones.

In Java, inheritance is achieved using the ‘extends’ keyword. The subclass inherits all public and protected members (fields and methods) from its superclass. This principle facilitates hierarchical organization and promotes code extensibility.

3. Polymorphism

Polymorphism refers to the ability of objects to take on multiple forms or types. In Java, polymorphism is achieved through method overriding and method overloading.

  • Method Overriding: Subclasses can provide their own implementation for methods defined in their superclass.
  • Method Overloading: Multiple methods with the same name but different parameters can coexist in a class.

This principle allows for code flexibility, as objects can be treated as instances of their own class or any of their parent classes.

4. Abstraction

Abstraction focuses on representing essential features of an object while hiding unnecessary details.

It allows for the creation of abstract classes and interfaces that define a common interface for a group of related objects. Abstract classes cannot be instantiated but can be extended by other classes.

5. Composition

Composition is a principle that allows objects to be composed of other objects as part of their state.

This is achieved through the use of instance variables that refer to other objects. Composition enables code reuse by creating complex objects from simpler ones, promoting modularity and flexibility in design.

6. Association

Association represents a relationship between two or more objects, where each object has its own lifecycle and there is no ownership between them.

It can be either one-to-one, one-to-many, or many-to-many. Associations are typically implemented through the use of instance variables that reference other objects.


In this article, we have explored the key principles of object-oriented programming in Java – encapsulation, inheritance, polymorphism, abstraction, composition, and association. Understanding these principles is crucial for writing clean and modular code that can be easily maintained and extended.

Note: Remember to practice these principles in your Java projects to leverage the power of object-oriented programming and enhance your coding skills.

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