Java Object-Oriented Programming – OOP Concepts with Examples

What are OOP Concepts?

Object-oriented programming (OOP) is a programming paradigm based on the concept of objects, which can contain data and behavior. Java is an object-oriented language and follows the OOP principles. Understanding OOP concepts is crucial for any Java developer as it helps in writing efficient, scalable, and maintainable code.

Top 5 Concepts

1. Classes and Objects

A class is a blueprint for creating objects. It defines the variables and methods that an object will contain. An object is an instance of a class. In Java, every object belongs to a class and an object is created using the ’new‘ operator.


2. Inheritance

Inheritance is the process of creating a new class from an existing class. The new class inherits all the properties and methods of the existing class. This helps in creating a hierarchy of classes and makes code reusable. In Java, inheritance is achieved by using the ‚extends‘ keyword. You cannot inherit from multiple classes at once like in other languages.


3. Polymorphism

Polymorphism in general means „many forms“. It occurs when you have many classes that are related to each other by inheritance. But how do you do it? Polymorphism in Java is done through method overloading and method overriding.

Method overloading refers to having two or more methods with the same name but different parameters, while method overriding refers to having two methods with the same name, parameters, and return type in a subclass and its superclass.

Here is an example of method overloading:


As you can see, the class Calculator has two methods with the same name ‚add‘, but with different parameters. One time with double, the other method takes integers as arguments. When you call the add method, Java will determine which method to call based on the parameters you pass.

4. Abstraction

Abstraction is the process of hiding the implementation details and exposing only the necessary information to the user. In Java, abstraction is achieved through interfaces and abstract classes. An interface defines a set of abstract methods that must be implemented by any class that implements the interface. An abstract class is a class that contains one or more abstract methods and cannot be instantiated.
In general, prefer composition over inheritance.

5. Encapsulation

Encapsulation is the process of binding data and functions together in a single unit, known as an object. It helps in keeping the data and behavior of an object safe from outside interference. In Java, encapsulation is achieved through access modifiers like ‚private‘, ‚protected‘, and ‚public‘. Always use as much encapsulation as possible. Never be scared of creating an object. It makes code much more readable in my opinion


It’s important to note that OOP is not the only programming paradigm, and it’s not always the best choice for every problem. However, for many applications, OOP provides a natural and intuitive way to model real-world objects and their relationships.

In the end, the choice of whether to use OOP or another paradigm depends on the specific requirements of the project and the personal preferences of the programmer. Regardless of the choice, it’s essential to have a solid understanding of OOP concepts, as they are widely used in many programming languages, including Java.

In conclusion, OOP is a powerful programming paradigm that allows developers to write efficient, scalable, and maintainable code. By mastering the five core concepts of OOP in Java, you will be well-equipped to write robust and high-quality software applications.

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