Java Abstraction Explained with Examples

What is Abstraction in Java?

Abstraction is a fundamental concept in object-oriented programming (OOP) that focuses on hiding the internal details and showing only the essential features of an object. In Java, abstraction allows you to define the behavior of an object without exposing the implementation details. This approach enhances modularity, code maintainability, and security.

Abstraction in Java can be achieved using abstract classes and interfaces.

Key Benefits of Abstraction

Reduces Complexity: Simplifies the programming process by focusing only on relevant operations.
Improves Code Security: Sensitive implementation details are hidden from the end user.
Promotes Reusability: Abstract methods and interfaces enable code reusability across multiple classes.
Enhances Maintainability: Makes it easier to update or modify code since changes to internal logic don’t affect external functionality.

How to Achieve Abstraction in Java

Abstraction is implemented in Java through:

Abstract Classes
Interfaces

1. Abstract Classes

An abstract class in Java is a class that cannot be instantiated. It can contain abstract methods (methods without a body) and concrete methods (methods with a body). Abstract classes are used when multiple classes share common behavior but need to implement specific features in their own way.

Syntax of Abstract Class

abstract class Shape {
    abstract void draw(); // Abstract method
    void display() {      // Concrete method
        System.out.println("This is a shape");
    }
}

Example of Abstract Class

abstract class Shape {
    abstract void draw(); // Abstract method

    void display() { // Concrete method
        System.out.println("Drawing a shape...");
    }
}

class Circle extends Shape {
    @Override
    void draw() {
        System.out.println("Drawing a Circle");
    }
}

class Rectangle extends Shape {
    @Override
    void draw() {
        System.out.println("Drawing a Rectangle");
    }
}

public class Main {
    public static void main(String[] args) {
        Shape circle = new Circle();
        circle.display();
        circle.draw();

        Shape rectangle = new Rectangle();
        rectangle.draw();
    }
}

Output:

Drawing a shape...
Drawing a Circle
Drawing a Rectangle

2. Interfaces

An interface in Java is a blueprint of a class. It contains only abstract methods by default (until Java 8). Interfaces are implemented by classes, and a class can implement multiple interfaces, allowing multiple inheritance.

Syntax of Interface

interface Animal {
    void sound(); // Abstract method
}

Example of Interface

interface Animal {
    void sound(); // Abstract method
}

class Dog implements Animal {
    @Override
    public void sound() {
        System.out.println("Dog barks");
    }
}

class Cat implements Animal {
    @Override
    public void sound() {
        System.out.println("Cat meows");
    }
}

public class Main {
    public static void main(String[] args) {
        Animal dog = new Dog();
        dog.sound();

        Animal cat = new Cat();
        cat.sound();
    }
}