Java Abstract keyword

The abstract keyword in Java is used to define abstract classes and methods. It plays a key role in achieving abstraction in object-oriented programming, allowing you to define methods without implementation and enforce implementation by subclasses.

Abstract Class:

An abstract class is a class declared with the abstract keyword. It:

Can include abstract methods (methods without implementation) and concrete methods (methods with implementation).
Cannot be instantiated (you cannot create objects of an abstract class).
Serves as a blueprint for subclasses.

Syntax:

abstract class ClassName {
    // Abstract method (no implementation)
    abstract void abstractMethod();


    // Concrete method (with implementation)
    void concreteMethod() {
        System.out.println("This is a concrete method.");
    }
}

Example

abstract class Animal {

// Abstract method

abstract void sound();

// Concrete method

void eat() {

System.out.println("This animal eats food.");

}

class Dog extends Animal {

void sound() {

System.out.println("Dog barks.");

}

public class Main {

public static void main(String[] args) {

Animal myDog = new Dog();

myDog.sound(); // Calls the overridden method

myDog.eat(); // Calls the inherited concrete method

}

Try it yourself

Abstract Methods:

An abstract method:

Is declared using the abstract keyword.
Does not have a body (implementation).
Must be implemented by any concrete subclass of the abstract class.

Example

abstract class Shape {

abstract void draw(); // Abstract method

}

class Circle extends Shape {

void draw() {

System.out.println("Drawing a Circle.");

}

class Rectangle extends Shape {

void draw() {

System.out.println("Drawing a Rectangle.");

}

public class Main {

public static void main(String[] args) {

Shape shape1 = new Circle();

shape1.draw();

Shape shape2 = new Rectangle();

shape2.draw();

}

Try it yourself

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