Abstract class in JAVA

 abstract class Shape {

    abstract double area(); // Abstract method to calculate area

    abstract double perimeter(); // Abstract method to calculate perimeter

    void display() {

        System.out.println("This is a shape.");

    }

}

class Circle extends Shape {

    double radius;

    Circle(double radius) {

        this.radius = radius;

    }

    @Override

    double area() {

        return Math.PI * radius * radius;

    }

    @Override

    double perimeter() {

        return 2 * Math.PI * radius;

    }

}

class Rectangle extends Shape {

    double length;

    double width;

    Rectangle(double length, double width) {

        this.length = length;

        this.width = width;

    }

    @Override

    double area() {

        return length * width;

    }

    @Override

    double perimeter() {

        return 2 * (length + width);

    }

}

public class AbstractClassExample {

    public static void main(String[] args) {

        Circle circle = new Circle(5);

        System.out.println("Area of circle: " + circle.area());

        System.out.println("Perimeter of circle: " + circle.perimeter());

        Rectangle rectangle = new Rectangle(4, 6);

        System.out.println("Area of rectangle: " + rectangle.area());

        System.out.println("Perimeter of rectangle: " + rectangle.perimeter());

        circle.display();

        rectangle.display();

    }

}