Define an abstract class Shape with an abstract method area(). Write a Java program to calculate the area of a circle and a sphere

// Abstract class Shape

abstract class Shape {

    abstract double area();

}

// Circle class extending Shape

class Circle extends Shape {

    private double radius;

// Constructor

    public Circle(double radius) {

        this.radius = radius; //old variable = new variable

    }

     double area() {

        return Math.PI * radius * radius; // Area of Circle = πr²

    }

}

class Sphere extends Shape {

    private double radius;

    public Sphere(double radius) {

        this.radius = radius;

    }

     double area() {

        return 4 * Math.PI * radius * radius; // Surface Area of Sphere = 4πr²

    }

}

public class ShapeTest {

    public static void main(String[] args) {

        Circle circle = new Circle(5);  

        Sphere sphere = new Sphere(5);  

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

        System.out.println("Sphere Area: " + sphere.area());

    }

}