Program to calculate area using abstract class in Java

import java.lang.Math;
abstract class Shape
{
abstract void area();
double area;
}
class Rectangle extends Shape
{
double w=50,h=25;
void area()
{
area = w*h;
System.out.println("Area of Rectangle : "+area);
}
}
class Square extends Shape
{
double a=40;
void area()
{
area = (a*a);
System.out.println("Area of Square : "+area);
}
}
class Circle extends Shape
{
double r=7;
void area()
{
area = Math.PI * r * r;
System.out.println("Area of Circle : "+area);
}
}
class calculate_area
{
public static void main(String [] args)
{
Square sq= new Square();
Rectangle rc =new Rectangle();
Circle cr =new Circle();
sq.area();
rc.area();
cr.area();
}
}

 

Output: