interface Shape {  double area(double a);   } class Square implements Shape{   public double area(double a) {      return a*a;       }} class Circle implements Shape{   public double area(double a) {      return 3.14159*a*a;       }} public class tt {     public static void main(String [] args){         Shape a=new Square();         Shape b=new Circle();         calarea(a,2);         calarea(b,3);     }     public static void calarea(Shape shape,double c){         System.out.println(shape.area(c));     } }