interface Shape{     public double area(double a); } class Square implements Shape{     @Override     public double area(double a) {         return a*a;     } } class Circle implements Shape{     @Override     public double area(double a) {         return Math.PI*a*a;     } } public class NowerCoder {     public static void main(String[] args) {         Shape circle = new Circle();         System.out.printf("%.2f",circle.area(2.0));         System.out.println();         Shape square = new Square();         System.out.printf("%.2f",square.area(2.0));     } }