public class TestMain {          public static void main(String[]args) {         double length = 2;//正方形长度         double breadth = 2; //正方形宽度         double r = 3; //圆的半径         double PI = 3.14;         Square Sqacreage = new Square();         Circle Ciacreage = new Circle();                  System.out.println("正方形的面积为:"+Sqacreage.area(length,breadth));              System.out.print("圆的面积为:"+Ciacreage.area(r, PI ));     }               /**      *       * @Shape接口      *      */     interface Shape{         public abstract double area(double length,double breadth);     }          /**      *       * @Square class 计算正方形面积      *      */     static class Square implements Shape{         public double area(double length,double breadth) {             return length*breadth;         }     }          /**      * @Circle class 计算圆的面积      */          static class Circle implements Shape{         public double area(double r,double PI) {             PI = 3.14;             return PI*r*r;         }     } }