Shape接口：

/**  * @version V 1.0  * @Descriptyion :  * @Author:hsfxuebao  * @Date 2018/3/14 20:09  * @Modified By :  */ public interface Shape {  double area(double radius); }

Circle类：

public class Circle implements Shape {   @Override  public double area(double radius) {  return Math.PI * radius * radius;  } }
Square类：

public class Square implements Shape {  @Override  public double area(double radius) {  return radius * radius;  } }

测试方法：

public class TestShape {   public static void main(String[] args) {  Shape circle = new Circle();  Shape square = new Square();  int number = 2;  int radius = 3;  //计算正方形的面积  System.out.println(square.area(number));  //计算圆形的面积  System.out.println(circle.area(radius));   } }

运行结果：

4.0
28.274333882308138