package com.nowcoder.interfaces; // 提供计算几何形状面积方法的接口 interface Shape{ double area(double d); } // 正方形类 class Square implements Shape{ public double area(double length) { if(length < 0) throw new RuntimeException("边长不能为负数！"); return length*length; } } // 圆形类 class Circle implements Shape{ public double area(double radius) { if(radius < 0) throw new RuntimeException("半径不能为负数！"); return Math.PI*radius*radius; } } //测试类 public class Test { // 计算Shape面积的多态方法 public static double area(Shape shape, double d) { return shape.area(d); } public static void main(String[] args) { System.out.println("边长为2的正方形面积为："+area(new Square(), 2)); System.out.println("半径为3的圆形面积为："+area(new Circle(), 3)); } }