java用接口、多态、继承、类计算三角形和矩形周长及面积的方法

/**  * @author vvv  * @date 2013-8-10 上午08:56:48  */ package com.duotai; /**  *  *  */ public interface Shape {   public double area();   public double longer(); } /**  * @author vvv  * @date 2013-8-10 上午09:10:06  */ package com.duotai; /**  *  *  */ public class Triangle implements Shape {   double s1;   double s2;   double s3;   // 初始化一个三角形对象，并赋予该三角形三边长   public Triangle(double s1, double s2, double s3) {     if (isTri(s1, s2, s3)) {       this.s1 = s1;       this.s2 = s2;       this.s3 = s3;     } else {       System.out.println("输入的三边长" + s1 + "、" + s2 + "、" + s3      + "不能组成一个三角形，请重新输入三边长！");     }   }   // 判断是否是个三角形   public boolean isTri(double s1, double s2, double s3) {     if (s1 + s2 < s3) {       return false;     }     if (s1 + s3 < s2) {       return false;     }     if (s2 + s3 < s1) {       return false;     }     return true;   }   /*    * (non-Javadoc)    *    * @see com.duotai.Shape#area()    */   @Override   public double area() {     double p = (s1 + s2 + s3) / 2;     return Math.sqrt(p * (p - s1) * (p - s2) * (p - s3));   }   /*    * (non-Javadoc)    *    * @see com.duotai.Shape#longer()    */   @Override   public double longer() {     return s1 + s2 + s3;   } } /**  * @author vvv  * @date 2013-8-10 上午09:12:06  */ package com.duotai; /**  *  *  */ public class Director implements Shape {   double s1;   double s2;   // 初始化一个长方形，并赋予该长方形两边长   public Director(double s1, double s2) {     this.s1 = s1;     this.s2 = s2;   }   /*    * (non-Javadoc)    *    * @see com.duotai.Shape#area()    */   @Override   public double area() {     // TODO Auto-generated method stub     return s1 * s2;   }   /*    * (non-Javadoc)    *    * @see com.duotai.Shape#longer()    */   @Override   public double longer() {     // TODO Auto-generated method stub     return 2 * (s1 + s2);   } } /**  * @author vvv  * @date 2013-8-10 上午09:13:30  */ package com.duotai; /**  *  *  */ public class Test {   /**    * @param args    */   public static void main(String[] args) {     Shape triangle = new Triangle(3, 4, 8);    // 新建一个三边长为3，4，5的三角形     Shape tri = new Triangle(3, 4, 5);     Shape director = new Director(10, 20);    // 新建一个两边长为10,20的长方形     System.out.println("三角形triangle的周长为：" + triangle.longer());     System.out.println("三角形triangle的面积为：" + triangle.area());     System.out.println("三角形tri的周长为：" + tri.longer());     System.out.println("三角形tri的面积为：" + tri.area());     System.out.println("该长方形的周长为：" + director.longer());     System.out.println("该长方形的面积为：" + director.area());   } }