实验四 （1）：定义一个形状类（Shape）方法：计算周长，计算面积

（1）定义一个形状类（Shape）方法：计算周长，计算面积
子类：
矩形类（Rectangle） ：额外的方法：differ（） 计算长宽差
圆形类（Circle）
三角形类（Triangle）
正方形类（Square） 矩形的子类
生成几个不同的形状对象，放在一个Shape类型的数组里，分别求每个形状的周长和面积。如果形状对象是一个矩形，且不是正方形，则计算长宽差。

 package com.tiger.practice;

  class Shape {

     public double length(){
         return ;
     }

     public double area() {
         return ;
     }
 }

  class Rectangle extends Shape {

         private double width;
         private double height;

         public Rectangle(double height,double width) {
             this.height=height;
             this.width = width;
         }

         @Override
         public double length() {
             // TODO Auto-generated method stub
             return *(width+height);
         }

         @Override
         public double area() {
             // TODO Auto-generated method stub
             return width*height;
         }

         public double differ() {
             return Math.abs(height-width);
         }

     }

  class Square extends Rectangle {

      public double edge;

      public Square(double edge) {
          super(edge,edge);
          setEdge(edge);
          // TODO Auto-generated constructor stub
      }

      public double getEdge() {
          return edge;
      }

      public void setEdge(double edge) {
          this.edge = edge;
      }
  }

  class Triangle extends Shape {
         private double a;
         private double b;
         private double c;

         public Triangle(double a,double b,double c) {
             this.a= a;
             this.b = b;
             this.c = c;
         }

         @Override
         public double length() {
             // TODO Auto-generated method stub
             return a+b+c;
         }

         @Override
         public double area() {
             double p= (a+b+c)/;
             // TODO Auto-generated method stub
             return Math.sqrt(p*(p-a)*(p-b)*(p-c));
         }
     }

  class circle extends Shape{
      private double r;
      public circle(double r){
          this.r = r;
      }
      public double length(){
          return 3.1415**r;
      }
      public double area(){
          return 3.1415*r*r;
      }

  }

 public class shapes {

     /**
      * @param args
      */
     public static void main(String[] args) {
         // TODO Auto-generated method stub
         Shape[] shapes= {
                 new Rectangle(,),
                 new circle(),
                 new Square(),
                 new Triangle(, , )
             };
         for(int i=;i<shapes.length;i++) {
             double length=shapes[i].length();
             double area=shapes[i].area();
             if(shapes[i]instanceof circle) {
                 System.out.println("Shape("+(i+)+"): "+
                         "length"+String.format("%.4f", length)+",area"
                         +String.format("%.4f", area));
             }
             else {
                         System.out.println("Shape("+(i+)+"): "+
                             "length"+length+",area"+area);
                     if(shapes[i]instanceof Rectangle) {
                         Rectangle r=(Rectangle)shapes[i];
                         System.out.println("长宽差是:   "+r.differ());
                     }
             }
         }
     }

 }