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。

  1 package com.tiger.practice;
  2 
  3  class Shape {
  4     
  5     public double length(){
  6         return 0;
  7     }
  8     
  9     public double area() {
 10         return 0;
 11     }
 12 }
 13  
 14  class Rectangle extends Shape {
 15 
 16         private double width;
 17         private double height;
 18 
 19 
 20         public Rectangle(double height,double width) {
 21             this.height=height;
 22             this.width = width;
 23         }
 24 
 25         @Override
 26         public double length() {
 27             // TODO Auto-generated method stub
 28             return 2*(width+height);
 29         }
 30 
 31         @Override
 32         public double area() {
 33             // TODO Auto-generated method stub
 34             return width*height;
 35         }
 36 
 37         public double differ() {
 38             return Math.abs(height-width);
 39         }
 40 
 41     }
 42  
 43  class Square extends Rectangle {
 44     
 45      public double edge;
 46  
 47      public Square(double edge) {
 48          super(edge,edge);
 49          setEdge(edge);
 50          // TODO Auto-generated constructor stub
 51      }
 52 
 53      public double getEdge() {
 54          return edge;
 55      }
 56  
 57      public void setEdge(double edge) {
 58          this.edge = edge;
 59      }  
 60  }
 61  
 62  class Triangle extends Shape {
 63         private double a;
 64         private double b;
 65         private double c;
 66         
 67         public Triangle(double a,double b,double c) {
 68             this.a= a;
 69             this.b = b;
 70             this.c = c;
 71         }
 72 
 73         @Override
 74         public double length() {
 75             // TODO Auto-generated method stub
 76             return a+b+c;
 77         }
 78 
 79         @Override
 80         public double area() {
 81             double p= (a+b+c)/2;
 82             // TODO Auto-generated method stub
 83             return Math.sqrt(p*(p-a)*(p-b)*(p-c));
 84         }
 85     }
 86  
 87  class circle extends Shape{
 88      private double r;
 89      public circle(double r){
 90          this.r = r;
 91      }
 92      public double length(){
 93          return 3.1415*2*r;
 94      }
 95      public double area(){
 96          return 3.1415*r*r;
 97      }
 98      
 99  }
100 
101 public class shapes {
102 
103     /**
104      * @param args
105      */
106     public static void main(String[] args) {
107         // TODO Auto-generated method stub
108         Shape[] shapes= {
109                 new Rectangle(5,10),
110                 new circle(5),
111                 new Square(3),
112                 new Triangle(3, 4, 5)
113             };
114         for(int i=0;i<shapes.length;i++) {
115             double length=shapes[i].length();
116             double area=shapes[i].area();
117             if(shapes[i]instanceof circle) {
118                 System.out.println("Shape("+(i+1)+"): "+
119                         "length"+String.format("%.4f", length)+",area"
120                         +String.format("%.4f", area));
121             }
122             else {
123                         System.out.println("Shape("+(i+1)+"): "+
124                             "length"+length+",area"+area);
125                     if(shapes[i]instanceof Rectangle) {
126                         Rectangle r=(Rectangle)shapes[i];
127                         System.out.println("长宽差是:   "+r.differ());
128                     }
129             }
130         }
131     }
132 
133 }