<?php 
   //abstract root class 抽象根类 
   abstract class Shape 
   { 
       abstract function getArea(); //定义一个抽象方法 
   } 

   //abstract child class 抽象子类 
   abstract class Polygon extends Shape //多边形 
   { 
       abstract function getNumberOfSides(); 
   } 

   //concrete class 实体类 三角形类 
   class Triangle extends Polygon 
   { 
       public $base; 
       public $height; 

       public function getArea() //覆写计算面积方法 
       { 
           return(($this->base * $this->height)/2); 
       } 

       public function getNumberOfSides() //覆写边数统计方法 
       { 
           return(3); 
       } 
   } 

   //concrete class 实体类四边形 
   class Rectangle extends Polygon 
   { 
       public $width; 
       public $height; 

       public function getArea() 
       { 
           return($this->width * $this->height); 
       } 

       public function getNumberOfSides() 
       { 
           return(4); 
       } 
   } 

   //concrete class 实体类 圆形 
   class Circle extends Shape 
   { 
       public $radius; 

       public function getArea() 
       { 
           return(pi() * $this->radius * $this->radius); 
       } 
   } 

   //concrete root class 定义一个颜色类 
   class Color 
   { 
       public $name; 
   } 

   $myCollection = array(); //建立形状的集合,放入数组 

   //make a rectangle 
   $r = new Rectangle; 
   $r->width = 5; 
   $r->height = 7; 
   $myCollection[] = $r; 
   unset($r); 

   //make a triangle 
   $t = new Triangle; 
   $t->base = 4; 
   $t->height = 5; 
   $myCollection[] = $t; 
   unset($t); 

   //make a circle 
   $c = new Circle; 
   $c->radius = 3; 
   $myCollection[] = $c; 
   unset($c); 

   //make a color 
   $c = new Color; 
   $c->name = "blue"; 
   $myCollection[] = $c; 
   unset($c); 

   foreach($myCollection as $s) 
   { 
       if($s instanceof Shape) //如果$s是Shape类的实例 
       { 
           print("Area: " . $s->getArea() . 
               "<br>\n"); 
       } 

       if($s instanceof Polygon) 
       { 
           print("Sides: " . 
               $s->getNumberOfSides() . 
               "<br>\n"); 
       } 

       if($s instanceof Color) 
       { 
           print("Color: $s->name<br>\n"); 
       } 

       print("<br>\n"); 
   } 

?> 

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