php模式设计

1，策略模式

2，个体模式

3，工厂模式

4，观察者模式

 <?php
 class ExchangeRate
 {
     static private $instance = NULL;
     private $observers = array();
     private $exchange_rate;

     static function getInstance()
     {
         if (self::$instance == NULL)
             self::$instance = new ExchangeRate();
         return self::$instance;
     }
     public function registerObserver($obj)
     {
         $this->observers[] = $obj;
     }
     public function getExchangeRate()
     {
         return $this->exchange_rate;
     }
     public function setExchangeRate($new_rate)
     {
         $this->exchange_rate = $new_rate;
         $this->notifyObservers();

     }
     function notifyObservers()
     {
         foreach ($this->observers as $obj) {
             # code...
             $obj->notify($this);
         }
     }

 }

 class ProductItem
 {
     public function __construct()
     {
         ExchangeRate::getInstance()->registerObserver($this);

     }
     public function notify($obj)
     {
         if($obj instanceof ExchangeRate) print "Received update!\n";
     }
 }

 $a = new ProductItem();
 $b = new ProductItem();
 ExchangeRate::getInstance()->setExchangeRate(4.5);

 ?>