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!
";
    }
}



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



?>