php设计模式之单例模式的例子。
 

复制代码 代码示例:

<?php
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class Fruit {   
    private static $instanceMap = array();
    //protected getter for singleton instances
protected static function getSingleton($className)
{
   //保证单例模式 并且不能从控制器实例化和克隆
   if(!isset(self::$instanceMap[$className]))
   {
       $object = new $className;
       //Make sure this object inherit from Singleton
       if($object instanceof Fruit)
    {   
           self::$instanceMap[$className] = $object;
           var_dump($object);
        }
            else
    {
                throw SingletonException("Class '$className' do not inherit from Singleton!");
            }
        }
        return self::$instanceMap[$className];
    }   
   
    //protected constructor to prevent outside instantiation
    protected function __construct(){
    }
   
    //denie cloning of singleton objects
    public final function __clone(){
        trigger_error('It is impossible to clone singleton', E_USER_ERROR);
    }   
}

class Apple extends Fruit {   
    protected $rndId;
   
    public function __construct(){
        $this->rndId = rand();
    }   
   
    public function whatAmI(){
        echo 'I am a Apple('.$this->rndId.')<br />';
    }
    public static function getInstance(){
   //echo get_class();
        return Fruit::getSingleton(get_class());
    }
}
class GreenApple extends Apple {
    public function whatAmI(){
        echo 'I am a GreenApple('.$this->rndId.')<br />';
    }
   
    public static function getInstance(){
        return Fruit::getSingleton(get_class());
    }
}
$apple1 = Apple::getInstance();
//var_dump($apple1);
$apple2 = GreenApple::getInstance();
$apple1->whatAmI();// should echo 'I am a Apple(some number)
$apple2->whatAmI();// should echo 'I am a GreenApple(some number)
$apple1 = Apple::getInstance();
$apple2 = GreenApple::getInstance();
//保证单例模式
$apple1->whatAmI();// should echo 'I am a Apple(same number as above)
$apple2->whatAmI();// should echo 'I am a GreenApple(same number as above)
// $a = clone $apple1;// this should fail
// $b = clone $apple2;// this should fail
?>