<?php
//單例模式
class Site{
//屬性
public $siteName;
//本類的靜態例項
private static $instance = null;
//禁用構造方法
private function __construct($siteName){
$this->siteName=$siteName;
}
//克隆方法私有化
private function __clone(){}
//生成當前類的唯一例項
public static function getInstance($siteName='PHP中文網'){
if(!self::$instance instanceof self
 
){
self::$instance=new self($siteName);
}
return self::$instance;
}
   }
//用工廠模式來生成本類的單一例項
class Factory{
//建立指定類的例項
public static function create($siteName){
return Site::getInstance($siteName);
}
   }
//物件註冊樹
/**
   * 1.註冊:set(),把物件掛在樹上
   * 2.獲取:get(),把物件取下來
   * 3.登出:_unset():把物件吃掉
   */
class Register{
 
//建立物件池
protected static $objects=[];
//生成物件並上樹
public static function set($alias,$object){
self::$objects[$alias] = $object;
}
//衝樹上面取下物件
public static function get($alias){
return self::$objects[$alias];
}
//把樹上的物件吃掉
public static function _unset($alias){
unset(self::$objects[$alias]);
}
   }
//將Site類的例項上樹，放入物件池
 
Register::set('site',Factory::create('www.php.cn'));
//從樹上取下一個物件下來
$obj=Register::get('site');
var_dump($obj);