基于php设计模式中单例模式的应用分析

<?php
class DanLi{
    //静态成员变量
    private static $_instance;
    //私有的构造方法
    private function __construct(){
    }
    //防止对象被克隆
    public function __clone(){
        trigger_error(‘Clone is not allow!‘,E_USER_ERROR);
    }
    public static function getInstance(){
        if(!(self::$_instance instanceof self)){
            self::$_instance = new self;
        }
        return self::$_instance;
    }
    public function test(){
        echo "ok";
    }
}

//错误：$danli = new DanLi(); $danli_clone = clone $danli;
//正确：$danli = DanLi::getInstance(); $danli->test();

?>