php单例模式示例分享

<?
     class mysql{
        privete static $instance ;//保存实例
         //构造函数声明为private， 防止直接创建对象
        privete function __construct(){
             // 实例化
         }
         //单例方法， 判断是否已经实例化，只实例化一次
         public static function getInstance (){
             if(!isset( self::$instance )){
                self ::$instance = new self();
             }
             return self:: $instance;
         }
         //防止克隆对象
         private function __clone (){
             trigger_error ("not allow to clone.");
         }
         function test(){
             echo "test" ;
         }
     }
     $conn = mysql::getInstance ();
     $conn->test ();
?>