public static function getInstance() { if (empty(self::$instance)) { self::$instance = new self(); } return self::$instance; }
public static function getInstance() { //判断self::$instance 是否已经被实例化 if (!self::$instance instanceof self) { self::$instance = new self(); } return self::$instance; }
public final function __destruct() { self::$instance = null; }