public static function getInstance($dbuser = DB_USER, $dbpassword = DB_PASSWORD, $dbname = DB_NAME, $dbhost = DB_HOST,$flag )
    {

        self::$amount++;
        if (self::$amount <=2 && !array_key_exists($flag, self::$tab)) {
            var_dump($flag);
            self::$_instance = new self($dbuser, $dbpassword, $dbname, $dbhost);
            self::$tab[]=[$flag => self::$_instance];
            var_dump(self::$tab);
        }
        return self::$tab[$flag];
    }