private function __validateNumeric($int, $minLength = 1, $maxLength = 0)
    {
        if (!is_numeric($int)) {
            $this->error = 'parameter is not number';
            return false;
        } else if ($maxLength > 0 && strlen($int) > $maxLength) {
            $this->error = 'parameter is too long. number:' . $int;
            return false;
        } else if (strlen($int) < $minLength) {
            $this->error = 'parameter is too short. number:' . $int;
            return false;
        }
        return true;
    }