private function generateHash()
    {
        $this->hash = hash('md5', serialize(array(
            strval($this->getMinute()),
            strval($this->getHour()),
            strval($this->getDayOfMonth()),
            strval($this->getMonth()),
            strval($this->getDayOfWeek()),
            strval($this->getCommand()),
        )));

        return $this;
    }