protected function parseCrontab( $crontab )
    {
        $lines = preg_split( '(\r\n|\r|\n)', $crontab );
        $this->crontab = array();
        foreach ( $lines as $line )
        {
            $line = trim( $line );
            if ( !empty( $line ) &&
                 ( $line[0] !== '#' ) &&
                 ( $line[0] !== ';' ) )
            {
                $this->crontab[] = new Cronjob( $line );
            }
        }
    }