code: protected function newInstance(Map $fields)
      {
          $year  = $fields->get(self::$YEAR);
          $month = $fields->get(self::$MONTH);
          $date  = $fields->get(self::$DATE);
          return new self($year, $month, $date);
      }
docs: (non-PHPdoc)
  @return Date
  @see Time::newInstance
  @ignore