code: public DateTime toDateTime(DateTimeZone zone) {
          Chronology chrono = DateTimeUtils.getChronology(getChronology());
          chrono = chrono.withZone(zone);
          return new DateTime(getMillis(), chrono);
      }
docs: Get this object as a DateTime using the same chronology but a different zone.
  
  @param zone time zone to apply, or default if null
  @return a DateTime using the same millis