code: private synchronized ZNames loadTimeZoneNames(String tzID) {
          ZNames tznames = _tzNamesMap.get(tzID);
          if (tznames == null) {
              ZNamesLoader loader = new ZNamesLoader();
              loader.loadTimeZone(_zoneStrings, tzID);
              tznames = ZNames.createTimeZoneAndPutInCache(_tzNamesMap, loader.getNames(), tzID);
          }
          return tznames;
      }
docs: Returns a set of names for the given time zone ID. This method loads
  the set of names into the internal map and trie for future references.
  @param tzID the canonical time zone ID
  @return An instance of ZNames that includes a set of time zone display names.