code: private TimeZoneNames getTZDBTimeZoneNames() {
          if (_tzdbNames == null) {
              synchronized(this) {
                  if (_tzdbNames == null) {
                      _tzdbNames = new TZDBTimeZoneNames(_locale);
                  }
              }
          }
          return _tzdbNames;
      }
docs: Private method returning the instance of TZDBTimeZoneNames.
  The instance if used only for parsing when {@link ParseOption#TZ_DATABASE_ABBREVIATIONS}
  is enabled.
  @return an instance of TZDBTimeZoneNames.