The TimeZone class implements a time zone information source for client applications. The time zone object is instantiated from a TimeZoneData object, which is made from a JSON string that contains all the data needed for the specified time zone. Applications can instantiate a time zone statically, in which case the data could be retrieved from the {@link com.google.gwt.i18n.client.constants.TimeZoneConstants TimeZoneConstants} class. Applications can also choose to instantiate from a string obtained from a server. The time zone string contains locale specific data. If the application only uses a short representation, the English data will usually satisfy the user's need. In the case that only the time zone offset is known, there is a decent fallback that only uses the time zone offset to create a TimeZone object.

class TimeZone {
// constants to reference time zone names in the time zone names array
 static final int _STD_SHORT_NAME = 0;
 static final int _STD_LONG_NAME = 1;
 static final int _DLT_SHORT_NAME = 2;
 static final int _DLT_LONG_NAME = 3;

 /**
  * This factory method provides a decent fallback to create a time zone object
  * just based on a given time zone offset.
  *
  * @param timeZoneOffsetInMinutes time zone offset in minutes
  * @return a new time zone object
  */
 static TimeZone createTimeZone(int timeZoneOffsetInMinutes) {
   TimeZone tz = new TimeZone();
   tz._standardOffset = timeZoneOffsetInMinutes;
   tz._timezoneID = _composePOSIXTimeZoneID(timeZoneOffsetInMinutes);
   tz._tzNames = new List<String>(2);
   tz._tzNames[0] = _composeUTCString(timeZoneOffsetInMinutes);
   tz._tzNames[1] = _composeUTCString(timeZoneOffsetInMinutes);
   tz._transitionPoints = null;
   tz._adjustments = null;
   return tz;
 }

 /**
  * This factory method creates a time zone instance from a JSON string that
  * contains the time zone information for desired time zone. Applications can
  * get such a string from the TimeZoneConstants class, or it can request the
  * string from the server. Either way, the application obtains the original
  * string from the data provided in the TimeZoneConstant.properties file,
  * which was carefully prepared from CLDR and Olson time zone database.
  *
  * @param tzJSON JSON string that contains time zone data
  * @return a new time zone object
  */
//  static TimeZone createTimeZoneFromJson(String tzJSON) {
//    TimeZoneInfo tzData = TimeZoneInfo.buildTimeZoneData(tzJSON);
//
//    return createTimeZoneFromInfo(tzData);
//  }

//  static TimeZone createTimeZoneFromInfo(TimeZoneInfo timezoneData) {
//    TimeZone tz = new TimeZone();
//
//    tz._timezoneID = timezoneData.getID();
//    tz._standardOffset = -timezoneData.getStandardOffset();
//
//    List<String> jsTimezoneNames = timezoneData.getNames();
//
//    tz._tzNames = new List<String>(jsTimezoneNames.length);
//
//    for (int i = 0; i < jsTimezoneNames.length; i++) {
//      tz._tzNames[i] = jsTimezoneNames[i];
//    }
//
//    List<int> transitions = timezoneData.getTransitions();
//
//    if (transitions == null || transitions.length == 0) {
//      tz._transitionPoints = null;
//      tz._adjustments = null;
//    } else {
//      int transitionNum = transitions.length ~/ 2;
//      tz._transitionPoints = new List<int>(transitionNum);
//      tz._adjustments = new List<int>(transitionNum);
//
//      for (int i = 0; i < transitionNum; ++i) {
//        tz._transitionPoints[i] = transitions[i * 2];
//        tz._adjustments[i] = transitions[i * 2 + 1];
//      }
//    }
//    return tz;
//  }

 /**
  * In GMT representation, +/- has reverse sign of time zone offset.
  * when offset == 480, it should output GMT-08:00.
  */
 static String _composeGMTString(int offset) {
   List<int> data = 'GMT-00:00'.codeUnits;
   if (offset <= 0) {
     data[3] = '+'.codeUnitAt(0);
     offset = -offset; // suppress the '-' sign for text display.
   }
   data[4] += (offset ~/ 60) ~/ 10;
   data[5] += (offset ~/ 60) % 10;
   data[7] += (offset % 60) ~/ 10;
   data[8] += offset % 10;
   return new String.fromCharCodes(data);
 }

 /**
  * POSIX time zone ID as fallback.
  */
 static String _composePOSIXTimeZoneID(int offset) {
   if (offset == 0) {
     return "Etc/GMT";
   }
   String str;
   if (offset < 0) {
     offset = -offset;
     str = "Etc/GMT-";
   } else {
     str = "Etc/GMT+";
   }
   return str +  _offsetDisplay(offset);
 }

 static String _composeUTCString(int offset) {
   if (offset == 0) {
     return "UTC";
   }
   String str;
   if (offset < 0) {
     offset = -offset;
     str = "UTC+";
   } else {
     str = "UTC-";
   }
   return str +  _offsetDisplay(offset);
 }

 static String _offsetDisplay(int offset) {
   int hour = offset ~/ 60;
   int mins = offset % 60;
   if (mins == 0) {
     return hour.toString();
   }
   return hour.toString() + ":" + mins.toString();
 }

 String _timezoneID;
 int _standardOffset;
 List<String> _tzNames;
 List<int> _transitionPoints;
 List<int>  _adjustments;

 TimeZone() {
 }

 /* (non-Javadoc)
  * @see com.google.gwt.i18n.client.TimeZoneIntf#getDaylightAdjustment(java.util.DateTime)
  */
 int getDaylightAdjustment(DateTime date) {
   if (_transitionPoints == null) {
     return 0;
   }
   int timeInHours = date.millisecond ~/ 1000 ~/ 3600;
   int index = 0;
   while (index < _transitionPoints.length &&
       timeInHours >= _transitionPoints[index]) {
     ++index;
   }
   return (index == 0) ? 0 : _adjustments[index - 1];
 }

 /* (non-Javadoc)
  * @see com.google.gwt.i18n.client.TimeZoneIntf#getGMTString(java.util.DateTime)
  */
 String getGMTString(DateTime date) {
   return _composeGMTString(getOffset(date));
 }

 /* (non-Javadoc)
  * @see com.google.gwt.i18n.client.TimeZoneIntf#getID()
  */
 String getID() {
   return _timezoneID;
 }

 /* (non-Javadoc)
  * @see com.google.gwt.i18n.client.TimeZoneIntf#getISOTimeZoneString(java.util.DateTime)
  */
 String getISOTimeZoneString(DateTime date) {
   int offset = -getOffset(date);
   //
   List<int> data = '+00:00'.codeUnits;
   if (offset < 0) {
     data[0] = '-'.codeUnitAt(0);
     offset = -offset; // suppress the '-' sign for text display.
   }
   data[1] += (offset ~/ 60) ~/ 10;
   data[2] += (offset ~/ 60) % 10;
   data[4] += (offset % 60) ~/ 10;
   data[5] += offset % 10;
   return new String.fromCharCodes(data);
 }

 /* (non-Javadoc)
  * @see com.google.gwt.i18n.client.TimeZoneIntf#getLongName(java.util.DateTime)
  */
 String getLongName(DateTime date) {
   return _tzNames[isDaylightTime(date) ? _DLT_LONG_NAME : _STD_LONG_NAME];
 }

 /* (non-Javadoc)
  * @see com.google.gwt.i18n.client.TimeZoneIntf#getOffset(java.util.DateTime)
  */
 int getOffset(DateTime date) {
   return _standardOffset - getDaylightAdjustment(date);
 }

 /* (non-Javadoc)
  * @see com.google.gwt.i18n.client.TimeZoneIntf#getRFCTimeZoneString(java.util.DateTime)
  */
 String getRFCTimeZoneString(DateTime date) {
   int offset = -getOffset(date);
   //
   List<int> data = '+0000'.codeUnits;
   if (offset < 0) {
     data[0] = '-'.codeUnitAt(0);
     offset = -offset; // suppress the '-' sign for text display.
   }
   data[1] += (offset ~/ 60) ~/ 10;
   data[2] += (offset ~/ 60) % 10;
   data[3] += (offset % 60) ~/ 10;
   data[4] += offset % 10;
   return  new String.fromCharCodes(data);
 }

 /* (non-Javadoc)
  * @see com.google.gwt.i18n.client.TimeZoneIntf#getShortName(java.util.DateTime)
  */
 String getShortName(DateTime date) {
   return _tzNames[isDaylightTime(date) ? _DLT_SHORT_NAME : _STD_SHORT_NAME];
 }

 /* (non-Javadoc)
  * @see com.google.gwt.i18n.client.TimeZoneIntf#getStandardOffset()
  */
 int getStandardOffset() {
   return _standardOffset;
 }

 /* (non-Javadoc)
  * @see com.google.gwt.i18n.client.TimeZoneIntf#isDaylightTime(java.util.DateTime)
  */
 bool isDaylightTime(DateTime date) {
   return getDaylightAdjustment(date) > 0;
 }
}