Display List of TimeZone with GMT and UTC in Java

It is very important to set proper TimeZone in Java code when dealing with Day Light Saving dates. In this section, we will display the list of TimeZone with GMT.

TimeZone

A time zone is an area that observes a uniform standard time for legal, commercial and social purposes. Time zones tend to follow the boundaries between countries and their subdivisions instead of strictly following longitude, because it is convenient for areas in frequent communication to keep the same time. There are the following time zones are available in Java library:

Java timezones for Africa Cities (total 54 time zones are available)

Java timezones for American Cities (total 167 time zones are available)

Java timezones for Antarctica (total 12 time zones are available)

Java timezones for Arctic (total 1 time zones are available)

Java timezones for Asian Cities/Regions (total 99 time zones are available)

Java timezones for Australian Cities/Regions (total 12 time zones are available)

Java timezones for Australian Cities/Regions (total 23 time zones are available)

Java timezones for Brazilian Cities/Region (total 4 time zones are available)

Other regions: Canada, Chile, Cuba, Egypt, Europe, US (total 257 time zones are available)

GMT

GMT stands for Greenwich Mean Time Zone. It is the mean solar time displayed by Shepherd gate clock at the Royal observatory in Greenwich, London counted from midnight. It is used to clearly designate epoch by avoiding confusing reference to local time zone.

When the sun is at its highest point exactly above the Prime Meridian, it is 12:00 noon at Greenwich.

Java Program to Display List of Time zone with GMT

TimeZoneList.java

import java.util.TimeZone;
import java.util.concurrent.TimeUnit;
public class TimeZoneExample
{
  public static void main (String args[])
  {
    String[]ids = TimeZone.getAvailableIDs ();
    for (String id:ids)
      {
	System.out.println (displayTimeZone (TimeZone.getTimeZone (id)));
      }
    System.out.println ("\nTotal TimeZone ID " + ids.length);
  }
  private static String displayTimeZone (TimeZone tz)
  {
    long hours = TimeUnit.MILLISECONDS.toHours (tz.getRawOffset ());
    long minutes = TimeUnit.MILLISECONDS.toMinutes (tz.getRawOffset ())
      - TimeUnit.HOURS.toMinutes (hours);
    // avoid -4:-30 issue
    minutes = Math.abs (minutes);
    String result = "";
    if (hours > 0)
      {
	result =
	  String.format ("(GMT+%d:%02d) %s", hours, minutes, tz.getID ());
      }
    else
      {
	result =
	  String.format ("(GMT%d:%02d) %s", hours, minutes, tz.getID ());
      }
    return result;
  }
}

Output:

Display List of TimeZone with GMT and UTC in Java

The list is too long to show. It displays total 629 time zones with GMT.

Coordinated Universal Time (UTC)

UTC time zone is a standard time zone by which the word regulates clocks and time. It is a constant time scale that does not change for Daylight Saving Time (DST).

UtcExample.java

import java.util.Collections;
import java.util.List;
public class UtcExample 
{
    public static void main(String args[]) 
{
        List timezones7 = DateTimes.fetchTimeZones7(DateTimes.OffsetType.UTC);                
        List timezones8 = DateTimes.fetchTimeZones8(DateTimes.OffsetType.UTC);
        Collections.sort(timezones8);
        timezones8.forEach(System.out::println);
    }    
}

DateTimes.java

import java.time.LocalDateTime;
import java.time.ZoneId;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.Set;
import java.util.TimeZone;
import java.util.concurrent.TimeUnit;
public final class DateTimes 
{
    public enum OffsetType 
{
        GMT, UTC
    }
    private DateTimes() 
{
        throw new AssertionError("Cannot be instantiated");
    }
    public static List<String> fetchTimeZones8(OffsetType type) 
{
        List<String> timezones = new ArrayList<>();
        Set<String> zoneIds = ZoneId.getAvailableZoneIds();
        LocalDateTime now = LocalDateTime.now();
        zoneIds.forEach((zoneId) -> 
{
            timezones.add("(" + type + now.atZone(ZoneId.of(zoneId))
                    .getOffset().getId().replace("Z", "+00:00") + ") " + zoneId);
        });
        return timezones;
    }
    public static List<String> fetchTimeZones7(OffsetType type) 
{
        List<String> timezones = new ArrayList<>();
        String[] zoneIds = TimeZone.getAvailableIDs();
        long timestamp = new Date().getTime();
        for (String zoneId : zoneIds) {
            TimeZone curTimeZone = TimeZone.getTimeZone(zoneId);
            curTimeZone.useDaylightTime();
            String offset = formatOffset(curTimeZone.getOffset(timestamp));
            timezones.add("(" + type + offset + ") " + zoneId);
        }
        return timezones;
    }
    public static String formatOffset(int offset) 
{
        if (offset == 0) 
{
            return "+00:00";
        }
        long offsetInHours = TimeUnit.MILLISECONDS.toHours(offset);
        long offsetInMinutesFromHours = TimeUnit.HOURS.toMinutes(offsetInHours);
        long offsetInMinutes = TimeUnit.MILLISECONDS.toMinutes(offset);
        offsetInMinutes = Math.abs(offsetInMinutesFromHours - offsetInMinutes);
        return String.format("%+03d:%02d", offsetInHours, offsetInMinutes);
    }
}

Output: