java.util.TimeZone

By / 26 May 2025 / 2 minutes of reading

The java.util.TimeZone class represents a time zone offset and also figures out daylight saving time adjustments. It is used in conjunction with Calendar, Date, and the formatting classes.

Commonly Used Methods

Common Time Zone IDs Examples

  • "UTC"
  • "GMT"
  • "Asia/Kolkata"
  • "America/New_York"
  • "Europe/London"

For More Time Zone ID’s

https://docs.oracle.com/middleware/1221/wcs/tag-ref/MISC/TimeZones.html

Simple Example

import java.util.TimeZone;

public class TimeZoneExample {
    public static void main(String[] args) {
        TimeZone tz = TimeZone.getTimeZone("Asia/Kolkata");
        System.out.println("ID: " + tz.getID());
        System.out.println("Raw Offset (ms): " + tz.getRawOffset());
        System.out.println("Uses DST: " + tz.useDaylightTime());
    }
}

Problem Statement:Listing All TimeZones with GMT Offset

LotusJavaPrince and Mahesh are developing a global banking application. They need to show all supported time zones and their GMT offsets to let users pick their preferred region during account creation.

import java.util.TimeZone;
import java.util.Date;
import java.text.SimpleDateFormat;

public class TimeZoneCaseStudy {
    public static void main(String[] args) {
        String[] zoneIds = TimeZone.getAvailableIDs();
        Date now = new Date();
        SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");

        System.out.printf("%-35s %-10s %-15s\n", "Time Zone ID", "GMT Offset", "Current Time");
        System.out.println("--------------------------------------------------------------");

        for (String id : zoneIds) {
            TimeZone tz = TimeZone.getTimeZone(id);
            int offsetInMillis = tz.getRawOffset();
            int hours = offsetInMillis / (1000 * 60 * 60);
            int minutes = Math.abs((offsetInMillis / (1000 * 60)) % 60);
            String offset = String.format("GMT%+03d:%02d", hours, minutes);

            sdf.setTimeZone(tz);
            String currentTime = sdf.format(now);

            System.out.printf("%-35s %-10s %-15s\n", id, offset, currentTime);
        }
    }
}
Time Zone ID                      GMT Offset Current Time
--------------------------------------------------------------
Asia/Kolkata                      GMT+05:30   21:47:12
America/New_York                 GMT-04:00   12:17:12
Europe/London                    GMT+01:00   17:47:12
...
...

The java.util.TimeZone class is essential for managing regional time settings in applications that support international users. With its powerful methods to manipulate time zone information, it works seamlessly with classes like Calendar, Date, and SimpleDateFormat.

By understanding methods like getTimeZone(), getRawOffset(), and useDaylightTime(), developers can build globally aware applications with accurate time management.

Related Posts

Scroll to Top