How to Convert Local Time to GMT in Java?

To convert local time to GMT in Java, we can use the java.util.TimeZone class and its getOffset() method. The getOffset() method returns the offset of a particular time zone from GMT in milliseconds.

Here's an example program that demonstrates how to convert local time to GMT in Java :

Program :

import java.util.Calendar;
import java.util.TimeZone;

public class ConvertLocalToGMT {
    public static void main(String[] args) {
        // Create a calendar object and set the local time
        Calendar calendar = Calendar.getInstance();
        calendar.set(2020, Calendar.APRIL, 22, 14, 30, 0); // Local time: 2:30 PM

        // Get the GMT time zone
        TimeZone gmtTimeZone = TimeZone.getTimeZone("GMT");

        // Get the offset from GMT for the local time zone
        int localOffset = calendar.getTimeZone().getOffset(calendar.getTimeInMillis());

        // Get the offset from GMT for the GMT time zone
        int gmtOffset = gmtTimeZone.getOffset(calendar.getTimeInMillis());

        // Calculate the difference between the local time and GMT time
        int timeDifference = gmtOffset - localOffset;

        // Add the time difference to the local time to get the GMT time
        calendar.add(Calendar.MILLISECOND, timeDifference);

        // Display the GMT time
        System.out.println("GMT Time: " + calendar.getTime());
    }
}

Output :

GMT Time: Wed Apr 22 14:30:00 UTC 2020

In this program, we create a Calendar object and set it to the local time by specifying the year, month, day, hour, minute, and second. Then we get the GMT time zone using the getTimeZone() method of the TimeZone class.

Next, we use the getOffset() method of the TimeZone class to get the offset from GMT for the local time zone and the GMT time zone. We then calculate the time difference between the local time and the GMT time by subtracting the local offset from the GMT offset.

Finally, we add the time difference to the local time using the add() method of the Calendar class, and display the GMT time using the getTime() method of the Calendar class.