Confusion with Java Calendar and time zones

Question

Consider the following code fragment...

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


public class Main {
    public static void main(String[] args) {

        Calendar c = Calendar.getInstance();
        System.out.println(c.getTimeZone().getDisplayName());
        System.out.println(c.getTime());
        System.out.println(c.get(Calendar.HOUR_OF_DAY));

        Calendar gmtCal = Calendar.getInstance(TimeZone.getTimeZone("GMT"));
        System.out.println(gmtCal.getTimeZone().getDisplayName());
        System.out.println(gmtCal.getTime());
        System.out.println(gmtCal.get(Calendar.HOUR_OF_DAY));

        Calendar c2 = Calendar.getInstance(TimeZone.getTimeZone("US/Alaska"));
        System.out.println(c2.getTimeZone().getDisplayName());
        System.out.println(c2.getTime());
        System.out.println(c2.get(Calendar.HOUR_OF_DAY));
    }
}

The output of this program is

Eastern Standard Time
Mon Jul 13 16:10:14 EDT 2015 
16
Greenwich Mean Time
Mon Jul 13 16:10:14 EDT 2015  //<--- also not sure why this isn't 4 hours ahead as Eastern time is UTC/GMT - 4 right now due to DST
20
Alaska Standard Time
Mon Jul 13 16:10:14 EDT 2015 //<--- date is not reflecting correct time and is showing EDT versus AST
12

Why does the get(Calendar.HOUR_OF_DAY) method call not match the hour in the getTime() method call? Another way to put it, is why isn't this the output?

Eastern Standard Time
Mon Jul 13 16:10:14 EDT 2015
16
Greenwich Mean Time
Mon Jul 13 20:10:14 GMT 2015
20
Alaska Standard Time
Mon Jul 13 12:10:14 AST 2015
12

Edit... So how can I get the following

long t = 1436842840327L;
Calendar c = Calendar.getInstance();
c.setTimeInMillis(t);
c.setTimeZone(TimeZone.getTimeZone("US/Alaska"));
System.out.println(c.getTime());
System.out.println(c.get(Calendar.HOUR_OF_DAY) + ":" + c.get(Calendar.MINUTE) + ":" + c.get(Calendar.MILLISECOND));

to print the same hour as in getTime()? The output currently is

Mon Jul 13 23:00:40 EDT 2015
19:0:327

If you use `Java 8` you may want to work with [`LocalDateTime`](https://docs.oracle.com/javase/8/docs/api/java/time/LocalDateTime.html) instead. — PM 77-1, Jul 13 '15 at 20:46

Maximillian Laumeister · Accepted Answer · 2015-07-13T20:48:18.053

4

The function getTime() returns a Date object, and Date objects, when when converted to a string, are represented using your default time zone.

So by using getTime() you're getting a Date object that no longer contains the timezone data (a Date is just a specific point in time). Then that Date object gets implicitly converted to a string when it's printed.

edited Jul 13 '15 at 20:48

answered Jul 13 '15 at 20:45

Maximillian Laumeister

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@TryCatch You mean how to get it to work how you'd expect? I would look into using the SimpleDateFormat class, here's a related question: https://stackoverflow.com/questions/18122608/simpledateformat-parse-loses-timezone – Maximillian Laumeister Jul 13 '15 at 21:34

score 2 · Answer 2 · edited Jul 13 '15 at 21:04

2

Java doc clearly states for method getInstance():

public static Calendar getInstance()
Gets a calendar using the default time zone and locale. The Calendar returned is based on the current time in the default time zone with the default locale.

(emphasis mine)

edited Jul 13 '15 at 21:04

Tom

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answered Jul 13 '15 at 20:46

Rahul Prasad

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Confusion with Java Calendar and time zones

2 Answers2

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