Java: Timezone why different timezone give same value in millisec

Question

I have following code, my target is going to return GMT+0 time in millisec. But Why I always get my local timezone millisec?

Calendar cal = Calendar.getInstance(TimeZone.getTimeZone("GMT"));
Calendar cal2 = Calendar.getInstance();
System.out.println("Time zone id is:"+cal.getTimeZone().getID()+";time in millisec:"+cal.getTimeInMillis());
System.out.println("Time zone id is:"+cal2.getTimeZone().getID()+";time in millisec:"+cal2.getTimeInMillis());

The output is
Time zone id is:GMT;time in millisec:1332740915154
Time zone id is:Europe/Helsinki;time in millisec:1332740915154

Why different Timezone give SAME value in millisec?
I suppose if it is GMT+0 then it should be different value in millisec against local time zone.

Modern comment: I recommend you don’t use `Calendar` and `TimeZone`. Those classes are poorly designed and long outdated. Instead use `Instant` from [java.time, the modern Java date and time API](https://docs.oracle.com/javase/tutorial/datetime/). And `ZoneId` if you need to represent time zones. — Ole V.V., Jul 10 '20 at 16:30

Jon Skeet · Accepted Answer · 2012-03-26T06:27:52.647

24

Why different Timezone give SAME value in millisec?

Because that's what it's meant to do. From the documentation:

(Returns) the current time as UTC milliseconds from the epoch.

In other words, it's the value which would be in the Date returned by getTime - it doesn't depend on the time zone. If you want values which depend on the time zone, use Calendar.Get(Calendar.YEAR) etc.

Both Calendar.getTime() and Calendar.getTimeInMillis() return values representing the instant in time within the calendar, which is independent of both time zone and calendar system.

edited Mar 26 '12 at 06:27

answered Mar 26 '12 at 05:55

Jon Skeet

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My doubt is timezone gives milliseconds or it gives only the requested timezone? – sgowd Mar 26 '12 at 06:00
@sans481: I don't know what you're asking, I'm afraid - could you rephrase the question? – Jon Skeet Mar 26 '12 at 06:01
I am not getting exactly what returns "the current time as UTC milliseconds from the epoch." – sgowd Mar 26 '12 at 06:05
@sans481: It means the number of milliseconds which have elapsed since the Unix epoch of "Midnight January 1st 1970, UTC". – Jon Skeet Mar 26 '12 at 06:12
What about System.currentTimeMillis()? Does it independent of TimeZone? – user84592 Mar 26 '12 at 06:14
It seems it is independ of timezone also. – user84592 Mar 26 '12 at 06:21
@user84592: That's why I said "both time zone and calendar independent". I'll edit it to clarify slightly... – Jon Skeet Mar 26 '12 at 06:27
"If you want values which depend on the time zone, use Calendar.Get(Calendar.YEAR) etc." -- Just what I needed. Thanks – Alkanshel Jul 07 '15 at 17:41

score 6 · Answer 2 · edited Jul 15 '15 at 10:04

6

The millisec of a Date object in Java is just the milliseconds since GMT+0 1970/01/01 00:00:00. It's independent of the Time Zone. Time Zone is a property to format the Date to a readable string.

edited Jul 15 '15 at 10:04

Abdurrahman Mubeen Ali

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answered Mar 26 '12 at 05:54

zsxwing

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That's not really what time zones are for; that's more like what calendars are for. Time zones are to convert between UTC and local time. – Jon Skeet Mar 26 '12 at 06:01

score 1 · Answer 3 · answered Mar 26 '12 at 06:01

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getTimeInMillis() method return the current time as UTC milliseconds from the epoch. So, you are getting same milliseconds even both calendar object has different timezone.

answered Mar 26 '12 at 06:01

kandarp

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Java: Timezone why different timezone give same value in millisec

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