Comments on: Date puzzle

By: Antony Stubbs

Antony Stubbs — Sat, 21 Feb 2009 05:07:03 +0000

Seriously. two words:
Joda Time

http://joda-time.sourceforge.net/

By: Birkof

Birkof — Tue, 02 Dec 2008 16:00:36 +0000

Output of your code on my PC is following:
Thu Jan 01 00:00:00 GMT 1970
0

So it will not print -3600000 everywhere on the planet, as you wrote. Used Java 1.5.0_04.

Yes, it depends on Timezone. But that's correct, not surprising behaviour. It is because you are asking what is different between already set timezone and GMT timezone.

For example, when you add these lines:
TimeZone tz = TimeZone.getTimeZone("GMT+0:00");
calendar.setTimeZone(tz);

the result must be on every PC 0.

When you add different number, then it depends on the difference between particular timezone and GMT.

Anyway, these "Calendar+Timezone" classes/API is so complicated. It is because there are influed by historical and political reasons. So they are very different from the rest of any APIs, where logic works.

By: Lukáš Křečan

Lukáš Křečan — Thu, 27 Nov 2008 19:15:07 +0000

Indeed, the one hour difference points to timezones, daylight savings or something similar. It is tempting to rule out the daylight saving, January is usually in the winter and daylight savings are applied in the summer. The correct answer is quite surprising. The GMT from JavaDoc is not the same as the GMT used in Date, Calendar and TimeZone. The GMT from JavaDoc refers to standard time (UTC). The GMT from Date class refers to London time (British Standard Time). And as you certainly know, between years 1968 and 1972 those crazy Brits kept summer time even over the winter. Thanks to them, we have quite confusing behaviour in our Java classes. Lets hope it will get better with the new DateTime Java library. For more information you can read following bug report and nice article about British time.

By: Lasica

Lasica — Thu, 27 Nov 2008 17:12:42 +0000

Just guess: Daylight saving time offset?

By: Lukáš Křečan

Lukáš Křečan — Thu, 27 Nov 2008 09:02:38 +0000

Yes, -3600000 is printed. But it is printed even here in Dublin and I hope that we would get the same result everywhere on the planet. So I am afraid it has nothing to do with Czech Republic.

By: PB

PB — Wed, 26 Nov 2008 23:08:42 +0000

Calendar and Date are timezone-senzitive, aren't they? So key is in "GMT" If ran in Czech Republic, value of 3600000 will be printed ... at least I think.