<i18n dev> Calendar.set(Calendar.DAY_OF_WEEK, ...) changes times as well

[Naoto Sato]

Hi Lothar,

The behavior is the long standing one: 
https://bugs.openjdk.org/browse/JDK-7055392, and probably not being 
fixed for the compatibility reasons. A workaround would be to issue 
cal.get(Calendar.DAY_OF_WEEK) just after the call to cal.setTimeZone(). 
That will re-calculate fields after the time zone is set.

HTH,
Naoto

On 3/12/24 7:20 AM, Lothar Kimmeringer wrote:
> Hello,
> 
> this might be Dunning Kruger at play (at least my Imposter Syndrom
> tells me it is ;-) but I think I've found a bug in Calendar, when
> working with a different timezonethan the default one.
> 
> Attached you can find my test case that is showing the effect but
> it breaks down to the following:
> 
>          Calendar cal = Calendar.getInstance();
>          cal.setTimeInMillis(1709269200000L); // March 01 2024 06:00:00 CET
>          cal.setTimeZone(TimeZone.getTimeZone(TIMEZONE));
>          assertEquals("Fri Mar 01 06:00:00 CET 2024", 
> cal.getTime().toString(), "check date before change");
>          cal.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
>          assertEquals("Mon Feb 26 06:00:00 CET 2024", 
> cal.getTime().toString(), "check date after change");
> 
> If TIMEZONE is the system's default, the test goes through, if it differs,
> the offset time is added to the resulting date after setting the day of
> the week. With Europe/Berlin (+0100 at that date) as default and
> America/New_York (-0500 at that date) as the timezone being set to the
> Calendar, the result is Mon Feb 26 12:00:00 CET 2024 (previous time plus
> +1 minus -5).
> 
> The workaround for this is using Calendar.add instead of set:
> 
>          cal.add(Calendar.DAY_OF_YEAR, -(cal.get(Calendar.DAY_OF_WEEK) - 
> Calendar.MONDAY));
> 
> sets the day to monday without changes to the time.
> 
> Tested with
> 
>   - Java 8.0.312_win_x64
>   - Java 11.0.20.1_win_x64
>   - Java 17.0.7_win_x64
>   - Java 21.0.0_win_x64
> 
> 
> Thanks and best regards,
> 
> Lothar Kimmeringer