<i18n dev> Incorrect TimeZone display name when DST not applicable / disabled

[Deven You]

Hi All,

JDK displays incorrect TimeZone display name when DST (Daylight Saving 
Time) is disable in the native Time Zone settings on Windows XP/2003 
platforms and the Time Zone does not support DST.

Steps to re-create the problem

1. In the Windows Date and Time Properties dialog, set the time zone to 
one that uses DST (e.g. Greenwich Mean Time).
2. Disable the 'Automatically adjust clock for Daylight Saving Changes' 
option.
3. Change the time zone to one that does not use DST (e.g. India 
Standard Time - (GMT+5:30) Chennai,Kolkata,Mumbai,New Delhi)
4. Compile and run the testcase[1]

Observed output:
GMT+05:30

Expected output:
India Standard Tim

There is already a sunbug[2] for this problem, which describes the 
problem clearly and very detailed. Please refer it for more detail.
Here is some descriptions from the sunbug:

PROBLEM
---------------------------------
Windows provides an option entitled 'Automatically adjust clock for 
Daylight Saving Changes' box in the native time zone settings. When 
checked, the clock is automatically adjusted to the daylight savings 
time if applicable to that particular timezone.
More importantly, if this box is unchecked, Windows will ignore any DST 
timetable in the selected time zone.

Now, the JDK's TimeZone class checks the value of the registry value 
that corresponds to this option, and modifies the default TimeZone's 
display name accordingly. This is from the evaluation of CR 4296930, 
describing the fix made for that CR in JDK 1.4.2:

--------
When the auto-adjustment is turned off, the platform time zone detection 
code will create a time zone ID in the "GMT{+|-}hh:mm" form with which a 
custom TimeZone customer is created. This is because some Windows users 
turn it off due to incorrect Win32 time zones and choose one based on 
just the GMT offset. A restriction is that display names are not 
supported even it just means to use standard time of a correct time zone 
selection for some other purposes.
--------

This makes sense for time zones that do use DST. However, our customers 
have found that if you disable DST in the Windows options for a time 
zone that uses it, and then switch to a time zone that doesn't use DST, 
the option remains disabled (i.e. the underlying registry value retains 
the value that corresponds to the option being disabled).

Under these circumstances the JDK's TimeZone class changes the display 
name to the "GMT{+|-}hh:mm" format, rather than using the correct name. 
This is unintuitive, and arguably incorrect.

We believe it would be better to query the time zone to see if DST is 
actually applicable before deciding whether or not to switch to the 
"GMT{+|-}hh:mm" format.

Note that this issue is not applicable to Windows Vista/7 because the 
relevant registry value is reset each time the native time zone is 
changed, rather than being retained as it is in Windows XP/2003.




I have made a fix which will deal with this situation and avoid the 
"GMT{+|-}hh:mm" format.

[1] http://cr.openjdk.java.net/~littlee/ojdk-557/webrev.00/ 
<http://cr.openjdk.java.net/%7Elittlee/ojdk-557/webrev.00/>
[2] http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7094176

Thanks a lot!

-- 
Best Regards,

Deven

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