<i18n dev> RFR: 8285844: TimeZone.getTimeZone(ZoneOffset) does not work for all ZoneOffsets and returns GMT unexpected [v2]

[Uwe Schindler]

On Tue, 10 May 2022 17:43:24 GMT, Naoto Sato <naoto at openjdk.org> wrote:

>> src/java.base/share/classes/java/util/TimeZone.java line 543:
>> 
>>> 541:             return new ZoneInfo(totalSecs == 0 ? "UTC" : GMT_ID + tzid, totalSecs);
>>> 542:         } else {
>>> 543:             return getTimeZone(tzid, true);
>> 
>> Before the change in this PR, we used to prefix `GMT` to (non-custom timezone ids) if the timezone id returned by `ZoneId#getId()` started with the `+` or `-` sign, before calling `getTimeZone(modifiedTzid, true)`. 
>> With this change, for `ZoneId`s that aren't `ZoneOffset` instance, we now call `getTimeZone(originalTzid, true)`, without first checking/prefixing the id with `GMT`. Is that an intentional change and would that potentially cause `getTimeZone(String, boolean)` to return a different result?
>
> Yes, it is intentional. The `Time-zone IDs` section in the `ZoneId` class description is clear that zone id starting with "+/-" is a `ZoneOffset` instance. Other ZoneIds should have offsets with prefix or region-based ids.

I was stumbling on this, too, but it is only ZoneOffset isntances that have those strange names without GMT/UTC prefix. Default ZoneId instances created from text strings always have a prefix. If you call ZoneId.of() with an offset only and no prefix it returns a ZoneOffset instance (see the test).

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PR: https://git.openjdk.java.net/jdk/pull/8606