[tz] Java & Rearguard

Mark Davis ☕️ mark at macchiato.com
Sat Jun 8 14:57:49 UTC 2019

A couple of items.

> CLDR is trying to maintain timezone strings that are suitable for Java
(as almost nobody
else uses them)

We don't know who all uses the timezone names from CLDR (and which flavor);
they are the names used in ICU, which is in C, C++, and Java (with shims
for other programming languages).

However, I agree that CLDR has misleading IDs for the different variants of
a zone name:

generic, standard, daylight.

While these are invisible to users, they can be misleading to programmers.
Names that would have been more reflective of the intended use would have
been something like:

generic, offset0, offset1


On Wed, Jun 5, 2019 at 10:41 PM Paul Eggert <eggert at cs.ucla.edu> wrote:

> On 6/5/19 3:51 AM, Stephen Colebourne wrote:
> > But it has been this way for 20+ years and isn't
> > going to change any time soon. It also produces an answer that as
> > correct as the underlying data (CLDR)
> I'm not sure it's fair to pass this buck to CLDR. CLDR is trying to
> maintain timezone strings that are suitable for Java (as almost nobody
> else uses them) and so if Java is messed up, CLDR will likely be equally
> messed up, to stay compatible with Java.
> Even now (that is, with rearguard format to pacify Java) there are still
> problems with time in Ireland due to Java's confusion on this issue (as
> mimicked by CLDR). See the example at the end of this email, where
> OpenJDK 12 says that local time should be called "GMT" / "Greenwich Mean
> Time" in Ireland on January 1, 1970, which is obviously wrong as Irish
> clocks were one hour ahead of UTC then (and Java gets the UTC offset
> right) and nobody on the ground then would have called that time "GMT".
> That being said, I'm not that pessimistic about whether these problems
> will be fixed. They are obviously fixable; all we need is for Oracle to
> do the fix in OpenJDK, and I'm sure that they can do it if they want to.
> In the meantime the problems do not seem to be that big a deal in practice.
> $ jshell
> |  Welcome to JShell -- Version 12.0.1
> |  For an introduction type: /help intro
> jshell> var epoch = java.time.Instant.EPOCH
> epoch ==> 1970-01-01T00:00:00Z
> jshell> var zone = java.time.ZoneId.of("Europe/Dublin")
> zone ==> Europe/Dublin
> jshell> var dtf =
> java.time.format.DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss Z z
> (zzzz)")
> dtf ==> Value(YearOfEra,4,19,EXCEEDS_PAD)'-'Value(MonthOf ... RT)'
> ''('ZoneText(FULL)')'
> jshell> epoch.atZone(zone).format(dtf)
> $4 ==> "1970-01-01 01:00:00 +0100 GMT (Greenwich Mean Time)"
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