The problem here is: It is not possible to transform a date object to
another time zone because internally the date object always uses UTC. I
don't want to transform the date object itself because then it would refer
to a different point in time. Look at the getTime method of the Date object:
getTime returns the number of milliseconds between the desired point in time
and midnight on January 1, 1970 (UTC). If you transform that date object the
number of milliseconds changes so it would *not* refer to the same point in
time anymore which means that date is false.
A certain date object denotes one point in time which can be expressed in
different ways. Example: The date 2010/12/14 9:00 UTC refers to the same
point in time as 2010/12/14 11:00 UTC+2 (or CEST). So if I want to display
that date in a certain format I should tell the *formatter* which
representation of that one date object to use.
In my case I'd like to format a date object like "dd.MM.yyy HH:mm" and
display it in UTC. My date object is 2010/12/14 9:00 UTC. My time zone here
in Germany is UTC+1 in winter. Then the DateFormat class formats the date
like this: "14.12.2010 10:00". However, I want the date to be displayed in
UTC so according to your advice I would have to change my date object to
2010/12/14 8:00 UTC to get the desired result from the DateFormat class.
This seems to work at first sight, but it does not: Look at the dates Mar 28
2010 00:59 UTC and Mar 28 2010 01:00 UTC. This is the point in time when CET
changes to CEST. The DateFormat class formats the first date "28.03.2010
01:59" but the second "28.03.2010 03:00". It is not possible to get, for
example, the string "28.03.2010 02:00" from the DateFormat class although
this date exists in UTC.
You see, date transformation doesn't work here. It's an issue of different
representations of one moment in time.
2010/12/14 thron7 <[email protected]>
> Well, as I wrote, my understanding is that what you call UTC, is actually
> UTC-0 which is, like it or not, a time zone (London time). Adding a UTC-0
> API to some framework class would be of limited usability. More
> interesting in my eyes would be an API that allows transformation of a
> date object to *any* time zone, but YMMV.
>
> T.
>
> >> On 12/13/2010 05:36 PM, Marius Austerschulte wrote:
> >> > Hi Alex,
> >> > I know that the DateFormat class is for formatting a date. I just
> >> > wondered why only the local representation of the date can be
> >> formatted,
> >> > not the UTC representation.
> >>
> >> I find what you write confusing. Any time, including the local, can be
> >> represented in UTC. Date.getUTCDate and friends provide the current time
> >> for a *specific* time zone, namely UTC-0. Is it this you're referring
> >> to? Then what you want is a date expressed in this particular time zone.
> >>
> >
> > I want that date being expressed in its UTC representation. A time zone
> is
> > an area on the earth's surface which has a uniform time. This time is
> > computed using an offset from UTC. The offset for a time zone may differ
> > during the year (e.g. the offset for the time zone of London in winter is
> > 0,
> > but +1 in summer). So I don't want the time of a certain time zone but
> the
> > universal time, which is UTC.
> >
> >
> >> > It would be nice if you could get a
> >> > formatted UTC representation of the date by using a format string like
> >> > "dd.MM.yyyy" instead of having to build a date string manually like
> >> > d.getUTCDate() + "." + d.getUTCMonth() + ...
> >>
> >> But that would require date calculation, which, as Alex suggested, the
> >> DateFormat class is not about. That would require a completely different
> >> class.
> >>
> >
> > Why does it require date calculation? The JavaScript API already provides
> > the methods to get the correct date in UTC, so there wouldn't be the need
> > for any further date calculation by the DateFormat class. I just want the
> > DateFormat.format method (or maybe a potential DateFormat.formatUTC
> > method)
> > to format that UTC time according to a certain format-string. So from my
> > point of view I can't see a big problem with enhancing the DateFormat
> > class
> > with such a feature.
> >
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