Hi John,
Yes, this is a nice libary. I believe that out of the box it does not
understand leap seconds but I think it would be possible to write a
Chronology that does handle this (as Roland Schweitzer did for AllLeap
and NoLeap calendars).
Cheers, Jon
On Tue, May 27, 2008 at 5:54 PM, John Caron <caron@xxxxxxxxxxxxxxxx> wrote:
> Hi Bob, Steve:
>
> Im impressed by the joda date/time library
> (http://joda-time.sourceforge.net/) and i am likely to start using it. It
> would be useful to see if it deals with this issue, or can easily be extended
> to do so.
>
> Bob Simons wrote:
>>
>> Steve Loch wrote:
>>> I find it surprising, as we are debating issues relating to high-precision
>>> time,
>> that the discussion has not mentioned that UTC is periodically adjusted
>> so as to track
>> mean solar time - so that not all days have 86400 seconds in them. Is
>> care taken in
>> the algorithms to insert the intercalary leap seconds at the appropriate
>> points?
>> TAI and GPS (19 seconds apart) don't use leap seconds according to
>> Wikipedia. There
>> is a (current) proposal to phase out leap seconds in UTC.
>>> Steve Loch
>>
>> I'm not the best person to answer this. But since no one else answered,
>> I'll do my best and hope that others correct me if I'm wrong.
>>
>> The Java documentation is a little vague about leap seconds.
>>
>> The documentation for java.util.Date
>> (http://java.sun.com/j2se/1.5.0/docs/api/java/util/Date.html) indicates
>> the authors were aware of leap seconds, but leave it to the "the host
>> environment" to support them or not. (That seems like the worst
>> solution.) But Date isn't the most relevant class.
>>
>> The documentation for GregorianCalendar
>> (http://java.sun.com/j2se/1.5.0/docs/api/java/util/GregorianCalendar.html),
>> which is the class netcdf-java is probably using for much of the
>> Calendar work, shows no awareness of the leap second issue.
>>
>> I suspect that in almost all installations, Java/GregorianCalendar is
>> unaware of leap seconds. My evidence is that you can take a start
>> date/time, create a GregorianCalendar object, add or subtract any
>> multiple of 86400 seconds (the number of seconds per day), and you get
>> another date with the same time. Comments on different web pages agree.
>>
>> I don't think this makes Java and GregorianCalendar useless for most
>> date/time work. Java still can accurately store a date/time. There is
>> only trouble if you wish to store a date/time that is a leap second or
>> if you want to calculate the elapsed time between two date/times when
>> there is an intervening leap second. If you need to do that, use another
>> library, or augment Java's answer with your own leap second data.
>>
>> And if you really need UTC date/times done right (with leap seconds),
>> you probably have to do it all with your own code. I don't know of a
>> Java high-precision time library (that deals with leap seconds).
>>
>> It isn't an ideal situation.
>>
>> I hope that is helpful.
>>
>> Sincerely,
>>
>> Bob Simons
>> Satellite Data Product Manager
>> Environmental Research Division
>> NOAA Southwest Fisheries Science Center
>> 1352 Lighthouse Ave
>> Pacific Grove, CA 93950-2079
>> (831)658-3205
>> bob.simons@xxxxxxxx
>>
>> The contents of this message are mine personally and
>> do not necessarily reflect any position of the
>> Government or the National Oceanic and Atmospheric
>> Administration.
>> <>< <>< <>< <>< <>< <>< <>< <>< <><
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