Thanks very much Stephen.
Would it be worth mentioning the similarities between long milliseconds and
Unix
time in the documentation?
If the two are in fact the same (unfortunately, apart from Brian's reply and a
couple of web pages, I've been unable to find any "official" confirmation of
this), it seems one might save a lot of effort by simply pointing people to the
Unix time definition.
Winston
________________________________
From: Stephen Colebourne <[email protected]>
To: Discussion of the Joda project <[email protected]>
Sent: Tue, 13 July, 2010 12:13:48
Subject: Re: [Joda-interest] A few questions for the experts
Brian has made the key points. I'd add that choosing a definition of
long milliseconds that exactly matched the JDK was important in
getting Joda-Time widely adopted.
That the JDK chooses to ignore leap seconds (as UNIX did) is one that
annoys many time "experts" but doesn't impact most users - people
don't tend to care much about leap seconds. JSR-310 will allow people
to care if they want to. It also properly defines the meaning of
1970-01-01 when leap-second UTC doesn't start until 1972.
Stephen
On 12 July 2010 15:24, Brian S O'Neill <[email protected]> wrote:
> 1. The Java and Joda-time epoch are the same -- Unix time with
> millisecond precision.
>
> 2. Lack of leap seconds simply means that if you wanted to know the
> number of seconds elapsed between now and some datetime in the past, it
> would be off a little bit. Joda-time assumes that the length of a day
> (ignoring timezones) is always 86400 seconds.
>
> 3. Parsing a datetime string would be ambiguous only if the leap second
> was included in it. Ordinarily, the seconds field is only 0..59, but a
> leap second (or two) allows 0..61.
>
> 4. Publishing the epoch makes it much easier to convert to different
> formats and perform calculations. Otherwise, the only approach would be
> to extract calendar type, time zone, era, year, month, day, hour,
> minute, second, millis always. Converting between calendar systems is an
> amazing challenge if these are the only exposed values.
>
> You should probably read the jsr 310 threads. All of these questions
> come up again and again.
>
> https://jsr-310.dev.java.net/servlets/SummarizeList?listName=dev
>
>
> On 2010-07-12 03:11 AM, Winston Gutkowski wrote:
>> Dear Joda experts,
>>
>>
>> I've been contributing to a long, but ultimately rather fruitless, thread on
>>the
>> Sun Java forums about the java.util.Date class, and was hoping that one of
>your
>> experts might be able to answer a few questions for me:
>>
>> 1. The published epoch for the Date class is given as 1/1/1970 00:00:00 GMT
(I
>> notice Joda's DateTime epoch specifies Zulu time, which I assume amounts to
>the
>> same thing). When exactly is this in terms of UTC, which was not standardized
>> until 1972? Or do they both in fact use "1/1/1970 00:00:00 UTC proleptic", as
>> Unix time does?
>>
>> 2. The Joda FAQ states that Joda time does not support leap seconds. Does
this
>> mean that Joda's 'ticker' (and therefore presumably Java's) adjusts for this
>in
>> some way, like Unix's; or simply that leap seconds are ignored for the
>>purposes
>> of displaying human-readable timestamps?
>>
>>
>> 3. If the answer to Q2 is "the latter", what are the rules for parsing a date
>> string that might be ambiguous?
>>
>> 4. What was Joda's rationale for publishing its DateTime epoch? I've been
>> arguing that there was no good reason for Java's Date class to do so, since
it
>>
>> (a) Anchors the date from an instant that people believe they "understand".
>> (b) Encourages buggy conversion methods written in the mistaken belief that
>>it's
>> "simple".
>> (c) Prevents the epoch from being changed in the event of a new time
standard,
>> or simply to make internal calculations more efficient.
>>
>> Thanks in advance for any answers.
>>
>> Winston Gutkowski
>>
>
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