Well can't you side step the timezone issue, implement it in the
ReadablePartials
and leave it to the client programmer to convert to timezone savvy
instances,
aware of the issues. Or am I being naive?
If it's about there, I'd sure appreciate it. I seem to want to do this kind
of
thing alot.
--
Mike W
> Hi Mike,
> This looks like something I tried to implement a while back -
> nextMatching(). That is, given a DateTime, find the next DateTime that
> matches the given Partial.
>
> I got this working for dates, but I ran into problems with timezones.
> Timezones were essentially unpredictable, and confused the definition of
> what 'next matching' meant (eg. when DST rules lead to overlapping
> hours). As a result, I stopped work on this concept.
>
> This is some of the code I wrote, and was on the BaseDateTimeField
> class. It was then overridden in subclasses to improve performance.
>
> Basically, if we only implemented this for the Local* classes, then this
> would be easy. Its the timezone thats the hard problem to solve.
>
> Stephen
>
>
>
> //------------------------------------------------------------------------
> /**
> * Finds the next instant that the input instant has the specified
> value.
> * <p>
> * The value of this field will be set into the input milliseconds.
> * The result will always be after the input milliseconds.
> * If the value is invalid, an exception if thrown.
> * <p>
> * Finding the next match avoids changing other fields, especially
> smaller
> * sized ones. For exampe, finding the next 30th dayOfMonth after
> the 31st
> * January will return the 31st March. The time fields will be
> unaltered.
> *
> * @param instant the milliseconds from
> 1970-01-01T00:00:00Z to set in
> * @param value the value to set, in the units of the field
> * @param numberOfRanges the number of ranges to move by, zero has
> no effect
> * @param firstMustChange whether the set must change the date
> * @return the updated milliseconds
> * @throws IllegalArgumentException if the value is invalid
> * @since 1.3
> */
> public long next(long instant, int value, int numberOfRanges,
> boolean firstMustChange) {
> if (numberOfRanges == 0) {
> return instant;
> }
> long millis = set(instant, value);
> if (numberOfRanges > 0) {
> if (millis > instant || (millis == instant &&
> !firstMustChange)) {
> numberOfRanges--;
> }
> if (numberOfRanges > 0) {
> millis = findNext(millis, value, numberOfRanges);
> }
> } else {
> if (millis < instant || (millis == instant &&
> !firstMustChange)) {
> numberOfRanges++;
> }
> if (numberOfRanges < 0) {
> millis = findNext(millis, value, numberOfRanges);
> }
> }
> return millis;
> }
>
> /**
> * Finds the next/previous occurrance of a value.
> *
> * @param millis the milliseconds with a field value equal to value
> * @param value the value to progress to
> * @param numberOfRanges the number of progressions, non-zero
> * @return the updated millis
> * @since 1.3
> */
> protected long findNext(long millis, int value, int numberOfRanges) {
> DurationField range = getRangeDurationField();
> if (range == null || range.isSupported() == false) {
> throw new IllegalFieldValueException(getType(),
> Integer.toString(value));
> }
> int sgn = 1;
> if (numberOfRanges < 0) {
> sgn = -1;
> numberOfRanges = -numberOfRanges;
> }
> // need to handle varying unit/range lengths
> long base = millis;
> for (int j = sgn; numberOfRanges > 0; j += sgn) {
> millis = range.add(base, j);
> if (get(millis) == value) {
> numberOfRanges--;
> }
> }
> return millis;
> }
>
>
>
>
>
> reece wrote:
> > Hi Joda People,
> >
> > Pleases us this API generally does ;-)
> >
> > The bottom line (I think) is - How do I 'roll' a DateTime forward to the
> > next
> > occuring Partial (eg 1st October)?
> >
> > Some other details follow that illustrate the higher problem in
> case there
> > is a better approach...
> >
> > My highish aim is:
> > I have MyPartial of 1st October with just those fields set.
> > I wish to split MyInterval around MyPartial, if of course it
> contains it.
> > I don't see any ambiguity there.
> >
> > 2006-01-01 - 2007-07-01 false
> > 2007-07-01 - 2007-10-02 true
> >
> > There must be a simpler way but at the moment I'm going through this
> > procedure.
> >
> > Sub aim: Convert MyPartial to DateTime of the next year after
> > MyInterval.start
> > So I expected to be able to do some rounding to achieve this - I drew a
> > blank.
> > Instead I can first artificially add 3 months (1,Jan minus 1,Oct) to
> > MyInterval.start and then roundFloor() the year - this gives a
> year I can
> > extract and set on MyPartial, allowing a meaningful MyInstant to be
> > extracted.
> >
> > Using this the following all result in the correct year to set
> on MyPartial
> > in order to give me a date I can split MyInterval around.
> >
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > MyInterval.start: Wed 1 Nov '06
> > plusMonths(3): Thu 1 Feb '07
> > year().roundFloor(): Mon 1 Jan '07
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > MyInterval.start: Thu 1 Feb '07
> > plusMonths(3): Tue 1 May '07
> > year().roundFloor(): Mon 1 Jan '07
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > MyInterval.start: Sun 1 Jul '07
> > plusMonths(3): Mon 1 Oct '07
> > year().roundFloor(): Mon 1 Jan '07
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > MyInterval.start: Sun 30 Sep '07
> > plusMonths(3): Sun 30 Dec '07
> > year().roundFloor(): Mon 1 Jan '07
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > MyInterval.start: Mon 1 Oct '07
> > plusMonths(3): Tue 1 Jan '08
> > year().roundFloor(): Tue 1 Jan '08
> >
> > The problem is, calculating the 3 month period (or whatever period that
> > is depending on MyPartial) since MyPartial may be any point in the year.
> > I see I can do:
> > Days.daysBetween(ReadablePartial start,ReadablePartial end)
> > Which may help but if MyPartial is < 29 Feb then this is going to cause
> > error. In fact I expect that method would fallover without year
> field in the
> > Partial.
> >
> > So the bottom line is - how do I roll a DateTime forward to the next
> > occuring Partial?
> >
> > Thanks,
> > Mike W
> >
> > P.S. Fantastic API - I'll never use that festering JDK library again!!
> >
> >
> >
> >
> >
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