date - Determining the next daylight saving day by providing year in java

Question

This question already has answers here: question from:https://stackoverflow.com/questions/65839108/determining-the-next-daylight-saving-day-by-providing-year-in-java

Answer 1

I want to determine the day of the next daylight saving

That is not an answerable question. Daylight savings doesn't work like that. A sensible question would be:

"What is the next day that the clocks change in the current locale" or perhaps "What is the next day that the clocks change in Amsterdam".

There is no one global 'this is the day' across the world.

SimpleDateFormat

This is obsolete old API that you really, really don't want to use to answer this question. The right way to do date stuff in java, is with the java.time package.

ZoneId ams = ZoneId.of("Europe/Amsterdam");
ZoneOffsetTransition trans = ams.getRules().nextTransition(Instant.now());
LocalDateTime date = trans.getDateTimeBefore();
System.out.println(date);

> 2021-03-28T02:00

next time amsterdam switches clocks, it'll be 2 at night, on march 28th, 2021.

Some facts:

• Some zones don't switch at 02:00 at night, but at some other time.
• Some zones will cease switching soon (most of europe, for example).
• When you drive in a single straight line within a single state in the US, you can cross 8 (or possibly more, I can't recall) zones, because (some) reservations do not observe daylight savings but the rest of the state does.
• Countries sometimes announce changes to when they will transition or if they will mere weeks in advance.
• Sometimes, a transition doesn't change 1 hour, it changes 24 hours (such as when a peloponesian island decides they'd rather be on the other side of the international date line).