在 JSR-310 中查找星期几的下一次出现

Question

Given a JSR-310 object, such as LocalDate , how can I find the date of next Wednesday (or any other day-of-week?

LocalDate today = LocalDate.now();
LocalDate nextWed = ???

Answer 1

The answer depends on your definition of "next Wednesday" ;-)

JSR-310 provides two options using the TemporalAdjusters class.

The first option is next() :

LocalDate input = LocalDate.now();
LocalDate nextWed = input.with(TemporalAdjusters.next(DayOfWeek.WEDNESDAY));

The second option is nextOrSame() :

LocalDate input = LocalDate.now();
LocalDate nextWed = input.with(TemporalAdjusters.nextOrSame(DayOfWeek.WEDNESDAY));

The two differ depending on what day-of-week the input date is.

If the input date is 2014-01-22 (a Wednesday) then:

• next() will return 2014-01-29, one week later
• nextOrSame() will return 2014-01-22, the same as the input

If the input date is 2014-01-20 (a Monday) then:

• next() will return 2014-01-22
• nextOrSame() will return 2014-01-22

ie. next() always returns a later date, whereas nextOrSame() will return the input date if it matches.

Note that both options look much better with static imports:

LocalDate nextWed1 = input.with(next(WEDNESDAY));
LocalDate nextWed2 = input.with(nextOrSame(WEDNESDAY));

TemporalAdjusters also includes matching previous() and previousOrSame() methods.