I need to find the next n Fridays but want to exclude 4th and possibly 5th Fridays, i.e I want to get the next n Fridays which are 1st, 2nd or 3rd of each month. I have found a way to stream over the next n Fridays (example next 10 Fridays):
LocalDate now = LocalDate.now();
Stream.iterate(now , localDate -> localDate.with(TemporalAdjusters.next(DayOfWeek.FRIDAY)))
.skip(1) // skip today
.limit(10)
.forEach(System.out::println);
Output:
2021-10-22 2021-10-29 2021-11-05 2021-11-12 2021-11-19 2021-11-26 2021-12-03 2021-12-10 2021-12-17 2021-12-24
But I need to exclude for example 2021-10-22 & 2021-10-29 because they are 4th and 5th Friday of October. Similarly 2021-11-26 & 2021-12-24 because they are not 1st, 2nd or 3rd Fridays.
I have searched SO and found some ways to calculate nth Friday of a month, for example this one
public static LocalDate nthFridayOfMonth(LocalDate localDate, int week) {
return localDate.with(TemporalAdjusters.dayOfWeekInMonth(week, DayOfWeek.FRIDAY));
}
which returns for a given date the nth Friday.
How to modify this method so that it returns a boolean if a given LocalDate is a first, second or third Friday of a month? Or use this method to implement another method which does what I need?
Ideally I want to use the stream above and use a method, which returns a boolean as a filter:
LocalDate now = LocalDate.now();
Stream.iterate(now , localDate -> localDate.with(TemporalAdjusters.next(DayOfWeek.FRIDAY)))
.skip(1) // skip today
.filter(d -> is1st2ndOr3rdFriday(d))
.limit(10)
.forEach(System.out::println);
to get
2021-11-05 2021-11-12 2021-11-19 2021-12-03 2021-12-10 2021-12-17 2022-01-07 2022-01-14 2022-01-21 2022-02-04
Appreciate any help on how to implement the filter method boolean is1st2ndOr3rdFriday(LocalDate d) {}
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Answer
You can get the ALIGNED_WEEK_OF_MONTH temporal field of the local date, and check if it is ≤ 3.
Stream.iterate(now , localDate -> localDate.with(TemporalAdjusters.next(DayOfWeek.FRIDAY)))
.skip(1) // skip today
.filter(x -> x.get(ChronoField.ALIGNED_WEEK_OF_MONTH) <= 3)
.limit(10)
.forEach(System.out::println);