javalocaldatedate-manipulation

How to get the next n fridays which are the first, second or third friday in a month?


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) {}


Solution

  • 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);