LocalDate from YearMonth with nth DayOfWeek

user_9146732 0
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I would like to convert a YearMonth to a LocalDate with the specified DayOfWeek, e.g. the second Tuesday of February 2019.

The following code throws a DateTimeException:

YearMonth yearMonth = YearMonth.of(2019, Month.FEBRUARY);
TemporalAdjuster secondTuesday = TemporalAdjusters.dayOfWeekInMonth(2, DayOfWeek.TUESDAY);

LocalDate date = LocalDate.from(yearMonth).with(secondTuesday);

In order to make my code work I need to replace the last line with

LocalDate date = yearMonth.atDay(1).with(secondTuesday);

Isn't there a cleaner solution that doesn't require the use of atDay(1)?

localdate java-8 time java
2 Answers

You have found the best and cleanest (or the least poor) solution yourself already:

LocalDate date = yearMonth.atDay(1).with(secondTuesday);

The argument to atDay doesn’t necessarily need to be 1, but it needs to be a valid day of the month in question, so why not 1?

with() always returns the same type you called it on. That is, YearMonth.with() will always return a YearMonth, never a LocalDate. Therefore you cannot use your adjuster there.

I understand and share your objection, but what you’ve got already is the best we can do. You can and should probably wrap it inside a method with a nice name.

user_57728820

I believe that your code is almost done. The important point is for use the TemporalAdjusters.dayOfWeekInMonth() method you need to provide a LocalDate with day.

Your example is right, but if you want to be little bit more clear, you can change for:

TemporalAdjuster secondTuesday = TemporalAdjusters.dayOfWeekInMonth(2, DayOfWeek.TUESDAY);
LocalDate dateLocalDate = LocalDate.of(2019, Month.FEBRUARY, 1).with(secondTuesday);

And put this code into a method, like this:

public static void main(String[] args) {
    LocalDate localDate = getLocalDateByDayOfWeek(2019, Month.FEBRUARY, 2, DayOfWeek.TUESDAY);
    System.out.println(localDate);
}

private static LocalDate getLocalDateByDayOfWeek(int year, Month month, int weekNumber, DayOfWeek dayOfWeek) {
    TemporalAdjuster temporalWeek = TemporalAdjusters.dayOfWeekInMonth(weekNumber, dayOfWeek);
    return LocalDate.of(year, month, 1).with(temporalWeek);
}

Here you can find the documentation about this method: TemporalAdjusters Docs

user_100616270
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