Java: How do I get the date of x day in a month ( e.g. Third Monday in February 2012)

Question

I am somewhat struggling with this.

I want to setup my Calendar to let's say: Third Monday in February 2012. And I didn't find any way of doing this using Java.

For example, if I wanted to set my calendar for Christmas 2011, I can do this easily, this way:

Calendar when = Calendar.getInstance();
when.set (Calendar.MONTH, Calendar.DECEMBER);
when.set (Calendar.DAY_OF_MONTH, 25)
when.set (Calendar.YEAR, 2011);

But I am lost as to how to set it up for let's say Memorial Day 2012, which is the last Monday of May. This is my code, but it's obviously wrong, because I simply can't assume that the last Monday of May will be in the 4th week of May that year:

Calendar when = Calendar.getInstance ();
when.set (Calendar.DAY_OF_WEEK,Calendar.MONDAY);
when.set (Calendar.MONTH, Calendar.MAY);
when.set (Calendar.WEEK_OF_MONTH, 4)
when.set (Calendar.YEAR, 2012);

Any suggestions as to how I can programatically find out, in which week of the month of May 2012 (in example above) is the last Monday? Assuming I can get that information, I should be able to get my code above to work.

I need something which would basically work for any other examples. Something which could give an exact day for the same scenarios. Examples:

Which date is:

• 3rd Thursday of May 2015
• 1st Monday of June 2050
• 4th Tuesday of December 2012
• 2nd Wednesday of July 2000

I really need this for my project and I am sure it's simple, but I am breaking my head on this without any real results to show for :) And also couldn't find anything on the net.

---

Added:

Ok, this is where I've got for the last Monday in a month:

when.set (GregorianCalendar.MONTH, GregorianCalendar.MAY);
when.set (GregorianCalendar.DAY_OF_WEEK, Calendar.MONDAY);
when.set (GregorianCalendar.DAY_OF_WEEK_IN_MONTH, -1);
when.set (Calendar.YEAR, 2012);

But I am not sure how would I go about doing for example seconds Monday in the same month, like this?

when.set (GregorianCalendar.DAY_OF_WEEK_IN_MONTH, 2);

Any suggestions?

Answer 1

To do date arithmetic in Java (and in general, to do anything with datetimes, except for the most trivial things) Joda-Time is the answer:

public static LocalDate getNDayOfMonth(int dayweek,int nthweek,int month,int year)  {
   LocalDate d = new LocalDate(year, month, 1).withDayOfWeek(dayweek);
   if(d.getMonthOfYear() != month) d = d.plusWeeks(1);
   return d.plusWeeks(nthweek-1);
}

public static LocalDate getLastWeekdayOfMonth(int dayweek,int month,int year) {
   LocalDate d = new LocalDate(year, month, 1).plusMonths(1).withDayOfWeek(dayweek);
   if(d.getMonthOfYear() != month) d = d.minusWeeks(1);
  return d;
}

public static void main(String[] args) {
   // second wednesday of oct-2011
   LocalDate d = getNDayOfMonth( DateTimeConstants.WEDNESDAY, 2, 10, 2011);
   System.out.println(d);
   // last wednesday of oct-2011
   LocalDate dlast = getLastWeekdayOfMonth( DateTimeConstants.WEDNESDAY,  10, 2011);
   System.out.println(dlast);
}

---

Edit: Since Java 8 (2014) the new Date API (package java.time), which is inspired by/similar to Jodatime, should be preferred.