Given a Date Object how do I determine the last day of its month?

Question

I'm trying to use the following code but it's returning the wrong day of month.

Calendar cal = Calendar.getInstance();
cal.setTime(sampleDay.getTime());
cal.set(Calendar.MONTH, sampleDay.get(Calendar.MONTH)+1);
cal.set(Calendar.DAY_OF_MONTH, 0);
return cal.getTime();

Answer 1

I would create a date object for the first day of the NEXT month, and then just subtract a single day from the date object.

Answer 2

It looks like you set the calendar to the first day of the next month, so you need one more line to subtract one day, to get the last day of the month that sampleDay is in:

Calendar cal = Calendar.getInstance();
cal.setTime(sampleDay.getTime());
cal.roll(Calendar.MONTH, true);
cal.set(Calendar.DAY_OF_MONTH, 0);
cal.add(Calendar.DAY_OF_MONTH, -1);

In general, it's much easier to do this kind of thing using Joda Time, eg:

DateTime date = new DateTime(sampleDay.getTime());
return date.plusMonths(1).withDayOfMonth(0).minusDays(1).getMillis();

Answer 3

Use calObject.getActualMaximum(calobject.DAY_OF_MONTH)

See Real's Java How-to for more info on this.

Answer 4

I was wrong