datetime - How to round time to the nearest quarter hour in java?

Question

Given today's time e.g. 2:24PM, how do I get it to round to 2:30PM?

Similarly if the time was 2:17PM, how do I get it to round to 2:15PM?

Answer 1

Rounding

You will need to use modulo to truncate the quarter hour:

Date whateverDateYouWant = new Date();
Calendar calendar = Calendar.getInstance();
calendar.setTime(whateverDateYouWant);

int unroundedMinutes = calendar.get(Calendar.MINUTE);
int mod = unroundedMinutes % 15;
calendar.add(Calendar.MINUTE, mod < 8 ? -mod : (15-mod));

As pointed out by EJP, this is also OK (replacement for the last line, only valid if the calendar is lenient):

calendar.set(Calendar.MINUTE, unroundedMinutes + mod);

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Improvements

If you want to be exact, you will also have to truncate the smaller fields:

calendar.set(Calendar.SECOND, 0);
calendar.set(Calendar.MILLISECOND, 0);

You can also use DateUtils.truncate() from Apache Commons / Lang to do this:

calendar = DateUtils.truncate(calendar, Calendar.MINUTE);