Arne Evertsson Arne Evertsson - 3 days ago 5
Java Question

How to compare two Dates without the time portion?

I would like to have a compareTo method that ignores the time portion of a java.util.Date. I guess there are a number of ways to solve this. What's the simplest way?

Answer

My preference is to use Joda Time which makes this incredibly easy:

DateTime first = ...;
DateTime second = ...;

LocalDate firstDate = first.toLocalDate();
LocalDate secondDate = second.toLocalDate();

return firstDate.compareTo(secondDate);

EDIT: As noted in comments, if you use DateTimeComparator.getDateOnlyInstance() it's even simpler :)

// TODO: consider extracting the comparator to a field.
return DateTimeComparator.getDateOnlyInstance().compare(first, second);

("Use Joda Time" is the basis of almost all SO questions which ask about java.util.Date or java.util.Calendar. It's a thoroughly superior API. If you're doing anything significant with dates/times, you should really use it if you possibly can.)

If you're absolutely forced to use the built in API, you should create an instance of Calendar with the appropriate date and using the appropriate time zone. You could then set each field in each calendar out of hour, minute, second and millisecond to 0, and compare the resulting times. Definitely icky compared with the Joda solution though :)

The time zone part is important: java.util.Date is always based on UTC. In most cases where I've been interested in a date, that's been a date in a specific time zone. That on its own will force you to use Calendar or Joda Time (unless you want to account for the time zone yourself, which I don't recommend.)

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