Question

Consider the following code to only determine if the time component of one Date object is before the time component of another Date object:

private boolean validStartStopTime( Date start, Date stop ) {
  Calendar startCal = Calendar.getInstance();
  Calendar stopCal = Calendar.getInstance();

  startCal.clear();
  stopCal.clear();

  startCal.setTime( start );
  stopCal.setTime( stop );

  startCal.set( Calendar.YEAR, 2011 );
  stopCal.set( Calendar.YEAR, 2011 );
  startCal.set( Calendar.MONTH, 1 );
  stopCal.set( Calendar.MONTH, 1 );
  startCal.set( Calendar.DAY_OF_YEAR, 1 );
  stopCal.set( Calendar.DAY_OF_YEAR, 1 );

  return startCal.before( stopCal );
}

Would this insure that time comparison is correct? Is there a better alternative (Joda is not an option)? I believe that this is equivalent to setting the Calendar objects to current date/time and manually copying over the hour, minutes, and milliseconds component. You can assume that timezone are the same.

EDIT: To clarify what I mean by comparing only the time component of a Date object. I mean that when looking specifically at the time portion, the start time is before the stop time. The date portion is ABSOLUTELY irrelevant (in that start=”Jan 2 20011 10AM” and end=”Jan 1 2011 11AM” is perfectly fine), if I had a choice I’d simply use something that contained just the time but a Date object is what I’m given. I’d like to not write a sequence of if-else which is why I have the approach above but I welcome a cleaner/better approach.

Answer 1

Your code should work fine. You could also format just the time components in a zero-based string notation and compare them lexicographically:

public static boolean timeIsBefore(Date d1, Date d2) {
  DateFormat f = new SimpleDateFormat("HH:mm:ss.SSS");
  return f.format(d1).compareTo(f.format(d2)) < 0;
}

[Edit]

This is assuming that the dates have the same timezone offset. If not you’ll have to adjust them manually beforehand (or as part of this function).