Comparing two java.util.Dates to see if they are in the same day

How about:

SimpleDateFormat fmt = new SimpleDateFormat("yyyyMMdd");
return fmt.format(date1).equals(fmt.format(date2));

You can also set the timezone to the SimpleDateFormat, if needed.

Calendar cal1 = Calendar.getInstance();
Calendar cal2 = Calendar.getInstance();
cal1.setTime(date1);
cal2.setTime(date2);
boolean sameDay = cal1.get(Calendar.DAY_OF_YEAR) == cal2.get(Calendar.DAY_OF_YEAR) &&
                  cal1.get(Calendar.YEAR) == cal2.get(Calendar.YEAR);

Note that "same day" is not as simple a concept as it sounds when different time zones can be involved. The code above will for both dates compute the day relative to the time zone used by the computer it is running on. If this is not what you need, you have to pass the relevant time zone(s) to the Calendar.getInstance() calls, after you have decided what exactly you mean with "the same day".

And yes, Joda Time's LocalDate would make the whole thing much cleaner and easier (though the same difficulties involving time zones would be present).

I use the "apache commons lang" package to do this (namely org.apache.commons.lang.time.DateUtils)

boolean samedate = DateUtils.isSameDay(date1, date2);  //Takes either Calendar or Date objects