Subtract 6 hours from an existing Date object java (midnight corner case)

Question

I\'ll be using the Calendar api for this. My primary concern is that

            Date birthDate = (...say Apr 20th 0300hrs)
            Calendar ca         


        

Answer 1

No.

After running the following code:

Date birthDate = (...say Apr 20th 0300hrs)
Calendar cal = Calendar.getInstance();
cal.setTime(birthDate);
cal.add(Calendar.HOUR, -6);

you are guaranteed that cal is set to six hours before 'Apr 20th 0300hrs', but not that it is set to 'Apr 19th 2100hrs'.