Issue with GregorianCalendar class

Question

Hi I'm having issues with the GregorianCalender class. I am trying to enable daylight savings time but it doesn't seem to be working properly for. As a test I have taken the difference of time (in milliseconds) between a date where daylight savings causes a shift in time (April 4, 2004 for example). The two sample dates I have chosen are April 5, 2004 and April 4, 2004, ideally the time difference should be 23 hrs (since one hour is lost due to daylight savings) but I am getting 24hrs. I have a sample program in C++ which gives me the correct answer so I know the result am I getting here is wrong. Anybody have any suggestions?
String[] ids = TimeZone.getAvailableIDs(-8 * 60 * 60 * 1000);
     if (ids.length == 0)
     System.exit(0);
     // create a Pacific Standard Time time zone
     SimpleTimeZone pdt = new SimpleTimeZone(-8 * 60 * 60 * 1000, ids[0]);
     // set up rules for daylight savings time
     pdt.setStartRule(Calendar.APRIL, 1, Calendar.SUNDAY, 60 * 60 * 1000, true);
     pdt.setEndRule(Calendar.OCTOBER, 31, Calendar.SUNDAY, 60 * 60 * 1000, false);
     pdt.setDSTSavings( 60*60*1000 );
     GregorianCalendar cal = new GregorianCalendar(2004, 4, 4);
     GregorianCalendar cal1 = new GregorianCalendar(2007, 4, 5);
     cal1.setTimeZone ( pdt );
     cal.setTimeZone( pdt );
//This values is incorrect
     long diff = cal1.getTimeInMillis() - cal.getTimeInMillis();     
//I have also tried the following
String[] ids = TimeZone.getAvailableIDs(-8 * 60 * 60 * 1000);
     if (ids.length == 0)
     System.exit(0);
     // create a Pacific Standard Time time zone
     SimpleTimeZone pdt = new SimpleTimeZone(-8 * 60 * 60 * 1000, ids[0]);
     // set up rules for daylight savings time
     pdt.setStartRule(Calendar.APRIL, 1, Calendar.SUNDAY, 60 * 60 * 1000, true);
     pdt.setEndRule(Calendar.OCTOBER, 31, Calendar.SUNDAY, 60 * 60 * 1000, false);
     pdt.setDSTSavings( 60*60*1000 );
     GregorianCalendar cal = new GregorianCalendar(pdt);
     GregorianCalendar cal1 = new GregorianCalendar(pdt);
     cal1.set(2004, 4, 5 );
     cal.set( 2004, 4, 4 );
//This values is incorrect
     long diff = cal1.getTimeInMillis() - cal.getTimeInMillis();     
Thanks

Answer 1

There may be any of several issues:
Daylight savings time moves from year to year. Maybe last year, it was not on the same week number.
Daylight savings time officially occurs at 2am. Java date's default to midnight if explicitly initialized. So, try calculating from after 2-3 am, depending on which way time was shifted.- Saish
"My karma ran over your dogma." - Anon