FULL PRODUCT VERSION :
java version "1.5.0_07"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_07-b03)
Java HotSpot(TM) Client VM (build 1.5.0_07-b03, mixed mode, sharing)


ADDITIONAL OS VERSION INFORMATION :
WIndows XP Pro Service Pack 2

A DESCRIPTION OF THE PROBLEM :
setting HOUR_OF_DAY to zero using Calendar's set(Calendar.HOUR_OF_DAY,0) method only works as expected for a calendar using default TimeZone.

For other non-default TimeZones, the hour field is NOT set to zero; rather it is set to a number predictably dependent on the TimeZone being used.



STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
see included source code - nothing fancy


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
expected hour to be set to zero regardless of calendar's timezone

ACTUAL -
Demonstrate set Calendar HOUR_OF_DAY bug:
   Expected: HOUR_OF_DAY = 0
   Results: HOUR_OF_DAY = non-zero (predictably dependent on Calendar's TimeZone)
Calendar.TimeZone(Default)=GMT-05:00
Calendar.TimeZone(CST) =GMT-06:00
Calendar.TimeZone(PST) =GMT-08:00
Date=01/02/03 04:05:06 [original date as a String]
Date=01/02/03 04:05:06 [Date parsed from string]
Date=01/02/03 04:05:06 [Calendar-Default]
Date=01/02/03 04:05:06 [Calendar-CST]
Date=01/02/03 04:05:06 [Calendar-PST]
Now set HOUR_OF_DAY to zero using cal.set(Calendar.HOUR_OF_DAY,0):
Date=01/02/03 00:05:06 [Calendar-Default][Hour=0]
Date=01/02/03 01:05:06 [Calendar-CST ][Hour=0] <---BUG?
Date=01/02/03 03:05:06 [Calendar-PST ][Hour=0] <---BUG?
----- HOUR_OF_DAY not as expected -----


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
/*
 * CalendarSetBug.java
 *
 * Created on July 20, 2006, 10:00 AM
 *
 */

package calendarbug;
import java.util.*;
import java.text.*;

/**
 *
 * Demonstrate bug in java.util.Calendar
 * Setting HOUR_OF_DAY to zero yields non-zero results
 * for non-default TimeZones.
 *
 */
public class CalendarSetBug {
    Calendar cal; // calendar default timezone
    Calendar calCST; // calendar CST timezone
    Calendar calPST; // calendar PST timezone
    String sdt; // initial datetime string
    Date dt; // datetime
    DateFormat df = new SimpleDateFormat("MM/dd/yy HH:mm:ss");
    
    public CalendarSetBug() {
        System.out.printf("Demonstrate set Calendar HOUR_OF_DAY bug:\r\n");
        System.out.printf(" Expected: HOUR_OF_DAY = 0\r\n");
        System.out.printf(" Results: HOUR_OF_DAY = non-zero (predictably dependent on Calendar's TimeZone)\r\n");

        cal = Calendar.getInstance(TimeZone.getDefault());
        calCST = Calendar.getInstance(TimeZone.getTimeZone("GMT-06:00"));
        calPST = Calendar.getInstance(TimeZone.getTimeZone("GMT-08:00"));

        System.out.printf("Calendar.TimeZone(Default)=%s\r\n",cal.getTimeZone().getDisplayName());
        System.out.printf("Calendar.TimeZone(CST) =%s\r\n",calCST.getTimeZone().getDisplayName());
        System.out.printf("Calendar.TimeZone(PST) =%s\r\n",calPST.getTimeZone().getDisplayName());

        try {
            sdt="01/02/03 04:05:06";
            dt = df.parse(sdt);
            cal.setTime(dt);
            calCST.setTime(dt);
            calPST.setTime(dt);

            System.out.printf("Date=%s [original date as a String]\r\n",sdt);
            System.out.printf("Date=%s [Date parsed from string]\r\n",df.format(dt));
            System.out.printf("Date=%s [Calendar-Default]\r\n",df.format(cal.getTime()));
            System.out.printf("Date=%s [Calendar-CST]\r\n",df.format(calCST.getTime()));
            System.out.printf("Date=%s [Calendar-PST]\r\n",df.format(calPST.getTime()));

            System.out.printf("Now set HOUR_OF_DAY to zero using cal.set(Calendar.HOUR_OF_DAY,0):\r\n");

            cal.set(Calendar.HOUR_OF_DAY,0);
            System.out.printf("Date=%s [Calendar-Default][Hour=0]\r\n",df.format(cal.getTime()));

            calCST.set(Calendar.HOUR_OF_DAY,0);
            System.out.printf("Date=%s [Calendar-CST ][Hour=0] <---BUG?\r\n",df.format(calCST.getTime()));

            calPST.set(Calendar.HOUR_OF_DAY,0);
            System.out.printf("Date=%s [Calendar-PST ][Hour=0] <---BUG?\r\n",df.format(calPST.getTime()));
            System.out.printf("----- HOUR_OF_DAY not as expected -----\r\n\r\n");
            }
        catch (Exception e) {
        }
    }
    
    public static void main(String[] args) {
        CalendarSetBug csb = new CalendarSetBug();
    }
    
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
suppose i could workaround if i need to, but seems a shame.

did play around with suggested intermixed calls to calendar's getTime() -- didn't change results for me


don't see anywhere else to post this so...many things i really like about using java, my hat's off to you guys, just surprised to see Calendar/Date stuff so cumbersome and at least for my use at the moment, buggy.