Use of Timezone and method inDaylightTime

Question

I'm trying to find date and time for DST start for a timezone. I use Java classes TimeZone and GregorianCalendar. To find out which date and time is DST I use the method timeZone.inDaylightTime(date). The code that is shown below finds the correct date, but I can't get time of day when DST starts correct. (I know that date/time of timeZone.inDaylightTime(date)is GMT time). Can anybody help me?
Code example:
GregorianCalendar gc = new GregorianCalendar(year,GregorianCalendar.JANUARY,1);
int hour =0;
//Run through all months of year
for (int i = 0; i <= gc.getActualMaximum(GregorianCalendar.MONTH); i++)
//Run through each day of the month
for (int a = 0; a < gc.getActualMaximum(GregorianCalendar.DAY_OF_MONTH); a++)
//Run through the hours
for (int s=0; s<24; s++) {
gc.set(GregorianCalendar.HOUR_OF_DAY,hour);
startDate = gc.getTime();
if (timeZone.inDaylightTime(startDate)) {
found = true;
break;
hour = hour + 1;
if (found) {
break;
}//end running through hours
//Get next day of month
hour = 0;
gc.roll(GregorianCalendar.DAY_OF_MONTH, true);
if (found) {
break;
gc.set(GregorianCalendar.DAY_OF_MONTH, 1);
gc.roll(GregorianCalendar.MONTH, true);

Answer 1

If I for example use timezone Europe/Oslo I expect the
loop to stop on date 30.mar.2003 at 01:00. (DST start
02:00 local time).There are two problems with this. First, your program stops when it encounters a date that IS in DST. 01:00 is not in DST, so why would it stop there? It stops at 02:00... which is where the second problem comes in. There are two names for this particular instance in time -- 02:00 standard time and 03:00 daylight saving time. Java chooses to use the latter, so your program stops when it encounters 03:00, daylight saving time.
Then I would add one hour (which
is the rawoffset (timeZone.rawoffset)) to the given
timezone to get local time.What does raw offset have to do with this? That's the difference between the local time and GMT, not the number of hours that the clock moves forward when daylight saving time starts.
I use Could there be a bug in jdk1.3.1_02, could there
be a bug??Don't think so. Try this change to your program: addDateFormat df = DateFormat.getInstance();
df.setTimeZone(timeZone);at the beginning, andSystem.out.println("Try " + df.format(startDate));just before you test inDaylightTime(startDate). You'll see that the hours increase by 1 except that the last date displayed appears to be 2 hours after its predecessor. As I explained earlier, it really isn't, that's just the daylight saving change.