Change Date value from one TimeZone to another TimeZone - calendar

Question

my case is I have a Date obj the date inside is UTC time. However I want it to be changed to Japan time.
Calendar calendar = Calendar.getInstance(TimeZone.getTimeZone("Japan"));
calendar.setTime(someExistingDateObj);
System.out.println(String.valueOf(calendar.get(Calendar.HOUR_OF_DAY)) + ":" + calendar.get(Calendar.MINUTE));
the existingDateObj is mapped from db and db value is 2013-02-14 03:37:00.733
04:37
it seems the timezone is not working?
thanks for your time....

Answer 1

Your problem may be that you're looking at things wrong. A Date doesn't have a time zone. It represents a discrete moment in time and is "intended to reflect coordinated universal time". Calendars and date formatters are what get time zone information. Your second example with the Calendar and TimeZone instances appears to work fine. Right now, this code:
public static void main(String[] args) {
Calendar calendar = Calendar.getInstance(TimeZone.getTimeZone("Japan"));
System.out.println(String.valueOf(calendar.get(Calendar.HOUR)) + ":" + calendar.get(Calendar.MINUTE));
}
Reports:
0:32
That appears correct to me. What do you find wrong with it?
Update: Oh, perhaps you're expecting 12:32 from the above code? You'd want to use Calendar.HOUR_OF_DAY instead of Calendar.HOUR for that, or else do some hour math. Calendar.HOUR uses 0 to represent both noon and midnight.
Update 2: Here's my final attempt to try to get this across. Try this code:
public static void main(String[] args) {
Calendar calendar = Calendar.getInstance();
SimpleDateFormat format = new SimpleDateFormat("H:mm a Z");
List<TimeZone> zones = Arrays.asList(
TimeZone.getTimeZone("CST"),
TimeZone.getTimeZone("UTC"),
TimeZone.getTimeZone("Asia/Shanghai"),
TimeZone.getTimeZone("Japan"));
for (TimeZone zone : zones) {
calendar.setTimeZone(zone);
format.setTimeZone(zone);
System.out.println(
calendar.get(Calendar.HOUR_OF_DAY) + ":"
+ calendar.get(Calendar.MINUTE) + " "
+ (calendar.get(Calendar.AM_PM) == 0 ? "AM " : "PM ")
+ (calendar.get(Calendar.ZONE_OFFSET) / 1000 / 60 / 60));
System.out.println(format.format(calendar.getTime()));
}
}
Note that it creates a single Calendar object, representing "right now". Then it prints out the time represented by that calendar in four different time zones, using both the Calendar.get() method and a SimpleDateFormat to show that you get the same result both ways. The output of that right now is:
22:59 PM -6
22:59 PM -0600
4:59 AM 0
4:59 AM +0000
12:59 PM 8
12:59 PM +0800
13:59 PM 9
13:59 PM +0900
If you used Calendar.HOUR instead of Calendar.HOUR_OF_DAY, then you'd see this instead:
10:59 PM -6
22:59 PM -0600
4:59 AM 0
4:59 AM +0000
0:59 PM 8
12:59 PM +0800
1:59 PM 9
13:59 PM +0900
It correctly shows the current times in Central Standard Time (my time zone), UTC, Shanghai time, and Japan time, respectively, along with their time zone offsets. You can see that they all line up and have the correct offsets.

Answer 2

sdf2 and sdf3 are equaly initialized, so there is no need for two of them.