Question

I am creating a Java GUI on a clock which asks the user to change the time from current time. I have the system time and the user time. What should be the code so that the user time gets displayed. The foolowing code i am using :

        Date curDate = new Date();
        //changeTime i have got from the user
        double time=0;
        if(curDate.getTime()- changeTime.getTime() > 0){
            time = curDate.getTime() - changeTime.getTime();
            time = time/(1000);
        }
        else{
            time = changeTime.getTime()-curDate.getTime();
            time = time/(1000);
        }
        if(changeTime.getHours()==0 && changeTime.getMinutes()==0){
            time=0;
        }
        curDate.setHours(curDate.getHours()+(int)time/(3600));
        curDate.setMinutes(curDate.getMinutes()+((int)time/60)%60);

Answer 1

A new Date() is “intended to reflect coordinated universal time (UTC).” What the user sees on the clock depends on the TimeZone, which can be specified in the DateFormat used to render the date. The example below prints the same instant in GMT and a selection of time zones from New York to Berlin.

Addendum: I find it helpful to think of Date as a model and DateFormat as a view of that model.

03-Feb-2013 18:01:42 GMT GMT 1359914502673
03-Feb-2013 13:01:42 EST America/New_York 1359914502673
03-Feb-2013 14:01:42 AST America/Aruba 1359914502673
03-Feb-2013 15:01:42 ART America/Buenos_Aires 1359914502673
03-Feb-2013 16:01:42 BRST America/Sao_Paulo 1359914502673
03-Feb-2013 17:01:42 AZOT Atlantic/Azores 1359914502673
03-Feb-2013 18:01:42 GMT Europe/London 1359914502673
03-Feb-2013 19:01:42 CET Europe/Berlin 1359914502673

package date;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.TimeZone;

/** @see http://stackoverflow.com/a/14675418/230513 */
public class TestSDF {

    private static final String s = "dd-MMM-yyyy HH:mm:ss zz";
    private static final DateFormat f = new SimpleDateFormat(s);

    public static void main(String[] args) {
        Date date = new Date();
        print("GMT", date);
        print("America/New_York", date);
        print("America/Aruba", date);
        print("America/Buenos_Aires", date);
        print("America/Sao_Paulo", date);
        print("Atlantic/Azores", date);
        print("Europe/London", date);
        print("Europe/Berlin", date);
    }

    private static void print(String tz, Date d) {
        f.setTimeZone(TimeZone.getTimeZone(tz));
        System.out.println(f.format(d)
            + " " + tz
            + " " + d.getTime());
    }
}