How To Convert GMT?

Question

I am working on an application. Every time a user (User A) submits an article or a message, the Greenwich time of the submission is stored in the database no matter which the time zone the user (User A) is.
Another user (User B who may be in another time zone) may later on retrieve the article or the message submitted by User A.
I want to display the User B local time of the Greenwich time saved in the database. How do I convert the GMT?

Answer 1

Hi Natalie,
you need to use time zones. Here is an example that creates a Calendar and then displays it in different time zones. Take a look at the java.sql.ResultSet API and you'll see that you have a getDate method that allows a Calendar to be specified.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.Calendar;
import java.util.TimeZone;
import java.text.DateFormat;
public class TimeZoneTest extends JFrame {
     private JTextField LocalTime = new JTextField(8);
     private JTextField GMT = new JTextField(8);
     private JTextField NewYorkTime = new JTextField(8);
     private JTextField TokyoTime = new JTextField(8);
     public static void main(String[] a){
          TimeZoneTest tzt = new TimeZoneTest();
     TimeZoneTest() {
          userInterface();
          // set times to now
          DateFormat showTime = DateFormat.getTimeInstance(DateFormat.MEDIUM);
          Calendar localCalendar = Calendar.getInstance();
          LocalTime.setText(showTime.format(localCalendar.getTime()));
          // do other time zones
          showTime.setTimeZone(TimeZone.getTimeZone("GMT"));
          GMT.setText(showTime.format(localCalendar.getTime()));
          showTime.setTimeZone(TimeZone.getTimeZone("America/New_York"));
          NewYorkTime.setText(showTime.format(localCalendar.getTime()));
          showTime.setTimeZone(TimeZone.getTimeZone("Asia/Tokyo"));
          TokyoTime.setText(showTime.format(localCalendar.getTime()));
     private void userInterface() {
          setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          setTitle("TimeZoneTest");
          Container cp = getContentPane();
          JPanel p = new JPanel(new GridLayout(4, 2));
          p.add(new JLabel("Local time"));
          p.add(LocalTime);
          p.add(new JLabel("GMT time"));
          p.add(GMT);
          p.add(new JLabel("N.York time"));
          p.add(NewYorkTime);
          p.add(new JLabel("Tokyo time"));
          p.add(TokyoTime);
          getContentPane().add(p);
          pack();
          setVisible(true);
}Hope this helps.
sjl