How to add real-time date and time into a JFrame component e.g. "status bar"?

Question

Like the one we add into the corner of presentation slides.

I already have SwingX library added and working, in case that could help with something.

Answer 1

Basically, you want to use a JLabel for displaying the date/time, a javax.swing.Timer set to a regular interval to update the label and a DateFormat instance to format the date value...

public class PlaySchoolClock {

    public static void main(String[] args) {
        new PlaySchoolClock();
    }

    public PlaySchoolClock() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException ex) {
                } catch (InstantiationException ex) {
                } catch (IllegalAccessException ex) {
                } catch (UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Test");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new ClockPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class ClockPane extends JPanel {

        private JLabel clock;

        public ClockPane() {
            setLayout(new BorderLayout());
            clock = new JLabel();
            clock.setHorizontalAlignment(JLabel.CENTER);
            clock.setFont(UIManager.getFont("Label.font").deriveFont(Font.BOLD, 48f));
            tickTock();
            add(clock);

            Timer timer = new Timer(500, new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    tickTock();
                }
            });
            timer.setRepeats(true);
            timer.setCoalesce(true);
            timer.setInitialDelay(0);
            timer.start();
        }

        public void tickTock() {
            clock.setText(DateFormat.getDateTimeInstance().format(new Date()));
        }
    }
}

This example uses a time interval of half a second. The main reason for this is I don't go to the trouble of trying to calculate how far we are away from the next second when we set up the initial delay. This ensures that we are always up-to-date

The next question is to ask "why?" This kind of setup is relatively expensive, with the timer firing every half second (to catch any edge cases) and updating the screen, when most OS's actually have a date/time already on the screen...IMHO