Q:

how to put a timer on a JLabel to update itself every second

I created a game and in my swing GUI interface I want to put a timer. The way I do this at the moment is have a field with the current time , gotten with System.currentTimeMillis() which gets it's value when the game starts .In the method of my game i put the   System.currentTimeMillis()- field; and it tells you the current time passed since the game started.
Nevertheless, how do get this  to update itself every second lets say, so the JLabel will have : timePassed: 0s , timePassed: 1s and so on. Have in mind that i don't use threads in my game at any point.
EDIT: thank you all for your kind suggestions. I used a combination of your answers please give me some feedback.
I have the JLabel as a field called time. (else i cant handle it).
time = new JLabel("Time Passed:  " + timePassed() + " sec");
panel_4.add(time);

ActionListener actionListener = new ActionListener() {
    public void actionPerformed(ActionEvent actionEvent) {
        time.setText("Time Passed: " + timePassed() + " sec");
    }
};

Timer timer = new Timer(1000, actionListener);
timer.start();

A:

Have a look at the swing timer class. It allows to setup recurring tasks quite easily.

A:

This is how I would set my JLabel to update with time & date.
Timer SimpleTimer = new Timer(1000, new ActionListener(){
    @Override
    public void actionPerformed(ActionEvent e) {
        jLabel1.setText(SimpleDay.format(new Date()));
        jLabel2.setText(SimpleDate.format(new Date()));
        jLabel3.setText(SimpleTime.format(new Date()));
    }
});
SimpleTimer.start();

This is then added to your main class and the jlabel1/2/3 get updated with the timer.

A:

new Thread(new Runnable
{
    public void run()
    {
        long start = System.currentTimeMillis();
        while (true)
        {
            long time = System.currentTimeMillis() - start;
            int seconds = time / 1000;
            SwingUtilities.invokeLater(new Runnable() {
                 public void run()
                 {
                       label.setText("Time Passed: " + seconds);
                 }
            });
            try { Thread.sleep(100); } catch(Exception e) {}
        }
    }
}).start();

