Question

I am trying to develop a game in an Applet and I am having this problem. I would like the display to show a countdown to the user before the game continues. However, the countdown will not display and is actually making the GUI freeze up instead. How can this be avoided? Here is some code demonstrating this problem.

EDIT: Code below ‘almost’ works, timer is going but screen will only update to new timer value whenever Start button is pressed. How can I make the text refresh automatically?

public class TestApplet extends JApplet implements ActionListener{


        final JTextField _displayField = new JTextField("Countdown", 6);
        CountDownTimer clock = new CountDownTimer();
        JButton jbtnStart = new JButton("Start");

    public void addComponentToPane(Container pane) {

        JPanel mainPanel = new JPanel();    
        mainPanel.add(jbtnStart);
        mainPanel.add(_displayField);
        pane.add(mainPanel);
        jbtnStart.addActionListener(this);
    }


  public void init() {

        TestApplet testApplet = new TestApplet();
        testApplet.setVisible(true);    
        testApplet.addComponentToPane(this.getContentPane());   
        this.setSize(200, 100);

}

    public void actionPerformed(ActionEvent e) {

      if ( e.getSource() == jbtnStart   ){
              clock.start(_displayField);
          }
   }     
}

// ********************************************************************************
//********************************************************************************
//********************************************************************************

class CountDownTimer  {

    private static final int N = 60;
    private final ClockListener cl = new ClockListener();
    private final Timer t = new Timer(1000, cl);
    static int count =0;

    public int getCount(){
         System.out.println(count);
        return count;
    }
    public void setCount(int n){
        count = n;
    }

    public CountDownTimer() {
        t.setInitialDelay(0);
    }

    public void start(JTextComponent c) {
        t.start();
       Boolean bool  = false;
          while ( bool ==false){     
              c.setText( "Starting new game in... "+ this.getCount() );
              bool = ( this.getCount()<10 );
          }
    }

    private class ClockListener implements ActionListener {

        public void actionPerformed(ActionEvent e) {
            count %= N;
            count++;
           setCount(count);
        }
    }
}

Answer 1

You have a while loop in the ActionListener that is blocking the EDT. The code to update the display field should not be in the ActionListener.

Instead this code should be in the Timer class. Then whenever the Timer fires you simply subtract one and update the display field. When the count reaches zero you stop the Timer.

Also, your CountDownTimer should not extend a JFrame. It is just a class and has nothing to do with a frame.

Edit:

Here is a simple usage of a Swing Timer:

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;

public class TimerTime extends JFrame implements ActionListener
{
    JLabel timeLabel;

    public TimerTime()
    {
        timeLabel = new JLabel( new Date().toString() );
        getContentPane().add(timeLabel, BorderLayout.NORTH);
    }

    public void actionPerformed(ActionEvent e)
    {
        timeLabel.setText( new Date().toString() );
    }

    public static void main(String[] args)
    {
        TimerTime frame = new TimerTime();
        frame.setDefaultCloseOperation( EXIT_ON_CLOSE );
        frame.pack();
        frame.setVisible(true);

        int time = 1000;
        javax.swing.Timer timer = new javax.swing.Timer(time, frame);
        timer.setInitialDelay(1);
        timer.start();
    }
}