Countdown timer in java

[Peter Zagrzebski]

Hello I have two classes in java and am attempting to countdown to 0. I cannot change the code in minute second display and am having difficulty getting it to move from 10 to 0 on the display in minute second display because it calls invokeLater to Update the display and that does no get done until the end. If you could look at my code and give me any advice I would appreciate it.

package com.abc.countdown;

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

public class CountdownTimer extends JPanel {

    private MinuteSecondDisplay display;
    private int time;
    private Runnable count;
    private Thread t;

	
	public CountdownTimer() {
		display = new MinuteSecondDisplay();
		JButton startB = new JButton("Start");
		startB.addActionListener(new ActionListener() {
				public void actionPerformed(ActionEvent e) {
					// FIXME - call a method on the outer class to 
                    //         spawn a thread
				    
				    count = new Runnable() {
				        public void run() {
				     //   long currentTime = System.currentTimeMillis();
				        display.setSeconds(time);
				        }
				        }; 
				        countdown();
				        display.setSeconds(time);
				}
			});
		
		setLayout(new FlowLayout());
		add(startB);
		add(display);
		
	}
    
    // TODO - add methods to do the counting down and time correction....

	
	public void countdown() {
	    long normalSleepTime = 1000;
	    long nextSleepTime = normalSleepTime;
	    long totalSlept = 0;
	    time = 10;
	    int counter = 0;
	    t = new Thread(count);
        long startTime = System.currentTimeMillis();
        long startSlept = System.currentTimeMillis();
	    while(time > 0)
	    {      
	        try  {
	          
	            Thread.sleep(nextSleepTime);
	            System.out.println("Elapsed time " + (System.currentTimeMillis() - startTime));
	            SwingUtilities.invokeLater(count);
	        }catch (InterruptedException x ) {
	            
	        }
	        time--;
	        counter++;
	        long currentSleptTime = System.currentTimeMillis() - startSlept;
            nextSleepTime = (normalSleepTime * (counter + 1)) - (System.currentTimeMillis() - startTime);
            System.out.println("next Sleep time is " + nextSleepTime);
            startSlept = System.currentTimeMillis();
            if (nextSleepTime < 0) {
                nextSleepTime = 0;
            }

	        repaint();
	    }
	    System.out.println(System.currentTimeMillis() - startTime);
	}
	public static void main(String[] args) {
		JPanel p = new JPanel(new GridLayout(0, 1));
		p.add(new CountdownTimer());
		p.add(new CountdownTimer());
		p.add(new CountdownTimer());

		JFrame f = new JFrame("CountdownTimer Demo");
		f.setContentPane(p);
		f.pack();
		f.setVisible(true);
		f.addWindowListener(new WindowAdapter() {
				public void windowClosing(WindowEvent e) {
					System.exit(0);
				}
			}); 

	//      countdown();

	}
}

package com.abc.countdown;

import java.awt.*;
import javax.swing.*;
import java.text.*;

public class MinuteSecondDisplay extends JPanel {
	private static final Font TIME_FONT = new Font("Monospaced", Font.BOLD, 24);
	private static final NumberFormat FORMATTER;

	static {
		NumberFormat f = NumberFormat.getInstance();
		f.setMaximumFractionDigits(0);
		f.setMaximumIntegerDigits(2);
		f.setMinimumIntegerDigits(2);
		FORMATTER = f;
	}

	private volatile int seconds;
	private boolean delayOn;
	private Runnable updateTask;
	private JLabel timeL;
	
	public MinuteSecondDisplay() {
		seconds = 0;
		delayOn = true;

		updateTask = new Runnable() {
				public void run() {
				    System.out.println("calling update time label");
					updateTimeLabel();
				}
			}; 

		timeL = new JLabel("00:00", JLabel.CENTER);
		timeL.setFont(TIME_FONT);
		timeL.setForeground(Color.BLACK);
		updateTimeLabel();
		
		setLayout(new GridLayout()); 
		setBorder(BorderFactory.createEtchedBorder());
		add(timeL);
	}

	public void setSeconds(int seconds) {
		this.seconds = seconds;
		System.out.println("in minuteSecondDisplay");
		System.out.println(this.seconds);
		SwingUtilities.invokeLater(updateTask);

		if ( delayOn && ( seconds > 0 ) ) {
			// exaggerates time to run this method
			takeRandomMiniNap(); 
			System.out.println("done sleeping");
		}
	}

	private void takeRandomMiniNap() {
		try {
			// sleep for 0 to 99 ms
			long napTime = (long) (Math.random() * 100.0);
		    Thread.sleep(napTime); 
		} catch ( InterruptedException x ) {
			Thread.currentThread().interrupt(); // reassert intr
			return;
		}
	}
	
	private void updateTimeLabel() {
		int totalSec = seconds; // capture current value snapshot
		int sec = totalSec % 60;
		int min = (totalSec / 60) % 60;
		timeL.setText(FORMATTER.format(min) + ":" + FORMATTER.format(sec));
		System.out.println("updating timer now");
		
		
	}
}

[Steve Luke]

You are calling the countdown() method directly from the actionPerformed() method, which executes in your event dispatch thread - the same thread to used to draw on the screen. Since you are performing the Thread sleeping inside countdown the Event Thread won't be able to do the work it is intended to do - update the GUI.

So you should move the countdown() code to a different thread, so that the GUI interface isn't blocked while counting.

You are also doing some redundant context switching (with SwingUtilities.invokeLater() to call a method that itself uses SwingUtilities.invokeLater()), and creating objects you don't use (for example the t = new Thread(count)). So your code has a lot of clean-up which can be done.