Java: Flash a window to grab user's attention

Question

Is there a better way to flash a window in Java than this:

public static void flashWindow(JFrame frame) throws InterruptedException {
     int sleepTime = 50;
     frame.setVisible(false);
     Thread.sleep(sleepTime);
     frame.setVisible(true);
     Thread.sleep(sleepTime);
     frame.setVisible(false);
     Thread.sleep(sleepTime);
     frame.setVisible(true);
     Thread.sleep(sleepTime);
     frame.setVisible(false);
     Thread.sleep(sleepTime);
     frame.setVisible(true);
}

I know that this code is scary...But it works alright. (I should implement a loop...)

Answer 1

Well, there are a few minor improvements we could make. ;)

I would use a Timer to make sure callers don't have to wait for the method to return. And preventing more than one flashing operation at a time on a given window would be nice too.

import java.util.Map;
import java.util.Timer;
import java.util.TimerTask;
import java.util.concurrent.ConcurrentHashMap;
import javax.swing.JFrame;

public class WindowFlasher {

    private final Timer timer = new Timer();
    private final Map<JFrame, TimerTask> flashing
                              = new ConcurrentHashMap<JFrame, TimerTask>();

    public void flashWindow(final JFrame window,
                            final long period,
                            final int blinks) {
        TimerTask newTask = new TimerTask() {
            private int remaining = blinks * 2;

            @Override
            public void run() {
                if (remaining-- > 0)
                    window.setVisible(!window.isVisible());
                else {
                    window.setVisible(true);
                    cancel();
                }
            }

            @Override
            public boolean cancel() {
                flashing.remove(this);
                return super.cancel();
            }
        };
        TimerTask oldTask = flashing.put(window, newTask);

        // if the window is already flashing, cancel the old task
        if (oldTask != null)
            oldTask.cancel();
        timer.schedule(newTask, 0, period);
    }
}

Answer 2

Please don't vote up Professor Internet's answer -- he posted a few times with fake/misleading information. That one just seems to have slipped through the cracks. It is certainly not industry standard.

There are two common ways to do this: use JNI to set urgency hints on the taskbar's window, and create a notification icon/message. I prefer the second way, since it's cross-platform and less annoying.

See documentation on the TrayIcon class, particularly the displayMessage() method.

The following links may be of interest:

• New System Tray Functionality in Java SE 6
• Java Programming - Iconified window blinking
• TrayIcon for earlier versions of Java