Java Swing如何使这个计数器工作？

Question

Everytime my counter reaches 4 I want it to play a beep sound and go back to '1' and again count up to 4 play the beep sound and so on.

I probably shouldn't place this in a label, because the counter doesnt run at all! I don't get any errors but the label says; counter is 4 and doesnt count or anything.

Can you help me make this counter work properly? I also used printline but that gave some errors too.

My code for the counter is this:

button1.addActionListener(new ActionListener() {

  public void actionPerformed(ActionEvent arg0) {

    label1.setVisible(true);
    int counter = 1;

    while(counter < 5 )
    {
      label1.setText("counter  is " + counter);
      counter = counter + 1 ;
    }

    counter = 1;
    tk.beep();
  }
});

Answer 1

Spawn a new thread to count, wait, and update the GUI.

You're doing all of this work in the Event Dispatch Thread, which is the only thread which updates the GUI. So when you set the text of the label, it doesn't get updated on the screen until the method returns and the Event Dispatch Thread handles the repaint operation.

You need to spawn a new thread to do this, rather than just running it in a loop which executes immediately. Just have the actionPerformed method spawn a new Thread which handles this instead. Loop, count, and update in this thread, waiting with Thread.sleep between updates. To update the label text, create a new Runnable that will update the label to the next value and put it on the Event Dispatch Thread with SwingUtilities.invokeLater . Keep this thread running in the background until you need it. I would recommend checking a shutdown status boolean every loop through, and quitting when it's set to false. This way, you can shut down the thread cleanly at any time. Or, if you want it to countdown and beep only once, you can have the thread just end after one iteration of counting.

There are lots of questions on Stack Overflow that detail each of these steps, so I won't repeat this information here.

• How does the event dispatch thread work?
• How to create the thread which does the counting

Answer 2

After changing the value you need to repaint. Also, I assume you actually want to count the seconds in which case you need to use a Timer to kick off the action of changing the label and possibly playing a sound.

Answer 3

Maybe this is does what you intened, every 4th button press it resets and beeps

loginButton.addActionListener(new java.awt.event.ActionListener() {

    int counter = 1;

    public void actionPerformed(ActionEvent arg0) {

        label1.setVisible(true);

        if (counter < 5) {
            label1.setText("counter  is " + counter);
            label1.repaint();
            ++counter;
        } else {
            counter = 1;
            tk.beep();
        }
    }
});

Answer 4

If I understand correctly what you want , the below code should accomplish your goal.

button1.addActionListener(new ActionListener() {

  public void actionPerformed(ActionEvent arg0) {

    label1.setVisible(true);

    Runnable runnable = new Runnable() {
           int counter =1 ;

           public void run() {
               while(true) {

                    while (counter<5)  {
                        SwingUtilties.invokeLater(new Runnable() {
                               public void run() {
                                   label1.setText("counter  is " + counter);
                               }
                        }); 

                        counter = counter + 1 ;
                        try {
                           Thread.sleep(1000);
                        }catch(InterruptedException ex) {
                            System.err.println(ex.toString());

                        }    
                    } 
                counter = 1;
                tk.beep();

                }

           }
    };

     new Thread(runnable).start();

});

Answer 5

Your loop stops after the first 4 and never called again. since the text is changing to fast, you can only see the last result

int counter = 0;
while (//when do you want it to stop?)
{
    // print what you want (using (counter % 4) + 1)
    if ((counter % 4) == 0)
    {
         tk.beep();
    }
}