Java（和 SwingUtilities）中的 GUI 线程

Question

I'm making a simple game in Java using swing and am having problems with my GUI freezing up sporadically (due to threading issues most probably) after a button press that is supposed to trigger a switch in JPanels.

I posted a related thread here , which has more details about the actual code I'm currently using (although I did update the countdown and get that working fine). From answers to that thread, it seems like using SwingUtilities.invokeLater() or invokeAndWait() might be what I need to solve the problem, but I'm not sure where in my code it is necessary or exactly how to implement it.

I don't know that much about threading and could use any help (preferably somewhat detailed and with some sample code) that I can get. Let me know if any further details would be useful.

Answer 1

See: Tutorial: Concurrency in Swing

Generally speaking, the Event Dispatch Thread is a single thread, chugging through the event queue, processing one at a time.

SwingUtilities.invokeLater(..) 

puts a Runnable on this queue. So it will be processed by the EDT when the EDT finishes everything on the queue before it (This is why sleeping on the queue blocks other events like repainting). It's relatively unusual to call invokeLater(..) from the EDT itself, though there are situations where it is useful (usually as a hack). I don't think I have had a legitimate use for SwingUtilities.invokeAndWait(..) in the last 6 years. Maybe once.

javax.swing.Timer can be configured to fire once or periodically. When it fires, it puts an event on the EDT queue. If you have computationally-intensive processing that need to be done, consider using javax.swing.SwingWorker to do the computation on another thread, and give you back the result in a thread-safe manner (this is also comparatively rare).

Answer 2

I have create a WorkerThread class which take care of Threads and GUI current/main thread . i have put my GUI application in construct() method of WorkerThread when an event fire to start XXXServer then all threads are activate and GUI work smoothlly wihout freeze. have a look. /** * Action Event * * @see java.awt.event.ActionListener#actionPerformed(java.awt.event.ActionEvent) */ public void actionPerformed(ActionEvent ae) { log.info("actionPerformed begin..." + ae.getActionCommand());

    try {
        if (ae.getActionCommand().equals(btnStart.getText())) {
             final int portNumber = 9990;
             try {

                 WorkerThread workerThread = new WorkerThread(){
                    public Object construct(){

                        log.info("Initializing the XXXServer ...");
                        // initializing the Socket Server
                         try {
                            XXXServer xxxServer = new XXXServer(portNumber);
                            xxxServer.start();
                            btnStart.setEnabled(false);                             
                        } catch (IOException e) {
                            // TODO Auto-generated catch block
                            log.info("actionPerformed() Start button ERROR IOEXCEPTION..." + e.getMessage());
                            e.printStackTrace();
                        }
                        return null;
                    }
                };workerThread.start();
                } catch (Exception e) {
                    log.info("actionPerformed() Start button ERROR..." + e.getMessage());
                    e.printStackTrace();
             }


        } else if (ae.getActionCommand().equals(btnStop.getText())) {
            log.info("Exit..." + btnStop.getText());
            closeWindow();
        }

    } catch (Exception e) {
        log
            .info("Error in ServerGUI actionPerformed==="
                + e.getMessage());
    }

}

Answer 3

In order to invoke an action in the existing WorkerThread, one would intuitively send a user defined event using SwingUtilities.invokeLater() to a JFrame's actionPerformed() method as

class TestFrame extends JFrame implements ActionListener
{
...

    private class Performer implements Runnable
    {
        ActionEvent event;

        Performer(ActionEvent event)
        {
            this.event = event;
        }

        @Override
        public void run()
        {
            actionPerformed(event);
        }

    }

    synchronized protected void invokeLater(ActionEvent event)
    {
        SwingUtilities.invokeLater(new Performer(event));
    }

    public void actionPerformed(ActionEvent event)
    {
        ...
    }

}

Now, TestFrame.invokeLater() called in any Thread will be processed in TestFrame.actionPerformed() in existing WorkerThread .

Answer 4

A good point to look is the docs . In your case, this explains how SwingUtilities.invokeLater() works and where to use it:

Causes doRun.run() to be executed asynchronously on the AWT event dispatching thread. This method should be used when an application thread needs to update the GUI .

So, in your actions that modifies the GUI you must use the invokeLater method to assure that the GUI wont freeze.

Another good resource is the Java tutorials. They cover concurrency in Swing .

Answer 5

If you have some work defined in your GUI code like this

Runnable doWorkRunnable = new Runnable() {
    @Override
    public void run() { 
        doWork(); 
    }
};

And you are calling it by attaching it to a new Thread

Thread t = new Thread(doWorkRunnable);
t.start();

You are executing your work in GUI thread, which will cause problems in a Swing application.

Instead try this (let me mention this is just an example of usage)

SwingUtilities.invokeLater(doWorkRunnable);

This puts your Runnable worker to the AWT Event Queue, and will execute it when previous events are finished.

EDIT : Here's the complete example which executes countdown from 3 to 0 and then does whatever you want to do after countdown.

public class TestFrame extends JFrame {

    private JPanel contentPane;
    private final Timer timer;
    private TimerTask[] tasks;

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    TestFrame frame = new TestFrame();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    public TestFrame() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 450, 300);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        contentPane.setLayout(new BorderLayout(0, 0));
        final JLabel lblCountdown = new JLabel();
        contentPane.add(lblCountdown, BorderLayout.NORTH);
        JButton btnStart = new JButton("Start");
        contentPane.add(btnStart, BorderLayout.SOUTH);

        timer = new Timer();
        tasks = new TimerTask[4];

        setContentPane(contentPane);

        for (int i = 0; i < 4; i++) {
            final int count = i;
            tasks[i] = new TimerTask() {
                public void run() {
                    EventQueue.invokeLater(new Runnable() {
                        @Override
                        public void run() {
                            lblCountdown.setText(count + "");
                        }
                    });
                }
            };
        }

        btnStart.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {

                for (int i = 0; i < 4; i++) {
                    timer.schedule(tasks[4 - i - 1], (1000 * i), (1000 * (i + 1)));
                }
                // add another timer.schedule(TimerTask)
                // to execute that "move to game screen" task
                TimerTask taskGotoGame = new TimerTask() {
                    public void run() {
                        timer.cancel();
                        JOptionPane.showMessageDialog(null, "Go to game", "Will now", JOptionPane.INFORMATION_MESSAGE);
                        System.exit(0);
                    }
                };
                // and schedule it to happen after ROUGHLY 3 seconds
                timer.schedule(taskGotoGame, 3000);
            }
        });

    }

}