JTextField不会使用Thread.sleep（）更新

Question

I'm trying to figure out why the text field isn't updating. I'm aware that using SwingWorker will probably fix this problem, but I can't understand why it doesn't work in the first place.

public class waitExample {

private JFrame frame;
private JTextField txtLeadingText;
private String one = "update string 1";
private String two = "update string 2";
private String three = "update string 3";

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

public waitExample() {
    initialize();
}

private void initialize() {
    frame = new JFrame();
    frame.setBounds(100, 100, 450, 300);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    txtLeadingText = new JTextField();
    txtLeadingText.setHorizontalAlignment(SwingConstants.CENTER);
    txtLeadingText.setText("leading text");
    frame.getContentPane().add(txtLeadingText, BorderLayout.SOUTH);
    txtLeadingText.setColumns(10);

    JButton btnClickMeTo = new JButton("CLICK ME TO UPDATE TEXT");
    btnClickMeTo.addMouseListener(new MouseAdapter() {
        @Override
        public void mouseClicked(MouseEvent arg0) {

            try {

                updateOne();
                Thread.sleep(1000);
                updateTwo();
                Thread.sleep(1000);
                updateThree();
                Thread.sleep(1000);
                updateLast();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    });
    frame.getContentPane().add(btnClickMeTo, BorderLayout.CENTER);
}

private void updateOne() {

    txtLeadingText.setText(one);
}

private void updateTwo() {

    txtLeadingText.setText(two);
}

private void updateThree() {

    txtLeadingText.setText(three);
}

private void updateLast() {

    txtLeadingText.setText("default text");
    }
}

From what I understand, the default Thread will prevent any GUI updates. That shouldn't matter because I am setting the textField BEFORE the Thread.sleep. Why doesn't the text field update? Shouldn't the text be set, then the Thread wait?

EDIT: As per the answers, the above code has been updated.

Answer 1

You are invoking Thread.sleep(1000); on EDT. This means that when your method will end - only then the repaint() will fire (at some point in time later).

Until then your GUI is freezed.

Consider that this is going on one thread (so processing is straightforward):

txtLeadingText.setText(one);
Thread.sleep(1000);
txtLeadingText.setText(two);
Thread.sleep(1000);
txtLeadingText.setText(three);
Thread.sleep(1000);
...
<returning from updateText()>
<processing other events on button click>
...
// some time later
<Swing finds out that GUI needs repaint: calls rapaint()>

This is what you should do (I didn't compile or test it):

    public class MyRunnable implements Runnable {
        private List<String> strsToSet;
        public MyRunnable(List<String> strsToSet) {
            this.strsToSet = strsToSet;
        }
        @Override
        public void run() {
            try {
                if(strsToSet.size() > 0) {
                    final String str = strsToSet.get(0);
                    SwingUtilities.invokeLater(new Runnable() {
                        @Override
                        public void run() {
                            txtLeadingText.setText(str);
                        }
                    });

                    Thread.sleep(1000);
                    List<String> newList = new LinkedList<String>(strsToSet);
                    newList.remove(0);
                    new Thread(new MyRunnable(newList)).start();
                }
            }
            catch(InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
    new Thread(new MyRunnable(Arrays.asList(one, two, three))).start();

It is hard to do in Swing but in contrast in dynamically languages (like Groovy) it would go as simple as that (you'll get a better grasp of what is going on):

    edt { 
        textField.setText(one)
        doOutside { 
            Thread.sleep(1000); 
            edt {
                textField.setText(two)
                doOutside { 
                    Thread.sleep(1000); 
                    edt {
                        textField.setText(three)
                    } 
                }
            } 
        }
    }

Answer 2

The GUI event loop updates the screen, but it can't update the screen until you return.

I suggest you avoid doing any blocking operations in the GUI event thread.