Java Swing Concurrency display JTextArea

I need to execute/display a series of events from a Arraylist to a JTextArea, however, each Even开发者_如何学Got gets execute with different time. Following is a quick example of my goal:

public void start(ActionEvent e)
 {
  SwingUtilities.invokeLater(new Runnable()
  {
   public void run()

   {
    jTextArea.append("Test" + "\n");
    try
    {
     Thread.sleep(3000);
    } catch (InterruptedException e1)
    {
     e1.printStackTrace();
    }
    jTextArea.append("Test1" + "\n");
   }
  });
 }

So right now, "Test" and "Test1" display on JTextArea after whole execution is completed. How do I make "Test" display first, then 3 secs later, display "Test1"

Thank u all in advance

---

invokeLater schedules the runnable to run on the Event Dispatch Thread. You shouldn't sleep within it or you will starve the dispatch thread. Try using a separate worker thread instead:

Thread worker = new Thread(new Runnable(){
    public void run(){
        jTextArea.append("Test" + "\n");
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e1) {
            e1.printStackTrace();
        }
        jTextArea.append("Test1" + "\n");

    }
});
worker.start();

---

If your tasks are time/cpu intensive, then yes, definitely use a background thread to do this such as a SwingWorker object or a Runnable run in a Thread. If however what you need to do is to stagger the display of something and all you are looking for is the Swing equivalent of Thread.sleep(3000), then your best option is to use a Swing Timer. There is an excellent tutorial on how to use these which you can find here: http://download.oracle.com/javase/tutorial/uiswing/misc/timer.html

For example:

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

 public class Fu extends JPanel {
      private static final int TIMER_DELAY = 600;
      protected static final int MAX_COUNT = 20;
      private JTextArea jTextArea = new JTextArea(10, 10);
      private JButton startBtn = new JButton("Start");
      private Timer timer;

      public Fu() {
           startBtn.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                     startAction(e);
                }
           });

           add(new JScrollPane(jTextArea, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, 
                     JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED));
           add(startBtn);
      }

      private void startAction(ActionEvent e) {
           if (timer != null && timer.isRunning()) {
                // prevent multiple instances of timer from running at same time
                return;
           }
           timer = new Timer(TIMER_DELAY, new ActionListener() {
                private int count = 0;
                public void actionPerformed(ActionEvent e) {
                     if (count < MAX_COUNT) {
                          count++;
                          jTextArea.append("Test " + count + "\n");
                     } else {
                          jTextArea.append("Done! \n");
                          timer.stop();
                          timer = null;
                     }
                }
           });
           timer.setInitialDelay(0);
           timer.start();
      }

      public static void main(String[] args) {
           SwingUtilities.invokeLater(new Runnable() {
                public void run() {
                     JFrame frame = new JFrame("Foo");
                     frame.getContentPane().add(new Fu());
                     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                     frame.pack();
                     frame.setLocationRelativeTo(null);
                     frame.setVisible(true);
                }
           });
      }
 }

---

As pointed out, this is a bad idea, as you will block the event thread.

However, understanding the reason for this is important as well. As you seem to know, all code that affects the state of Swing components needs to happen in the event handling thread (which is the reason why invokeLater and friends should always be used).

What is a bit less better known is that paining code also executes in the event handling thread. When your call to Thread.sleep is executing, it's not only blocking the event thread, it's also blocking any painting of components. This is why the full update appears to happen in one go -- the JTextArea is updated but it can't be repainted until your run method returns.

Lots of info available here: http://java.sun.com/products/jfc/tsc/articles/threads/threads1.html