JProgressBar pb

Question

why this code doesn't work ???
//initialise button ...
JButton action = new JButton("go");
JProgressBar progressBar = new JProgressBar();
action.addActionListener(this);
public void actionPerformed(ActionEvent arg0)
          if(arg0.getSource() == action)
showProgressBar(true);
try
                    Thread.currentThread().sleep(3500);
          } catch (InterruptedException e1)
                    e1.printStackTrace();
               //showProgressBar(false);
public void showProgressBar(boolean state)
          progressBar.setString("Working ...");
          progressBar.setIndeterminate(state);
          progressBar.setStringPainted(state);
in fact , the problem is the JProgressBar only start after the sleep ( if i put showProgressBar(false) in comment ) and not while .
regards,vashuu

Answer 1

In swing, the rule is that you may only update a gui via the event dispatch thread. You put it to sleep in your code with 'Thread.currentThread().sleep(3500);' so no updates are possible until the event queue clears down to the update request. To be able to update the gui start and run your process in another thread. This will leave the edt free to process your update requests as they are received. Torgil has given a pointer to the entry-point resource to learn about this.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class ProgressBarTest extends JPanel
    JProgressBar progressBar;
    JButton start;
    boolean continueTask;
    public ProgressBarTest()
        initComponents();
        continueTask = false;
        setLayout(new BorderLayout());
        JPanel panel = new JPanel();
        panel.add(start);
        add(panel, "North");
        panel = new JPanel();
        panel.add(progressBar);
        add(panel, "South");
    private void initComponents()
        progressBar = new JProgressBar(JProgressBar.HORIZONTAL,0,100);
        progressBar.setStringPainted(true);
        Dimension d = progressBar.getPreferredSize();
        d.height = 20;
        progressBar.setPreferredSize(d);
        start = new JButton("start");
        start.addActionListener(new ActionListener()
            public void actionPerformed(ActionEvent e)
                System.out.println("in listener: isEventDispatchThread = " +
                                   SwingUtilities.isEventDispatchThread());
                startProcess();
    private void startProcess()
        if(continueTask)
            return;
        new Thread(new Runnable()  // not the event dispatch thread
            public void run()
                System.out.println("in process : isEventDispatchThread = " +
                                   SwingUtilities.isEventDispatchThread());
                int count = 0;
                continueTask = true;
                while(continueTask)
                    int max = progressBar.getMaximum();
                    int value = (int)((++count * 100.0) / max);
                    progressBar.setValue(value);
                    try
                        Thread.sleep(250);
                    catch(InterruptedException ie)
                        System.err.println("interruption: " + ie.getMessage());
                        continueTask = false;
                    if(value >= max)
                        continueTask = false;
                        progressBar.setValue(0);
        }).start();
    public static void main(String[] args)
        // JFrame code can go here
        f.getContentPane().add(new ProgressBarTest());
}