进度条问题ProgressMonitor

Java code

import java.awt.Button;
import javax.swing.JFrame;
import javax.swing.ProgressMonitor;

public class Progress extends JFrame {
         private ProgressMonitor pm = new ProgressMonitor(this,"Monitoring Progress","Test",0,100);
         Button but = new Button("点击");
    public Progress(){
        pm.setProgress(0);
        pm.setMillisToPopup(1000);
        this.add(but);
        but.addActionListener(new ActionListener(){
                           public void actionPerformed(ActionEvent arg0) {
                for(int i = 0;i<101;i++){//设置断点，一步一步循环
                    pm.setProgress(i);
                }
                
            }    
        });
        this.setSize(300,200);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setVisible(true);
    }
    public static void main(String[] args) {
        new Progress();
    }    
}

设置断点后点击按钮，运行到pm.setProgress(i)时，有个框出来，但不是正常的，里面什么都没，而且还卡住了
为什么？请各位指教，谢谢咯

------解决方案--------------------
google了个例子。。


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

public class ProgressMonitorDemo extends JPanel
implements ActionListener {
public final static int ONE_SECOND = 1000;

private ProgressMonitor progressMonitor;
private Timer timer;
private JButton startButton;
private LongTask task;
private JTextArea taskOutput;
private String newline = "\n";

public ProgressMonitorDemo() {
super(new BorderLayout());
task = new LongTask();

//Create the demo's UI.
startButton = new JButton("Start");
startButton.setActionCommand("start");
startButton.addActionListener(this);

taskOutput = new JTextArea(5, 20);
taskOutput.setMargin(new Insets(5,5,5,5));
taskOutput.setEditable(false);

add(startButton, BorderLayout.PAGE_START);
add(new JScrollPane(taskOutput), BorderLayout.CENTER);
setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));

//Create a timer.
timer = new Timer(ONE_SECOND, new TimerListener());
}

class TimerListener implements ActionListener {
public void actionPerformed(ActionEvent evt) {
progressMonitor.setProgress(task.getCurrent());
String s = task.getMessage();
if (s != null) {
progressMonitor.setNote(s);
taskOutput.append(s + newline);
taskOutput.setCaretPosition(
taskOutput.getDocument().getLength());
}
if (progressMonitor.isCanceled() || task.isDone()) {
progressMonitor.close();
task.stop();
Toolkit.getDefaultToolkit().beep();
timer.stop();
if (task.isDone()) {
taskOutput.append("Task completed." + newline);
} else {
taskOutput.append("Task canceled." + newline);

}
startButton.setEnabled(true);
}
}
}

public void actionPerformed(ActionEvent evt) {
progressMonitor = new ProgressMonitor(ProgressMonitorDemo.this,
"Running a Long Task",
"", 0, task.getLengthOfTask());
progressMonitor.setProgress(0);
progressMonitor.setMillisToDecideToPopup(2 * ONE_SECOND);

startButton.setEnabled(false);