Progress bar and threads

Question

I have made a web browser, when you load a web-page a progress bar is displayed showing the current progress of the page loading. However if you try and load a new page before the previous page has finished loading the progress bar goes crazy. I have included a short example of what is happening below:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
//import javax.swing.event.*;
public class ProgressBarTest extends JFrame implements ActionListener,Runnable{
    private JProgressBar myprogressBar;
    private boolean stopProgressBar = false;
    public Thread thread;
    public ProgressBarTest(){
        createGui();
    }//end of constructor
    public void createGui(){
        this.setLayout(new BorderLayout());
        this.setDefaultCloseOperation(this.EXIT_ON_CLOSE);
        this.setSize(300,150);
        JPanel ButtonPanel = new JPanel(new FlowLayout());
        JButton new_Page = new JButton("new Page");
        JButton Page_Loaded = new JButton("Page Loaded");
        new_Page.addActionListener(this);
        Page_Loaded.addActionListener(this);
        ButtonPanel.add(new_Page);
        ButtonPanel.add(Page_Loaded);
        myprogressBar = new JProgressBar(0,100);
        this.add(ButtonPanel,BorderLayout.NORTH);
        this.add(myprogressBar,BorderLayout.CENTER);
        this.setVisible(true);
    }//end of method
    public void actionPerformed(ActionEvent e) {
        if(e.getActionCommand().equals("new Page")){
            createNewandRun();
        }else if(e.getActionCommand().equals("Page Loaded")){
            stopProgressBar = true;
    }//end of method
    public void run(){
            myprogressBar.setVisible(true);
            stopProgressBar = false;
            myprogressBar.setValue(0);
            System.out.println("Page Loading...");
            try{
                for(int i = 0;i<100;i++){
                    Thread.sleep(70);
                    myprogressBar.setValue(i);
                    if(stopProgressBar){
                        System.out.println("progress was stopeed at "+i+ " %");
                        break;
              myprogressBar.setValue(100);
              System.out.println("Page Loaded");
              thread.sleep(1000); //Show complete progress bar for one second
            }catch (Exception e){
                System.out.println("thread error "+e);
           myprogressBar.setVisible(false);
    }//end of run method
    public void createNewandRun(){
      thread = new Thread(this);
      thread.start();
    public static void main(String args[]){
         SwingUtilities.invokeLater(new Runnable() {
         @Override
         public void run() {
          new ProgressBarTest();
    }//end of main
}//end of classThanks in advance
Calypso

Answer 1

Using Swing Worker.... Just like your code intended, the progress bar will wait one second upon completion before being made invisible. If the "New Page" button is pressed then the old SwingWorker exits gracefully and a new one starts up. All modification of the JProgressBar is done on the Event Dispatching Thread.
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JButton;
import javax.swing.JProgressBar;
import javax.swing.SwingWorker;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeEvent;
public class ProgressBarTest implements ActionListener,
        PropertyChangeListener{
    JButton newPage;
    JButton pageLoaded;
    JProgressBar progressBar;
    PageLoader currentWorker;
    public ProgressBarTest() {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        newPage = new JButton("New Page");
        newPage.addActionListener(this);
        pageLoaded = new JButton("Page Loaded");
        pageLoaded.addActionListener(this);
        JPanel buttonPanel = new JPanel();
        buttonPanel.add(newPage);
        buttonPanel.add(pageLoaded);
        progressBar = new JProgressBar();
        JPanel contentPane = new JPanel();
        contentPane.setLayout(new java.awt.BorderLayout());
        contentPane.add(buttonPanel,java.awt.BorderLayout.NORTH);
        contentPane.add(progressBar,java.awt.BorderLayout.CENTER);
        frame.setContentPane(contentPane);
        frame.pack();
        frame.setVisible(true);
    public void actionPerformed(ActionEvent e) {
        if(e.getSource() == newPage) {
            if(currentWorker != null) {
                currentWorker.removePropertyChangeListener(this);
                currentWorker.cancel(true);
            progressBar.setValue(0);
            progressBar.setVisible(true);
            currentWorker = new PageLoader();
            currentWorker.addPropertyChangeListener(this);
            currentWorker.execute();
        }else if(e.getSource() == pageLoaded) {
            if(currentWorker != null) {
                currentWorker.pageLoaded = true;
    public void propertyChange(PropertyChangeEvent evt) {
        if(evt.getPropertyName().equals("progress")) {
            int progress = (Integer) evt.getNewValue();
            progressBar.setValue(progress);
        }else if(evt.getPropertyName().equals("pageLoaded")) {
            progressBar.setVisible(false);
            currentWorker.removePropertyChangeListener(this);
            currentWorker = null;
    private class PageLoader extends SwingWorker<Void,Void> {
        private int progress;
        private boolean pageLoaded;
        public Void doInBackground() {
            for (progress = 0; progress < 100; progress++) {
                if(pageLoaded) break;
                try {
                    Thread.sleep(70);
                } catch (InterruptedException e) {
                    //return gracefully since "New Page" button was pressed
                    return null;
                setProgress(progress);
            /**The progress might have reached 100 naturally. In which case
             * pageLoaded is false and needs to be set to true.*/
            pageLoaded = true;
            /**The Page Loaded button might have been pressed, in which case
             * the progress is not 100 and needs to be set to 100.*/
            progress = 100;
            setProgress(100);
            try{
                //show completed progress bar for 1 second.
                Thread.sleep(1000);
            }catch(InterruptedException e) {
                pageLoaded = false;
                return null;
            return null;
        //executed on EDT when doInBackground() method is done
        public void done() {
            System.out.println("Progress reached: " + progress + "% " +
                    "upon termination.");
            if(pageLoaded) {
               firePropertyChange("pageLoaded",null,null);
    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
               new ProgressBarTest();
}