Question

I want to change a progress bar use SetValue(int),but it doesn’t work,it always change directly from 0 to 100 when progress finish.I try to create a new thread to invoke “setValue(int)”,instead of invoking form UI thread,but it’s still not worked.

my code:

public class UpdateProgressBar extends Thread{
public UpdateProgressBar(javax.swing.JProgressBar progressBar){
    this.progressBar = progressBar;
}
public void update(){
    for(int i = 1; i <= 100; i++){
         progressBar.setValue(i);
        try {
            sleep(10);
        } catch (InterruptedException ex) {
            Logger.getLogger(UpdateProgressBar.class.getName()).log(Level.SEVERE, null, ex);
        }
    }         
}   
private javax.swing.JProgressBar progressBar;
}

,progressBar is defined in UI thread,then I UpdateProgressBar upb = new UpdateProgressBar(progressBar); in UI thread and invoke it’s update wayupb.update();did I make some mistake?

Answer 1

Although you have declared UpdateProgressBar to extend Thread you are not actually running it as a separate thread. You need to call start() to make the new thread actually run. If you call upb.update() from the event dispatch thread then you are executing that method on the event dispatch thread.

You want this in your client code:

UpdateProgressBar upb = new UpdateProgressBar(progressBar);
upb.start();

and change your UpdateProgressBar class to this:

public class UpdateProgressBar extends Thread{
    public UpdateProgressBar(javax.swing.JProgressBar progressBar){
        this.progressBar = progressBar;
    }

    @Override
    public void run(){
        for(int i = 1; i <= 100; i++) {
            final int j = i;
            SwingUtilities.invokeLater(new Runnable() {
                public void run() {
                    progressBar.setValue(j);
                }
            });
            try {
                sleep(10);
            } catch (InterruptedException ex) {
                Logger.getLogger(UpdateProgressBar.class.getName()).log(Level.SEVERE, null, ex);
            }
        }
    }
    private javax.swing.JProgressBar progressBar;
}

You need to have the SwingUtilities.invokeLater because Swing components are not thread-safe. You also need the nasty final int j = i because of Java’s less-than-brilliant handling of closures. Putting your code into the run method means it will be executed when you call Thread.start().