How do I call the invokeLater method from a thread in Java?

Question

Ok, this is my problem:

I am trying to build a custom download helper for one of my projects. I wanted my implementation to allow multiple downloads (running simultaneously) so I figured that I should start a thread for every download.

However, the problem is that I also want to update the GUI of my program. To do that, I wanted to use the invokeLater() method since Swing is not thread-safe.

Now: If I use the invokeLater() method inside each thread to update a progressbar, how would a thread know about my GUI? Please let my know what you think about this approach and how you would solve this problem.

Please consider this aswell:

public class frame extends JFrame {
    public frame() {
        //the constructor sets up the JProgressBar and creates a thread object
    }

    public void getFiles() {
        // Here I would start the thread.
        thread.start();
    }
}

And here is another class that sets up the thread:

public class theThread extends Thread {
    // Here I would create the thread with its constructor 

    public void run() {
        // Here comes some code for the file download process
        //
        // While the thread is running the method below gets called.
        updateGUI();
    }

    public void updateGUI() {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                // Here I need to place the code to update the GUI
                // However, this method has no idea of what the GUI looks like
                // since the GUI was setup in the class 'frame'.
            }
        });
    } 
}    

Answer 1

You could have a constructor that takes the frame as a parameter:

public class TheThread extends Thread {
    private final JFrame frame;

    public TheThread(Runnable r, JFrame frame) {
        super(r);
        this.frame = frame;
    }
}

Now you can call frame.doSomething(); from your updateGUI method.

Note that it is generally better practice to implement Runnable than to extend Thread .

Alternatively, you could use SwingWorkers which have been designed to handle situations like what you describe (background thread that updates the UI).