Question

When a user clicks a button, a long task of approximately 10 seconds will run. During this time I want to show a progress bar to the user. But the main thread has to wait for the worker thread to finish because the worker thread will set a variable that the main thread will use. If I don’t wait the worker thread I will get a NullPointerException when using the variable. So after the worker thread finishes, I will also close the progress bar dialog.

When I wait for the worker thread using join() the progress bar dialog shows (interestingly without the progress bar though) and hangs there.

Thread runnable = new Thread() {

    public void run() {
        try {
            System.out.println("thread basladi");
            threadAddSlaveReturnMessage = request.addSlave(
                ipField.getText(), passField.getText(), 
                nicknameField.getText());
            System.out.println("thread bitti");

        } catch (LMCTagNotFoundException e) {
            e.printStackTrace();
        }

    }
};

Thread runnable_progress = new Thread() {

    public void run() {

        JTextArea msgLabel;
        JDialog dialog;
        JProgressBar progressBar;
        final int MAXIMUM = 100;
        JPanel panel;

        progressBar = new JProgressBar(0, MAXIMUM);
        progressBar.setIndeterminate(true);
        msgLabel = new JTextArea("deneme");
        msgLabel.setEditable(false);


        panel = new JPanel(new BorderLayout(5, 5));
        panel.add(msgLabel, BorderLayout.PAGE_START);
        panel.add(progressBar, BorderLayout.CENTER);
        panel.setBorder(BorderFactory.createEmptyBorder(11, 11, 11, 11));

        dialog = new JDialog(Frame.getFrames()[0], "baslik", true);
        dialog.getContentPane().add(panel);
        dialog.setResizable(false);
        dialog.pack();
        dialog.setSize(500, dialog.getHeight());
        dialog.setLocationRelativeTo(null);
        dialog.setDefaultCloseOperation(JDialog.DO_NOTHING_ON_CLOSE);
        dialog.setAlwaysOnTop(false);
        dialog.setVisible(true);
        msgLabel.setBackground(panel.getBackground());
    }
};

runnable.start();
System.out.println("runnable start");
runnable_progress.start();
System.out.println("progress start");
runnable.join();
System.out.println("runnable join");
runnable_progress.join();
System.out.println("progress join");


if (threadAddSlaveReturnMessage.equalsIgnoreCase("OK")) {
    fillInventoryTable(inventoryTable);
    JOptionPane.showMessageDialog(this, messages.getString("centrum.addslavepanel.SUCCESS"), null, JOptionPane.INFORMATION_MESSAGE);
}

“progress join”

doesn’t get printed.

Answer 1

1. you have the issue with Concurency is Swing, your GUI is visible after all thread are done

2. is possible to moving with JProgressBar (I’m talking about you code) but you have to

   • create and show JDialog, create once time and reuse this container

   • then to start Thread,

   • better could be from Runnable#Thread

   • output to the Swing GUI must be wrapped into invokeLater()

3. this is exactly job for using SwingWorker and with PropertyChangeListener