how to display loading dialog at center of app screen?

I want to know how to display loading dialog at cent开发者_Python百科er of app screen. An indefinite progress bar.

If you're talking about a JDialog, after calling pack() on it, call setLocationRelativeTo(null) to center it.

Here's how I typically show a "loading..." progress bar. The loading itself must happen on a background thread to make sure the progress bar keeps updating. The frame with the progress bar will be shown in the center of the screen.

public static void main(String[] args) throws Throwable {

    final JFrame frame = new JFrame("Loading...");
    final JProgressBar progressBar = new JProgressBar();
    progressBar.setIndeterminate(true);
    final JPanel contentPane = new JPanel();
    contentPane.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));
    contentPane.setLayout(new BorderLayout());
    contentPane.add(new JLabel("Loading..."), BorderLayout.NORTH);
    contentPane.add(progressBar, BorderLayout.CENTER);
    frame.setContentPane(contentPane);
    frame.pack();
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);


    Runnable runnable = new Runnable() {
        public void run() {
            // do loading stuff in here
            // for now, simulate loading task with Thread.sleep(...)
            try {
                System.out.println("Doing loading in background step 1");
                Thread.sleep(1000);
                System.out.println("Doing loading in background step 2");
                Thread.sleep(1000);
                System.out.println("Doing loading in background step 3");
                Thread.sleep(1000);
                System.out.println("Doing loading in background step 4");
                Thread.sleep(1000);
                System.out.println("Doing loading in background step 5");
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            // when loading is finished, make frame disappear
            SwingUtilities.invokeLater(new Runnable() {
                public void run() {
                    frame.setVisible(false);
                }
            });

        }
    };
    new Thread(runnable).start();
}

display loading dialog at center of app screen.

dialog.setLocationRelativeTo(...);

An indefinite progress bar.

Read the section from the Swing tutorial on How to Use Progress Bars

From the documentation:

JProgressBar progressBar = new JProgressBar();
progressBar.setIndeterminate(true);

This will create the progress bar. To center it, you should take a look at the different kinds of layout managers in java. Without any examples of your existing code, it's hard to give a more precise answer to your question.