JProgressbar not showing (without threads)

i have a program that takes some time creating pdf files i would like to show progress to user

when i finish making a pdf file i try to call the progressbar to update its status:

ProgressDialog progress = new ProgressDialog(instance, numberOfInvoices);
progress.setVisible(true);
progress.setAlwaysOnTop(true);

for(int i = 0 ; i<numOfPdfs ; i++){
    progress.change(i + 1);
}

the progressdialog looks like this:

public class ProgressDialog extends JDialog {

    private JProgressBar progressBar;

    public ProgressDialog(Window parent, int aantal) {
        super(parent);

        this.setPreferredSize(new Dimension(300, 150));

        progressBar = new JProgressBar(0, aantal);
        progressBar.setValue(0);
        progressBar.setSize(new Dimension(280, 130));
        this.add(progressBar, BorderLayout.CENTER);

        this.pack();
        this.setLocationRelativeTo(parent);
    }

    public void change(int aantal) {
        if (aantal < progressBar.getMaximum() && aantal >= 0) {
            progressBar.setValue(aantal);
        }
    }
}

all i get is an empty window (white)

i looked around on this forum but the treads solution seems soo complex

between calculation of 2 pdf files i should be able to update the gui, right?

ok colin

i tried this: (complete class)

public class ProgressDialog extends 开发者_运维技巧JDialog {

    private JProgressBar progressBar;
    private String message;
    private static int number;

    public ProgressDialog(Window parent, int max, String message) {
    super(parent);

    this.message = message;
    this.setPreferredSize(new Dimension(300, 150));

    progressBar = new JProgressBar(0, max);
    progressBar.setValue(0);
    progressBar.setSize(new Dimension(280, 130));
    progressBar.setString(message + " 0/" + progressBar.getMaximum());
    progressBar.setStringPainted(true);
    this.add(progressBar, BorderLayout.CENTER);

    this.pack();
    this.setLocationRelativeTo(parent);

    setCursor(Cursor.getPredefinedCursor(Cursor.WAIT_CURSOR));


    }

    public void change(int number) {
    ProgressDialog.number = number;
    SwingUtilities.invokeLater(new Runnable() {

        public void run() {
        int number = ProgressDialog.getAantal();
        if (number < progressBar.getMaximum() && number >= 0) {
            progressBar.getModel().setValue(number);
            progressBar.setString(message + " " + progressBar.getValue() + "/" + progressBar.getMaximum());
            System.out.println("progressbar update: " + number + "/" + progressBar.getMaximum());
        } else {
            setCursor(null);
            System.out.println("progressbar terminated");
        }
        }
    });
    }

    public static int getAantal(){
    return number;
    }
}

now it still shows the empty window but when all pdf's are ready it does show the progressbar with 0% completed then it closes (like it should do)

any idea why it stays blank during process?

You do need to do it with threads. Better learn it than escape, because it's a common GUI framework design.

It can be as simple as:

public void change(int aantal) {
    SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            if (aantal < progressBar.getMaximum() && aantal >= 0) {
                progressBar.setValue(aantal);
            }
        }
    });
}

Or replace invokeLater() with invokeAndWait().

Read the section from the Swing tutorial on Concurrency to understand why Threads are needed for this problem. Also read the section on "How to Use Progress Bars" for a working example.