setText() not working in mouseClicked() function

Question

 public class Pragrassbar extends JFrame implements MouseListener {

    JProgressBar jb;
    int i = 0, num = 0;
    JButton jbt;
    JLabel jl;

    Pragrassbar() {
        setSize(400, 400);

        setLayout(new FlowLayout());
        jbt = new JButton("Start");
        jl = new JLabel("Click Start!");

        jb = new JProgressBar(0, 2000);
        jb.setValue(0);
        jb.setStringPainted(true);
        jbt.addMouseListener(this);
        add(jbt);
        add(jb);
        add(jl);

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public void mouseClicked(MouseEvent me) {

        jl.setText("downloading.....");

        jbt.setEnabled(false);

        try {

            while (i <= 2000) {

                jb.setValue(i);
                jb.paintImmediately(0, 0, 200, 25);
                i = i + 40;

                Thread.sleep(30);

            }
            jl.setText("download complete");
            jbt.setEnabled(true);
        } catch (Exception ex) {
            ex.printStackTrace();
        }

    }

    public static void main(String[] args) throws Exception {
        Pragrassbar m = new Pragrassbar();
        m.setVisible(true);

    }

setText() not functioning under mouseClicked function of MouseListener interface although it works after the while loop that i have used

Answer 1

The Thread.sleep() causes the Event Dispatch Thread (EDT) to sleep which means the GUI can't repaint itself until the looping code is finished executing.

Don't use Thread.sleep. Instead long running code should execute in a separate Thread so you don't block the EDT. You should probably use a SwingWorker for this.

Read the section from the Swing tutorial on Concurrency for more information and working examples on this approach.

You can also read the section on How to Use Progress Bars for the proper way to do this.