Question

I want to show how merge sort perform visually using JFrame. What I want to do is to make visible subsequent JLabel with some time delay. I tried many way but all of them appears at same moment with no intermediate delay.

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
        // TODO add your handling code here:
       // jLabel1.setVisible(false);
        jLabel2.setVisible(false);
        jLabel3.setVisible(false);
        jLabel4.setVisible(false);
        jLabel5.setVisible(false);
        jLabel6.setVisible(false);
        jLabel7.setVisible(false);
        final Timer t=new Timer((4000), null);
         final int delay=2000;
        final ActionListener taskPerformer = new ActionListener() {
      public void actionPerformed(ActionEvent evt) {

          jLabel1.setVisible(true);
          t.getDelay();

          jLabel2.setVisible(true);
          t.setDelay(3000);

          jLabel3.setVisible(true);
          t.setDelay(2000);

          jLabel4.setVisible(true);
          t.setDelay(2000);

          jLabel5.setVisible(true);
          t.setDelay(2000);

          jLabel6.setVisible(true);
          t.setDelay(2000);
                }
  };

  new Timer(delay, taskPerformer).start();

But when I click button all the lables appear at same momenet though I have kept delay.

Answer 1

There are a number of reasons why this won’t work. Firstly, javax.swing.Timer doesn’t work this way. It waits in the background until the given delay has past and then calls the registered ActionListeners actionPerformed method.

Secondly, if it did work this way, it would block the Event Dispatching Thread, preventing it from processing repaint requests.

I think you will find How to use Swing Timers of use.

public class BlinkOut {

    public static void main(String[] args) {
        new BlinkOut();
    }

    public BlinkOut() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Test");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }

        });
    }

    public class TestPane extends JPanel {

        private JLabel[] labels;
        private int[] delays;
        private Timer timer;
        private int index;

        public TestPane() {
            setLayout(new GridLayout(0, 1));
            labels = new JLabel[7];
            for (int index = 0; index < 7; index++) {
                labels[index] = new JLabel("Label " + (index + 1));
                add(labels[index]);
            }
            delays = new int[] {2000, 3000, 2000, 2000, 2000, 2000, 2000};
            JButton hide = new JButton("Hide");
            add(hide);
            hide.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    System.out.println("Click");
                    index = 0;
                    labels[index].setVisible(false);
                    timer.setDelay(delays[index]);
                    timer.start();
                }
            });
            timer = new Timer(delays[0], new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    System.out.println("Tick");
                    timer.stop();
                    index++;
                    if (index < 7) {
                        labels[index].setVisible(false);
                        timer.setDelay(delays[index]);
                        timer.start();
                    }
                }
            });
            timer.setRepeats(false);
            timer.setCoalesce(true);
        }
    }

}