instruction apparently not executed

On clicking my test button, I should see "first message" displayed, then, after a 3 second delay, "second message" displayed. Here's my code:

Code:

---

    private class TestButtonWatcher implements ActionListener
    {
        public void actionPerformed(ActionEvent a)
        {
          messagesBox.setText("first message");
          delay(3000);
          messagesBox.setText("second message");
        }
    }

    private void delay(int interval)
    {
      try {Thread.sleep(interval);}
      catch(InterruptedException e) {System.exit(0);}
    }

---

BUT: on clicking, "first message" is NOT displayed; there is a 3 second delay and then "second message" IS displayed.

Any help appreciated; thanks.

First message actually is displayed, but only after 3 sec have elapsed and only for a fraction of a second only.

Never call Thread.sleep on the EDT, Swing's main thread -- it simply puts the whole GUI to sleep. If you need a delay, use a Swing Timer.

Very grateful; thanks.
What does "EDT" mean?

Quote:

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Originally Posted by rippon

Very grateful; thanks.
What does "EDT" mean?

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Event Dispatch Thread

see: Concurrency in Swing

A short example with a Swing Timer:

Code:

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import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.*;

public class ShowDelay {

  public static void main(String[] args) {
      final JLabel messageLabel = new JLabel(" ");
      JButton testBtn = new JButton("Test");
      testBtn.addActionListener(new ActionListener() {
       
        // button's action listener
        public void actionPerformed(ActionEvent e) {
            messageLabel.setText("first message");
           
            // timer, which has it's own ActionListener
            new Timer(3000, new ActionListener() {
              public void actionPerformed(ActionEvent e) {
                  messageLabel.setText("second message");
                  ((Timer)e.getSource()).stop(); // turn timer off
              }
            }).start(); // start Timer
        }
      });
     
      JPanel panel = new JPanel(new BorderLayout());
      panel.add(messageLabel, BorderLayout.NORTH);
      panel.add(testBtn, BorderLayout.CENTER);

      JFrame frame = new JFrame("ShowDelay");
      frame.getContentPane().add(panel);
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
  }
}

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