Java GUI is frozen but program still running in the terminal

Question

I'm trying to make a simple Java GUI chronometer, but whenever I press the start button the GUI freezes and won't allow me to click the stop button, but the program continues to run perfectly on the terminal.

Here is the code of my start button:

startButton = new JButton();
startButton.setText("START");
startButton.setFont(new Font("RuneScape UF", Font.PLAIN, 16));
startButton.setFocusable(false);
startButton.addActionListener(new ActionListener() {
 @Override
 public void actionPerformed(ActionEvent e) {
 if (e.getSource() == startButton) {
 System.out.println("Start button pressed!");
 isRunning = true;
 System.out.println(isRunning);
 long startTime = System.currentTimeMillis();
 while (isRunning) {
 try {
 TimeUnit.SECONDS.sleep(1);
 } catch (InterruptedException interruptedException) {
 interruptedException.printStackTrace();
 }
 long elapsedTime = System.currentTimeMillis() - startTime;
 long elapsedSeconds = elapsedTime / 1000;
 if (elapsedSeconds == 60) {
 elapsedSeconds = 0;
 startTime = System.currentTimeMillis();
 }
 if ((elapsedSeconds % 60) == 0) {
 minutesDisplay++;
 }
 if ((minutesDisplay % 60) == 0 && stupidFix > 0) {
 stupidFix++;
 hoursDisplay++;
 }
 //System.out.println(elapsedSeconds);
 String h = String.format("%02d", hoursDisplay);
 String m = String.format("%02d", minutesDisplay);
 String s = String.format("%02d", elapsedSeconds);
 timePassed.setText(h + ":" + m + ":" + s);
 System.out.println(h + ":" + m + ":" + s);
 }
 }
 }
});

• Lino: That is because the UI thread is stuck in your while (isRunning) loop, you'd have to execute that code in a separate thread
• Anastasia Drozhzha: Maybe this will be helpful: docs.oracle.com/javase/tutorial/uiswing/concurrency/…

Answer 1

You are using a while loop inside a button action listener. Using a while loop inside a button action listener is considered a heavy task.You have to use SwingWorker for this.

You can see the tutorial for it here:

https://docs.oracle.com/javase/7/docs/api/javax/swing/SwingWorker.html

• Andrew Thompson: " Using a while loop inside a button action listener is considered a heavy task." It's only the Thread.sleep(..) that will will block the EDT, so is not necessarily a 'heavy' task. In fact, this is better done by establishing a Swing Timer to update the time. Both situations are covered in the link provided by Anastasia.