单击按钮时将 JLabel 转换为计时器

Question

Within my application, I am creating a timerLabel and timerPanel as follows:

// Add timer panel
JPanel timerPanel = new JPanel();
timerPanel.setBorder(new EmptyBorder(0, 0, 0, 0));
timerPanel.setBackground(new Color(0x757575));
c.gridx = 0;
c.fill = GridBagConstraints.HORIZONTAL;
c.insets = new Insets(0,0,0,20);
c.gridy = 0;
centerPanel.add(timerPanel, c);

// Add timer label
JLabel timerLabel = new JLabel("00:00", SwingConstants.RIGHT);
timerLabel.setForeground(Color.black);
timerLabel.setFont(new Font("Serif", Font.BOLD, 30));
timerLabel.setHorizontalAlignment(JLabel.RIGHT);
c.gridx = 1;
c.fill = GridBagConstraints.HORIZONTAL;
c.gridy = 0;
timerLabel.setForeground(Color.white);
timerPanel.add(timerLabel, c);

I would like for the timer to start counting down from 60 seconds whenever the user clicks on the Start, and restarted the button. Below is the ActionListener I have implemented. Right now I am unsure about how to do this:

  private class ButtonHandler implements ActionListener {
    @Override
    public void actionPerformed(java.awt.event.ActionEvent e) {

      // The text from the button that the user clicked.
      String cmd = e.getActionCommand();

      // Respond to Quit button by ending the program.
      if (cmd.equals(GuiText.START.toString())) {
        startGame();
        // start the timer here
      } else if (cmd.equals(GuiText.PREVIOUS.toString())) {
        QuestionList.selectRandomQuestion();
        questionLabel.setText(message);
        // reset the timer here
      } else if (cmd.equals(GuiText.NEXT.toString())) {
        QuestionList.selectRandomQuestion();
        questionLabel.setText(message);
        // reset the timer here
      } else {
        textArea.setText(cmd);
      }
      // Causes the display to be redrawn, to show any changes made.
      display.repaint();
    }
  }

Lastly I need a way of tracking when the timer gets to zero and "doing something" when it does beign able to call a method? How can I accomplish this? My full code is available here (for context): https://pastebin.com/44XWxTQt . I appreciate your time and help.

Answer 1

Anything involving updating Swing components should revolve around javax.swing.Timer . This has start() / stop() methods to call on your button-clicks. It is also configurable via the constructor to call its own actionPerformed method every second (so you can update the JLabel and repaint).

https://docs.oracle.com/javase/tutorial/uiswing/misc/timer.html