倒数计时器，在 JLabel 中显示秒数时出错

Question

I am having trouble in displaying the seconds into a label. Whenever i run the code, it should be "9 (minutes):59 (seconds)" but it don't go as planned instead it only show 9 minutes.

Note: I just used one label to display the minutes-seconds timer.

Here is the code: I used method.

private void countDown() {
        tmClock = new Timer();
        NumberFormat nbFormat = new DecimalFormat("00");
         if (minutes == 0 && seconds == 0) {
           JOptionPane.showMessageDialog(null, "time's up!");
           tmClock.cancel();
           new Result().setVisible(true);
           this.dispose();
        } else if (seconds == 0) {
           minutes--;
           seconds = 59;
        }
         lblTime.setText(nbFormat.format(minutes) + ":" );
            String format = nbFormat.format(seconds);
        tmClock.schedule(new TimerTask() {
            @Override
            public void run() {
                seconds--;
                countDown();
            }
        }, 1000);

    }

Answer 1

Many problems here:

• You're using the wrong Timer class. This is a Swing application and the thread-safe way to do this is to use javax.swing.Timer , not java.util.Timer
• You're calling countDown() within your TimerTask, and almost in a recursive fashion adding new TimerTasks incorrectly to the Timer object. Note that you shouldn't even be using java.util.TimerTask since again, this is a Swing application.

Solution:

• Use a Swing Timer instead.
• In the Timer's ActionListener, update your seconds value and then set the JLabel's text.

eg,

// declaration section, create the Swing Timer
private int timerDelay = 1000; // msecs
private Timer myTimer = new Timer(timerDelay, e -> countDown());

// perhaps in a constructor or button's ActionListener, start the Timer
myTimer.start();

private void countDown() {
    // seconds--; // update seconds
    if (minutes == 0 && seconds == 0) {
        myTimer.stop(); // stop the Timer if time's up
        JOptionPane.showMessageDialog(null, "time's up!");
        new Result().setVisible(true);
        this.dispose();
    } else if (seconds == 0) {
        minutes--;
        seconds = 59;
    } else {
        seconds--;
    }

    // create label's text and update JLabel
    String text = String.format("%02d:%02d", minutes, seconds);
    lblTime.setText(text);
}

Working example:

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

import javax.swing.*;

@SuppressWarnings("serial")
public class TestTimer extends JPanel {
    private static final String FORMAT_TXT = "%02d:%02d";
    private int seconds = 0;
    private int minutes = 10;
    private JLabel lblTime = new JLabel(String.format(FORMAT_TXT, minutes, seconds));
    private int timerDelay = 1000; // msecs
    private Timer myTimer = new Timer(timerDelay, e -> countDown());

    public TestTimer() {
        lblTime.setHorizontalAlignment(SwingConstants.CENTER);
        setLayout(new BorderLayout());
        add(lblTime, BorderLayout.PAGE_START);
        add(new JButton(new AbstractAction("Start") {

            @Override
            public void actionPerformed(ActionEvent e) {
                if (myTimer != null && !myTimer.isRunning()) {
                    myTimer.start();                    
                }
            }
        }));
    }

    private void countDown() {
        if (minutes == 0 && seconds == 0) {
            if (myTimer != null && myTimer.isRunning()) {
                myTimer.stop(); // stop the Timer if time's up
            }
            JOptionPane.showMessageDialog(this, "time's up!");
            // new Result().setVisible(true);
            // this.dispose();
        } else if (seconds == 0) {
            minutes--;
            seconds = 59;
        } else {
            seconds--; // update seconds
        }
        // create label's text and update JLabel
        String text = String.format("%02d:%02d", minutes, seconds);
        lblTime.setText(text);
    }

    private static void createAndShowGui() {
        TestTimer mainPanel = new TestTimer();

        JFrame frame = new JFrame("Test Timer");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> createAndShowGui());
    }
}