Swing Timer stopwatch in Java

Question

Can someone provide me an example of a Swing Timer stopwatch GUI in Java using a constantly-updating JLabel? I am not familiar with using @Override, so please don\'t sugges

Answer 1

I did Google for it, but I wasn't understanding the code that I found

Then you have a bigger problem. How do you expect any of us to provide you with an example you can understand?

A stop watch is conceptually pretty simple, it's simply the amount of time that has passed since it was started. Problems arise when you want to be able to pause the timer, as you need to take into account the amount of time the timer has been running plus the time since it was last started/resumed.

Another issue is, most timers only guarantee a minimum amount of time, so they are imprecise. This means you can't just keep adding the amount of the timer's delay to some variable, you'll eventually end up with a drifting value (inaccurate)

This is a very simple example, all it does is provides a start and stop button. Each time the stop watch is started, it starts from 0 again.

import java.awt.EventQueue;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.time.Duration;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class SimpleStopWatch {

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

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

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new StopWatchPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class StopWatchPane extends JPanel {

        private JLabel label;
        private long lastTickTime;
        private Timer timer;

        public StopWatchPane() {
            setLayout(new GridBagLayout());
            label = new JLabel(String.format("%04d:%02d:%02d.%03d", 0, 0, 0, 0));

            timer = new Timer(100, new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    long runningTime = System.currentTimeMillis() - lastTickTime;
                    Duration duration = Duration.ofMillis(runningTime);
                    long hours = duration.toHours();
                    duration = duration.minusHours(hours);
                    long minutes = duration.toMinutes();
                    duration = duration.minusMinutes(minutes);
                    long millis = duration.toMillis();
                    long seconds = millis / 1000;
                    millis -= (seconds * 1000);
                    label.setText(String.format("%04d:%02d:%02d.%03d", hours, minutes, seconds, millis));
                }
            });

            GridBagConstraints gbc = new GridBagConstraints();
            gbc.gridx = 0;
            gbc.gridy = 0;
            gbc.weightx = 1;
            gbc.gridwidth = GridBagConstraints.REMAINDER;
            gbc.insets = new Insets(4, 4, 4, 4);
            add(label, gbc);

            JButton start = new JButton("Start");
            start.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    if (!timer.isRunning()) {
                        lastTickTime = System.currentTimeMillis();
                        timer.start();
                    }
                }
            });
            JButton stop = new JButton("Stop");
            stop.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    timer.stop();
                }
            });

            gbc.gridx = 0;
            gbc.gridy++;
            gbc.weightx = 0;
            gbc.gridwidth = 1;
            add(start, gbc);
            gbc.gridx++;
            add(stop, gbc);
        }

    }

}

Adding a pause feature isn't hard, it would simply require one additional variable, but I'll leave that up to you to figure out.