在按钮单击时将JLabel转换为计时器

import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Timer;
import java.util.TimerTask;

public class TimerExample {
    public static void main(String[] args) {
        JFrame frame = new JFrame("Timer Example");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(300, 200);

        JLabel timerLabel = new JLabel("00:00:00");
        timerLabel.setHorizontalAlignment(JLabel.CENTER);
        frame.add(timerLabel);

        JButton startButton = new JButton("Start");
        startButton.addActionListener(new ActionListener() {
            Timer timer;
            int seconds = 0;

            @Override
            public void actionPerformed(ActionEvent e) {
                if (timer == null) {
                    timer = new Timer();
                    timer.scheduleAtFixedRate(new TimerTask() {
                        @Override
                        public void run() {
                            seconds++;
                            int hour = seconds / 3600;
                            int minute = (seconds % 3600) / 60;
                            int second = seconds % 60;
                            String time = String.format("%02d:%02d:%02d", hour, minute, second);
                            timerLabel.setText(time);
                        }
                    }, 1000, 1000);
                }
            }
        });
        frame.add(startButton);

        frame.setVisible(true);
    }
}