我试着在我的JFrame上看我的时钟，但是它总是在上面写。

import javax.swing.*;
import java.awt.*;
import java.text.SimpleDateFormat;
import java.util.Date;

public class ClockFrame extends JFrame {
    private JLabel clockLabel;

    public ClockFrame() {
        setTitle("时钟");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLayout(new FlowLayout());
        setSize(200, 100);

        clockLabel = new JLabel();
        clockLabel.setFont(new Font("Arial", Font.BOLD, 24));
        clockLabel.setOpaque(false);
        add(clockLabel);

        setVisible(true);

        // 更新时钟显示
        updateClock();
    }

    private void updateClock() {
        Thread clockThread = new Thread(() -> {
            while (true) {
                SimpleDateFormat dateFormat = new SimpleDateFormat("HH:mm:ss");
                String currentTime = dateFormat.format(new Date());
                clockLabel.setText(currentTime);
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
        clockThread.start();
    }

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