添加方法paint()时，JPanel的背景色将替换为灰色

import javax.swing.*;
import java.awt.*;

public class MyPanel extends JPanel {
    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.setColor(Color.GRAY);
        g.fillRect(0, 0, getWidth(), getHeight());
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame("JPanel Background Color Example");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        MyPanel panel = new MyPanel();
        panel.setPreferredSize(new Dimension(400, 300));

        frame.getContentPane().add(panel);
        frame.pack();
        frame.setVisible(true);
    }
}