关于在JFrame上单击鼠标时添加矩形

import javax.swing.*;
import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

public class RectangleFrame extends JFrame {
    private JPanel panel;

    public RectangleFrame() {
        panel = new RectanglePanel();
        add(panel);

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(500, 500);
        setVisible(true);
    }

    private class RectanglePanel extends JPanel {
        private int x, y, width, height;

        public RectanglePanel() {
            addMouseListener(new MouseAdapter() {
                @Override
                public void mouseClicked(MouseEvent e) {
                    x = e.getX();
                    y = e.getY();
                    width = 100;
                    height = 100;
                    repaint();
                }
            });
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            g.drawRect(x, y, width, height);
        }
    }

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