如何将画布从另一个类添加到JFrame？

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

class MyCanvas extends JPanel {
    private Canvas canvas;

    public MyCanvas() {
        canvas = new Canvas();
        canvas.setSize(400, 400);
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        // 在这里实现画布的绘制逻辑
        g.setColor(Color.RED);
        g.fillRect(0, 0, 400, 400);
    }

    public Canvas getCanvas() {
        return canvas;
    }
}

public class MainFrame extends JFrame {
    private Canvas canvas;

    public MainFrame() {
        setTitle("My Frame");
        setSize(500, 500);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        MyCanvas myCanvas = new MyCanvas();
        canvas = myCanvas.getCanvas();
        add(myCanvas);
    }

    public Canvas getCanvas() {
        return canvas;
    }

    public static void main(String[] args) {
        MainFrame frame = new MainFrame();
        frame.setVisible(true);
    }
}