Java Swing -如何在画布中绘制新的线条并将其添加到现有线条中？

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

public class LinePanel extends JPanel {
    private java.util.List<Line> lines; // 存储线条的集合

    public LinePanel() {
        lines = new java.util.ArrayList<>();
    }

    public void addLine(Line line) {
        lines.add(line);
        repaint(); // 重绘面板
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        for (Line line : lines) {
            g.drawLine(line.getStartX(), line.getStartY(), line.getEndX(), line.getEndY());
        }
    }
}

public class Line {
    private int startX;
    private int startY;
    private int endX;
    private int endY;

    public Line(int startX, int startY, int endX, int endY) {
        this.startX = startX;
        this.startY = startY;
        this.endX = endX;
        this.endY = endY;
    }

    // 省略getter和setter方法
}

import javax.swing.*;

public class MainFrame extends JFrame {
    public MainFrame() {
        LinePanel linePanel = new LinePanel();
        add(linePanel);

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(400, 400);
        setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> new MainFrame());
    }
}

Line line = new Line(startX, startY, endX, endY);
linePanel.addLine(line);