无法在Java Swing中从JPanel中删除JComponents

Question

我有一个基本的抽屉应用程序，当我绘制一个新行时，我必须删除最后一行。这是我的代码：

public class DrawLine extends JFrame implements MouseListener {

    private JPanel contentPane;
    private int x0, y0;
    private MyLine ml;
    private JPanel panel;

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    DrawLine frame = new DrawLine();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    public DrawLine() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 450, 300);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        contentPane.setLayout(new BorderLayout(0, 0));
        setContentPane(contentPane);

        panel = new JPanel();
        contentPane.add(panel, BorderLayout.CENTER);

        panel.addMouseListener(this);;


    }

    @Override
    public void mousePressed(MouseEvent e) {

        for (Component c : panel.getComponents()) {
            panel.remove(c);
        }
        x0 = e.getX();
        y0 = e.getY();

    }

    @Override
    public void mouseReleased(MouseEvent e) {


        if(ml == null){
            ml = new MyLine(x0, y0, e.getX(), e.getY());
            panel.add(ml);
        }
        else{

            ml = new MyLine(x0, y0, e.getX(), e.getY());
            ml.paintcomponent(getGraphics());
        }

    }

}

这也是我的Line类：

public class MyLine extends JComponent{
    private int x0, y0, x1, y1;

    public MyLine(int x0, int y0, int x1, int y1){
        this.x0 = x0;
        this.y0 = y0;
        this.x1 = x1;
        this.y1 = y1;
    }

    public void paintcomponent(Graphics gr){
        super.paintComponent(gr);
        gr.drawLine(x0, y0, x1, y1);
    }
}

在mousePressed事件监听器中，我使用for循环，其中所有组件都从面板中删除，但它不起作用。我也尝试使用panel.removeAll（），但没有成功。