JPanel有绘图问题

Question

我想要的是我的坐标源和红点之间的动态线。 红点应该留下一丝点，当我重新绘制时，线条不应留下痕迹。

由于我super.paintComponent(gfx)，现在既没有线也没有点留下痕迹。 任何想法我怎样才能实现动态线和跟踪点？ 下面的类是可编译的，因此您可以重建我的问题。

我的主要和JPanel课程是：

import javax.swing.*;
import java.util.ArrayList;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class Main {

    public static void main(String Args[])
    {
        //Initialize Points
        ArrayList<Point> carthCoords = new ArrayList<Point>();
        Point p1 = new Point(300,300);
        Point p2 = new Point(-300,-200);
        carthCoords.add(p1);
        carthCoords.add(p2);

        //Create JPanel
        CoordSystem coordPanel = new CoordSystem(800, 800, carthCoords);

        //Display Points on JFrame
        JFrame jFrame = new JFrame("Points and Vectors");
        jFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        jFrame.setSize(800, 800);
        javax.swing.Timer t = new javax.swing.Timer(10, coordPanel);
        jFrame.add(coordPanel);
        t.start();
        jFrame.setVisible(true);
    }
}

JPanel课程：

import javax.swing.*;
import java.util.ArrayList;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class CoordSystem extends JPanel implements ActionListener{
    public int W;
    public int H;
    ArrayList<Point> points;

    public CoordSystem(int width, int height, ArrayList<Point> pointz) 
    {
        this.W = width;
        this.H = height;
        this.points = pointz;
    }

    public void paintComponent(Graphics gfx)
    {
        super.paintComponent(gfx);
        setBackground(Color.white);
        //Draw Coordinate System
        gfx.setColor(Color.blue);
        gfx.drawLine(W/2, 0, W/2, H);
        gfx.drawLine(0, H/2, W, H/2);

        //Draw Points
        if (points != null)
        {
            int x,y;
            for (Point p : points)
            {
                x = (int)p.getX();
                y = (int)p.getY();
                gfx.setColor(Color.red);
                gfx.fillOval((W/2) + x, (H/2) - y, 10, 10);
                gfx.setColor(Color.black);
                gfx.drawLine(W/2 + x,H/2 - y, W/2, H/2);
            }
        }
    }

    @Override
    public void actionPerformed(ActionEvent actionEvent) {
        for (Point point : points)
        {
            point.translate(0,-1);
        }
        repaint();
    }
}