小白求助！请问怎么用Graphics类画多边形？？要用drawLine 这个方法！

public class Test extends JPanel {
    /**
     *
     */
    private static final long serialVersionUID = 1L;
    static class Cell {
        int x;
        int y;
        public int getX() {
            return x;
        }
        public int getY() {
            return y;
        }
        public Cell(int x, int y) {
            super();
            this.x = x;
            this.y = y;
        }
    }
    private static List<Cell> cells = new ArrayList<>();
    @Override
    public void paint(Graphics g) {
        g.setColor(Color.RED);
        int[] xPoints = new int[cells.size()];
        int[] yPoints = new int[cells.size()];
        for (int i = 0; i < cells.size(); i++) {
            xPoints[i] = cells.get(i).getX();
            yPoints[i] = cells.get(i).getY();
        }
        g.fillPolygon(xPoints, yPoints, cells.size());
        if(cells.size() < 1) {
            g.setColor(Color.WHITE);
            g.fillRect(0, 0, 400, 400);
        }
    }
    static LocalDateTime prevClickTime = LocalDateTime.now();
    static LocalDateTime curClickTime = null;
   
    MouseAdapter mouseAdapter = new MouseAdapter() {
        
        public void mouseClicked(MouseEvent e) {
            Test.this.repaint();
            curClickTime = LocalDateTime.now();
            cells.add(new Cell(e.getX()-8, e.getY()-30));
            Duration duration = Duration.between(prevClickTime, curClickTime);
            int nano = duration.getNano();
            if(nano <= Duration.ofMillis(180).getNano()) {
                System.out.println("clear");
                cells.clear();
            }
            prevClickTime = curClickTime;
        };
    };
    private void start() {
        JFrame jframe = new JFrame();
        jframe.setVisible(true);
        jframe.setSize(400, 400);
        jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        jframe.add(this);
        jframe.addMouseListener(mouseAdapter);
    }
    public static void main(String[] args) {
        new Test().start();
    }
}