为什么函数不画重点？

Question

每当我在单击的相同位置单击框架上的鼠标时，我都会尝试在框架上绘制一个点。我编写/复制的代码调用绘图函数，但没有绘制该点，我无法找出问题所在。这是代码：

import static com.sun.java.accessibility.util.AWTEventMonitor.addMouseListener;
import java.awt.image.BufferedImage;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.Random;
public class MyCanvas
{
    JLabel view;
    BufferedImage surface;
    public MyCanvas()
    {
        surface = new BufferedImage(600,400,BufferedImage.TYPE_INT_RGB);
        view = new JLabel(new ImageIcon(surface));
        Graphics g = surface.getGraphics();
        g.setColor(Color.ORANGE);
        g.fillRect(0,0,600,400);
        //g.setColor(Color.BLACK);
        //g.drawLine(10, 20, 350, 380);
        g.dispose();
        /*
        // RANDOM POINTS WORKING
        ActionListener listener = new ActionListener() {
            public void actionPerformed(ActionEvent ae) {
                int x = random.nextInt(600);
                int y = random.nextInt(400);
                addNewElement(x,y);
            }
        };
        Timer timer = new Timer(200, listener);
        timer.start();
        */
    }
    public void addNewElement(int x,int y) {
        Graphics g = surface.getGraphics();
        drawNode(x,y,g);
        g.dispose();
        view.repaint();
    }
    public static void main(String[] args)
    {
        MyCanvas canvas = new MyCanvas();
        JFrame frame = new JFrame();
        int vertexes = 0;
        // Change this next part later to be dynamic.
        vertexes = 10;
        int canvasSize = vertexes * vertexes;
        frame.setSize(canvasSize, canvasSize);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setContentPane(canvas.view);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
        frame.addMouseListener(new MouseAdapter() {
            public void mouseClicked(MouseEvent e) {
                //Restituisco le coordinate del click(x,y)
                System.out.println(e.getPoint());
                //NOT WORKING
                MyCanvas a = new MyCanvas(); 
                a.addNewElement(e.getPoint().x,e.getPoint().y);
            }
        });
    }
    public void drawNode(int x, int y, Graphics g)
    {
            g.setColor(Color.white);
            g.fillOval(x, y, 8, 8);
            g.drawOval(x, y, 8, 8);
    }
}

Answer 1

删除：

  g.dispose();
  view.repaint();

切勿释放不是创建的 GUI 对象。此外，repaint()将在绘制点后删除您的点，因为它调用刷新图像的paint()。您的观点不会刷新，因为它不包含在paint中。另请注意，您在帧上定义鼠标事件，并在view上应用坐标。

Answer 2

好的，我只是想出了问题：我每次点击都会实例化一个新类。为了解决它，我只是改变了

MyCanvas a = new MyCanvas(); 
a.addNewElement(e.getPoint().x,e.getPoint().y);

自

canvas.addNewElement(e.getPoint().x,e.getPoint().y);