关于JPanel的加载问题；

import java.awt.Container;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import import javax.imageio.ImageIO;
import javax.swing.*;

public class Maze extends JFrame {
   
    public Maze(){
        setSize(510,550);
        setDefaultCloseOperation(3);
        Container cont = this.getContentPane();
        MapImage map = new MapImage();
        add(map);
        


        
        setVisible(true);
    }
   
    public static void main(String[] args) {
        new Maze();
    }
}

class MapImage extends JPanel{
   
    private BufferedImage wall;
    private int[][] map = new int[][]{
        {2,1,1,1,1,1,1,1,1,1},
        {0,0,0,0,0,0,0,0,0,1},
        {1,1,1,1,1,1,1,1,0,1},
        {1,0,0,0,0,0,1,1,0,1},
        {1,0,1,0,1,1,1,1,0,1},
        {1,0,1,0,0,0,0,0,0,1},
        {1,0,1,1,1,1,1,1,1,1},
        {1,0,0,0,0,0,0,0,0,1},
        {1,1,1,1,1,1,1,1,0,3},
        {1,1,1,1,1,1,1,1,1,1}};
        
    public void paint(Graphics g){
        try {
            //注意下面的导入方式；很有用；在程序移植过程中，通过相对路径可以保证资源的正常加载
                wall= ImageIO.read(this.getClass().getResource("/Material/brick.png"));
                for(int i = 0;i<10;i++){
                    for(int j=0;j<10;j++){
                        if(this.map[i][j]==1){
                            g.drawImage(wall,51*i,51*j,null);
                        }
                    }
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
    }
}