空指针异常，？ - -#

Question

import java.awt.*;
import javax.swing.*;class Astar extends JPanel {
int[][] map = {
{1,1,0,0,0,0,0,0,0,0},
{1,0,0,0,0,0,0,0,0,0},
{0,0,0,0,0,0,0,0,0,0},
{0,0,0,1,1,1,1,1,0,0},
{0,0,0,0,0,0,0,1,0,0},
{0,0,0,0,0,0,0,1,0,0},
{0,0,0,0,0,0,0,1,0,0},
{1,1,1,0,0,0,0,0,0,0},
{1,0,0,0,0,0,0,0,0,0},
{0,0,0,0,0,0,1,1,0,0},
           };
 Cell[][] map1;
 
 public Astar(){
  map1 = new Cell[10][10];
for(int i=0;i<10;i++)
for(int j=0;j<10;j++)
map1[i][j].value = map[i][j];
  JFrame f = new JFrame();
  f.setBounds(100,100,600,500);
  f.add(this);
  f.setVisible(true);
 } 
public void paintComponent(Graphics g){
for(int i=0;i<10;i++){
for(int j=0;j<10;j++){
if(map[i][j]==0){
g.draw3DRect(40*j,40*i,40,40,true);
g.drawString(map1[i][j].toString1(),40*j,40*i);
}
else if(map[i][j]==1)
g.fill3DRect(40*j,40*i,40,40,true);
}
}
}
public static void main(String args[]){
new Astar();
}
class Cell{
int value;
boolean seen;
boolean open;
int direction;
Cell(){
seen = true;
    open = true;
}
public String toString1(){
if(open)
return "Open";
else return "Closed";
}
}
}

Answer 1

for(int i=0;i<10;i++)
            for(int j=0;j<10;j++)
{
map1[i][j]= new Cell();
map1[i][j].value = map[i][j];
}

Answer 2

虽然map1 = new Cell[10][10];你初始化了一个二维Cell数组，但是你并没有对里面的每个Cell进行初始化，所以默认初始化值为null，用null来调用value，所以就报错了

Answer 3

空指针就是 xx.xx  .前面的那个值为null； 比较好找

Answer 4

    int[][] map = {
                    {1,1,0,0,0,0,0,0,0,0},
                    {1,0,0,0,0,0,0,0,0,0},
                    {0,0,0,0,0,0,0,0,0,0},
                    {0,0,0,1,1,1,1,1,0,0},
                    {0,0,0,0,0,0,0,1,0,0},
                    {0,0,0,0,0,0,0,1,0,0},
                    {0,0,0,0,0,0,0,1,0,0},
                    {1,1,1,0,0,0,0,0,0,0},
                    {1,0,0,0,0,0,0,0,0,0},
                    {0,0,0,0,0,0,1,1,0,0},
               };
这个不报错？神奇

Answer 5

还真不报错，汗～！神奇的java

Answer 6

空指针异常，学Java时老师常常提起，现在都忘得差不多了。

Answer 7

你怎把Cell放在Astar 里面了，应该放到Astar 外面，就好了。