Question

我有一个典型的NullPointerException：

Exception in thread "Thread-0" java.lang.NullPointerException
at com.game.main.SpriteSheet.grabImage(SpriteSheet.java:17)
at com.game.main.Textures.getTextures(Textures.java:30)
at com.game.main.Textures.<init>(Textures.java:21)
at com.game.main.Game.init(Game.java:80)
at com.game.main.Game.run(Game.java:116)
at java.lang.Thread.run(Thread.java:745)

并且我非常确定我知道null的位置，我认为这是这个方法（这也就是getImage方法在我创建的spritesheet.png图像中加载你想要的任何网格）

public BufferedImage grabImage(int column, int row, int width, int height){
        System.out.println("img is " + image); //<<<< How I tested for null.. May not be the best way, but image said to be null

        BufferedImage img = image.getSubimage((column * 32) - 32, (row * 32) - 32, width, height);

        return img;

}

我已经看过这个类中的所有内容，这是类：SpiteSheet.class

package com.game.main;

import java.awt.image.BufferedImage;

public class SpriteSheet {

private BufferedImage image;

public SpriteSheet(BufferedImage image){
    this.image = image;
    System.out.println("img is " + this.image); // <<<<<<<<< THIS ONE SHOWS "img is nullException in thread "Thread-0" " in the console
}

public BufferedImage grabImage(int column, int row, int width, int height){
    System.out.println("img is " + image); //<<<< How I tested for null.. May not be the best way, but image said to be null

    BufferedImage img = image.getSubimage((column * 32) - 32, (row * 32) - 32, width, height);

    return img; 
}
}

我想知道我怎么能启动它？虽然我猜测它已经是image.getSubimage（代码），但我测试了this.image，它说，那就是NullPointerException ...但它应该已经启动了。

可能涉及的更多课程

Textures.class

  package com.game.main;

  import java.awt.image.BufferedImage;

  public class Textures {

    public BufferedImage[] player = new BufferedImage[3];
    public BufferedImage[] missile = new BufferedImage[3];
    public BufferedImage[] enemy = new BufferedImage[3];



    private SpriteSheet ss;
    private Game game;

    public Textures(Game game){
        this.game = game;
        ss = new SpriteSheet(game.getSpriteSheet());

        getTextures(); // This is line 21


    }

    public void getTextures(){



    player[0] = ss.grabImage(1, 1, 32, 32); //This is line 30
    player[1] = ss.grabImage(1, 2, 32, 32);
    player[2] = ss.grabImage(1, 3, 32, 32);

    missile[0] = ss.grabImage(2, 1, 32, 32);
    missile[1] = ss.grabImage(2, 2, 32, 32);
    missile[2] = ss.grabImage(2, 3, 32, 32);

    enemy[0] = ss.grabImage(3, 1, 32, 32);
    enemy[1] = ss.grabImage(3, 2, 32, 32);
    enemy[2] = ss.grabImage(3, 3, 32, 32);


}

}

game.class非常大，所以我会给出它所涉及的主要方法（得到它？init（），在其中...）

Game.class

 public void init(){

requestFocus(); //Brings focus to the screen at the start
BufferedImageLoader loader = new BufferedImageLoader();
try{

    spriteSheet = loader.loadImage("/Sprite_Sheet.png");
    background = loader.loadImage("/Background.png");

}catch(IOException e){
    e.printStackTrace();
}

addKeyListener(new KeyInput(this));

tex = new Textures(this);
p = new Player(300,300, tex);
c = new Controller(tex);

ea = c.getEntityA();
eb = c.getEntityB();

c.createEnemy(enemyCount);

}

如果你需要我展示另一堂课，我会很乐意这样做，因为最大和唯一的大赛（ish）就是游戏

**编辑：**这是getSpriteSheet方法

        `public BufferedImage getSpriteSheet(){ return spriteSheet; }`

** EDIT1：**这是BufferedImageLoader类

 package com.game.main;

import java.awt.image.BufferedImage;
import java.io.IOException;

import javax.imageio.ImageIO;

public class BufferedImageLoader {

    private BufferedImage image;

    public BufferedImage loadImage(String path) throws IOException{

        image = ImageIO.read(getClass().getResource(path));
        return image;
    }

}

** EDIT2：**当我尝试从头开始尝试时，我只是得到了这个错误，我也不认为我在遇到错误时犯了错误。所以病了，保持为/Sprite_Sheet.png;

Exception in thread "Thread-0" java.lang.IllegalArgumentException: input == null!
    at javax.imageio.ImageIO.read(ImageIO.java:1388)
    at com.game.main.BufferedImageLoader.loadImage(BufferedImageLoader.java:14)
    at com.game.main.Game.init(Game.java:72)
    at com.game.main.Game.run(Game.java:117)
    at java.lang.Thread.run(Thread.java:745)

** EDIT3：**我已经检查过是否只有spriteSheet加载为null，而且背景并没有给出null

**找到答案：**我格式化了错误，虽然它是PNG，但显然不对，所以我用不同的图像编辑器打开它并再次导出。

Answer 1

Game.spriteSheet成员在调用ss = new SpriteSheet(game.getSpriteSheet())时尚未初始化，由tex = new Textures(this)中的Game.init()触发。

奇怪的是，在Game.init()中，spriteSheet在new Texture(this)被调用之前被初始化。您可以在spriteSheet中使用spriteSheet = loader.loadImage("/Sprite_Sheet.png")的try / catch块后检查Game.init()是否为空。

为什么这似乎没有被初始化

1 个答案: