java - 为什么这似乎没有初始化

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)

而且我很确定我知道null在哪里，我认为这是此方法(也就是getImage方法会在我创建的spritesheet.png图像中所需的任何网格中加载)

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;

}

我已经看过了本类(class)的所有内容，这是该类(class):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; 
}
}

我想知道如何启动它？尽管我猜它已经是image.getSubimage(code)了，但是我测试了this.image并说那是NullPointerException ...但它应该已经启动了。

其他可能涉及的类

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很大，所以我将给出它所涉及的主要方法(得到它吗？init()，就在其中...)

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);

如果您需要我展示另一门课，我会很乐意这样做，因为最大(也是唯一)的是Game

**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:**当我从头开始尝试对其进行路径设置时，我只会遇到此错误，我也不认为在进行路径设置时也犯了一个错误。所以请把它保存为/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:**我检查了是否只有spriteSheet加载了null，而背景却没有返回null

**发现答案:**我格式化错误，尽管它是PNG，但显然不正确，因此我使用其他图像编辑器将其打开并再次导出。

Answer 1

调用Game.spriteSheet时，似乎ss = new SpriteSheet(game.getSpriteSheet())成员尚未初始化，这是由tex = new Textures(this)中的Game.init()触发的。

奇怪的是，在Game.init()中，在调用spriteSheet之前初始化了new Texture(this)。您可以在spriteSheet中使用spriteSheet = loader.loadImage("/Sprite_Sheet.png")的try/catch块之后检查Game.init()是否不为空。