java - 我收到错误 "AWT-EventQueue-0"java.lang.NullPointerException 并且我不明白为什么在我的上下文中

Question

我正在制作一个游戏，并有一个类来打印屏幕上的所有内容。我在这一行收到错误: g.drawImage(chImage, imageP.x*scale, imageP.y*scale, null); 是因为我末尾有 null 吗？我查找了这个错误并试图找出它，我知道该行中的某些内容为空，但我无法弄清楚什么是空或如何修复它。如果您需要我发布其他类(class)，我可以。到目前为止，从我的谷歌搜索来看，我认为这可能与我的变量初始化方式有关。

package Game;

import java.awt.Graphics;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.image.BufferedImage;
import java.util.ArrayList;

import javax.swing.JPanel;

public class Printer extends JPanel{
private Map map;
private Character ch;
private int scale;
private Point imageP;
private BufferedImage chImage;
private ArrayList<Rectangle> part;

public Printer(int scale1){
    scale = scale1;
    map = new Map();
    ch = new Character();
    imageP = ch.getPoint();
    chImage = ch.getImage();
    part = map.setPart();
}


protected void paintComponent(Graphics g) {
    super.paintComponent(g);

    g.drawImage(chImage, imageP.x*scale, imageP.y*scale, null);

    for(int i=0; i<part.size(); i++){
        Rectangle temp = new Rectangle(part.get(i));
        g.drawRect(temp.x, temp.y, temp.width, temp.height);
        g.fillRect(temp.x, temp.y, temp.width, temp.height);
    }


}

}


package Game;

import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

import javax.imageio.ImageIO;
import javax.swing.JPanel;

//Creates a image for a character and allows him to walk around the screen
public class Character extends JPanel{

private BufferedImage image;
private Point imageP;
private int speed;
private int scale;
private int width;
private int height;

public Character(){

}

public Character(int x, int y, int scale1, int w, int h){
   super();
   try {
        image = ImageIO.read(new File("F:\\Programming\\Final Project\\Top_down\\narwhal.png"));
   } catch (IOException ex) {

   }
   scale = scale1;
   imageP = new Point(x,y);
   speed = 10;
   width = w;
   height = h;
   addKeyListener(new KeyAdapter(){
       @Override
   public void keyPressed(KeyEvent evt){
           moveIt(evt);
       }
   });
}


public void moveIt(KeyEvent evt){
    switch(evt.getKeyCode()){
    case KeyEvent.VK_S:
        if(imageP.y <= height-33)
            imageP.y += 1*speed;
        break;
    case KeyEvent.VK_W:
        if(imageP.y >=0+5)
            imageP.y -= 1*speed;
        break;
    case KeyEvent.VK_A:
        if(imageP.x >=0+5)
            imageP.x -= 1*speed;
        break;
    case KeyEvent.VK_D:
        if(imageP.x <= width-30)
            imageP.x += 1*speed;
        break;
    }
    repaint();
}


public Point getPoint(){
    //g.drawImage(image, imageP.x*scale, imageP.y*scale, null);  IGNORE THIS
    return this.imageP;
}

public BufferedImage getImage(){
    return this.image;
}


}

Answer 1

确保您的 chImage 实际上是一个 Image。换句话说，一个简单的测试就是打印到 System.out，这里是一个示例:

    System.out.println("chImage: " + chImage);

如果 chImage 在输出中打印类似 AwtImage@17089 的内容，则它会被加载。如果 if 在该位置显示为 null，则表示没有加载图像。检查您的图像路径(如果发生这种情况)，或者图像名称拼写是否正确。