java - 当我尝试运行游戏时，我不断收到 (Suspending(NullPointerException))，但我无法在任何地方找到错误

Question

我的代码中不断出现错误，但我在任何地方都找不到它，它是在我添加 Spritesheet 和 Screen 类时开始的，这是堆栈:

Thread [Thread-2] (Suspended (exception NullPointerException))  
Screen.render(int[], int, int) line: 51 
Game.render() line: 128 
Game.run() line: 101    
Thread.run() line: not available    

`

第 51 行是这一行:

int colour = tileIndex * 4 + sheet.pixels[sheetPixel++];

这是 Screen 类:

package ca.vanzeben.game.gfx;

public class Screen {

    public static final int MAP_WIDTH = 64;
    public static final int MAP_WIDTH_MASK = MAP_WIDTH - 1 ;

    public int[] tiles = new int[MAP_WIDTH*MAP_WIDTH];
    public int[] colours = new int[MAP_WIDTH*MAP_WIDTH*4];

    public int xOffset = 0;
    public int yOffset = 0;

    public int width;
    public int height;

    public SpriteSheet sheet;

    public Screen(int width, int height, SpriteSheet sheet) {
        this.width = width;
        this.height = height;
        this.sheet = sheet;

        for (int i = 0; i<MAP_WIDTH*MAP_WIDTH; i++) {
            colours [i*4+0] = 0xff00ff;
            colours [i*4+1] = 0x00ffff;
            colours [i*4+2] = 0xffff00;
            colours [i*4+3] = 0xffffff;
        }
    }

    public void render(int[] pixels, int offset, int row) {
        for (int yTile = yOffset >>3;yTile <= (yOffset+height)>>3;yTile++) {
            int yMin = yTile * 8 - yOffset;
            int yMax = yMin + 8;
            if (yMin < 0) yMin = 0;
            if (yMax > height) yMax = height;

            for (int xTile = xOffset >>3;xTile <= (xOffset+width)>>3;xTile++) {
                int xMin = xTile * 8 - xOffset;
                int xMax = xMin + 8;
                if (xMin < 0) xMin = 0;
                if (xMax > width) xMax = width;

                int tileIndex = (xTile & (MAP_WIDTH_MASK))+ (yTile &(MAP_WIDTH_MASK))*MAP_WIDTH;

                for (int y = yMin; y <yMax; y++) {
                    int sheetPixel = ((y + yOffset)& 7)* sheet.width + ((xMin + xOffset) & 7);
                    int tilePixel = offset + xMin + y*row;
                    for (int x = xMin; x<xMax; x++) {
                        int colour = tileIndex * 4 + sheet.pixels[sheetPixel++];
                        pixels [tilePixel++] = colours [colour];
                    }
                }
            }
        }
    }
}

这是游戏类:

package ca.vanzeben.game;

import java.awt.BorderLayout;
import java.awt.Canvas;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.image.BufferStrategy;
import java.awt.image.BufferedImage;
import java.awt.image.DataBufferInt;

import javax.swing.JFrame;


public class Game extends Canvas implements Runnable {


    private static final long serialVersionUID = 1L;

    public static final int WIDTH = 160;
    public static final int HEIGHT = WIDTH /12*9;
    public static final int SCALE =3;
    public static final String NAME = "Wake Me Up";

    private JFrame frame;

    public boolean running = false;
    public int tickCount = 0;

    private BufferedImage image = new BufferedImage     (WIDTH,HEIGHT,BufferedImage.TYPE_INT_RGB);
    private int[] pixels =((DataBufferInt)image.getRaster().getDataBuffer()).getData();

    private Screen screen;

    public Game() {
        setMinimumSize(new Dimension (WIDTH*SCALE,HEIGHT*SCALE));
        setMaximumSize(new Dimension (WIDTH*SCALE,HEIGHT*SCALE));
        setPreferredSize(new Dimension (WIDTH*SCALE,HEIGHT*SCALE));

        frame = new JFrame(NAME);

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLayout(new BorderLayout());

        frame.add(this,BorderLayout.CENTER);
        frame.pack();

        frame.setResizable(false);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public void init() {
        screen = new Screen (WIDTH,HEIGHT, new SpriteSheet("/sprite_sheet.xcf"));
    }


    public synchronized void start() {
        running = true;
        new Thread(this).start();

    }

    public synchronized void stop() {

    }

    public void run() {
        long lastTime = System.nanoTime();
        double nsPerTick = 1000000000D/60D;

        int frames = 0;
        int ticks = 0;

        long lastTimer = System.currentTimeMillis();
        double delta = 0;

        init();

        while (running) {
            long now = System.nanoTime();
            delta += (now-lastTime) / nsPerTick;
            lastTime = now;
            boolean shouldRender = true;

            while (delta >=1) {
                ticks++;
                tick();
                delta -= 1;
                shouldRender = true;
            }
            try {
                Thread.sleep(2);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            if (shouldRender) {
                frames++;
                render();
            }

            if (System.currentTimeMillis()-lastTimer>=1000) {
                lastTimer += 1000;
                System.out.println(ticks+ "," +frames);
                frames = 0;
                ticks = 0;
            }
        }
    }

    public void tick() {
        tickCount++;    

        for (int i=0; i < pixels.length;i++) {
            pixels[i] = i+tickCount;
        }
    }

    public void render() {
        BufferStrategy bs = getBufferStrategy();
        if (bs == null) {
            createBufferStrategy(3);
            return;
        }

        screen.render(pixels, 0, WIDTH);

        Graphics g = bs.getDrawGraphics();

        g.setColor(Color.BLACK);
        g.fillRect(0, 0, getWidth(), getHeight());

        g.drawImage(image, 0, 0, getWidth(), getHeight(), null);

        g.dispose();
        bs.show();
    }

    public static void main(String[]args) {
        new Game().start();
    }

}

这是 SpriteSheet 类:

package ca.vanzeben.game.gfx;

import java.awt.image.BufferedImage;
import java.io.IOException;
import javax.imageio.ImageIO;

public class SpriteSheet {

    public String path;
    public int width;
    public int height;

    public int [] pixels;

    public SpriteSheet(String path) {
        BufferedImage image = null;
        try {

            image = ImageIO.read(SpriteSheet.class.getResourceAsStream(path));
        } catch (IOException e) {
            e.printStackTrace();
        }
        if (image == null) {
            return;
        }

        this.path = path;
        this.width = image.getWidth();
        this.height = image.getHeight();

        pixels = image.getRGB(0, 0, width, height, null, 0, width);

        for(int i = 0; i< pixels.length;i++) {
            pixels[i] = (pixels[i] & 0xff)/64;
        }

        for(int i = 0; i<8;i++) {
            System.out.println(pixels[i]);
        }
    }  
}

通常我不会寻求帮助，但我只是可以在任何地方找到错误。谢谢!

Answer 1

最可能的解释是 sheet.pixels 为 null(如果 sheet 本身为 null，则会在较早的线路上获得 NPE)。