Error In Java: IllegalArgumentException

Question

I am working on a game and I am getting this error for my code:

Exception in thread "main" java.lang.IllegalArgumentException: input == null!
    at javax.imageio.ImageIO.read(Unknown Source)
    at com.mcserverpros.game.gfx.SpriteSheet.<init>(SpriteSheet.java:21)
    at com.mcserverpros.game.Game.<init>(Game.java:32)
    at com.mcserverpros.game.Game.main(Game.java:146)

This is my Game.java class:

package com.mcserverpros.game;

import java.awt.BorderLayout;
import java.awt.Canvas;
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;

import com.mcserverpros.game.gfx.SpriteSheet;

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 = "Game";

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();

public SpriteSheet spriteSheet = new SpriteSheet("/sprite_sheet.png");

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

}

public synchronized void stop() {
    running = false;
}

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

    int frames = 0;
    int ticks = 0;

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

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

        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 + " ticks" + ", " + frames + " 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;
    }

    Graphics g = bs.getDrawGraphics();
    g.drawImage(image, 0, 0, getWidth(), getHeight(), null);

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

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

And this is my SpriteSheet.java class

package com.mcserverpros.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]);
    }
 }
}

Answer 1

Check this line:

ImageIO.read(SpriteSheet.class.getResourceAsStream(path))

It seems that SpriteSheet.class.getResourceAsStream(path) is returning a null value. It's quite possible that path isn't pointing to an actual file in the filesystem. Notice that you're passing "/sprite_sheet.png", that's a path relative to the source code's directory. Take a look at this post to get an idea of how you can build a relative path that works. If all else fails you could use an absolute path, but that won't be portable.