NullPointerException with Graphics2D Translate

Question

I'm not having any problems fixing this. I'm creating a game and I constructed a camera to follow a player when they are moving but when I use the method translate from the Graphics2D class I get a null pointer.

This problem doesn't happen all the time, sometimes when I run the game the error occurs?

All objects are created for Gr

Exception in thread "Thread-3" java.lang.NullPointerException
at game.Game.render(Game.java:172)
at game.Game.run(Game.java:126)
at java.lang.Thread.run(Thread.java:745)

It's pointing at this line here.

    g2d.translate(cam.getX(), cam.getY());  

In my render method.

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

    Graphics g = bs.getDrawGraphics();
    Graphics2D g2d = (Graphics2D) g; 

    g.setColor(Color.BLACK);
    g.fillRect(0, 0, WIDTH, HEIGHT);

    g2d.translate(cam.getX(), cam.getY());      

    handler.render(g);

    g2d.translate(-cam.getX(), -cam.getY());

    if (gameState == STATE.GAME) {
        hud.render(g);
    } else if (gameState == STATE.MENU || gameState == STATE.HELP ||    gameState == STATE.END) {
        menu.render(g);
    }
    g.dispose();
    bs.show();
}

Any ideas?

cam is coming from this code:

public Game() {

    tex = new Texture();

    handler = new Handler();
    hud = new HUD();
    menu = new Menu(this, handler, hud);
    this.addKeyListener(new KeyInput(handler));
    this.addMouseListener(menu);

    new Window(WIDTH, HEIGHT, "Let's Build A Game", this);

    spawner = new Spawn(handler, hud);

//      loader = new BufferedImageLoader();
//      background = loader.loadImage("/level.png");
//      
//      loadImageLevel(background);

    cam = new Camera(0, 0);

    if (gameState == STATE.MENU) {
        handler.createMenuParticle();
    } else {
        handler.clearEnemies();
    }
}

This is the camera class I use.

public class Camera {

private float x, y;

public Camera(float x, float y) {
    this.x = x;
    this.y = y;
}

public void tick(GameObject player) {
    x = -player.getX() + (Game.WIDTH / 2);
    y = -player.getY() + (Game.HEIGHT / 2);
}

public float getX() {
    return x;
}

public void setX(float x) {
    this.x = x;
}

public float getY() {
    return y;
}

public void setY(float y) {
    this.y = y;
}
}

Answer 1

Since the stacktrace doesn't go any deeper, it can only be g2d and cam that may be the cause of the exception. Since you used g2d before (as g) and it worked, the problem must be cam, which is most likely null at that point.

EDIT: From your edit I can see that cam is initialized properly in the class' constructor you show us. So one of the following is likely happening:

1. There is another constructor that doesn't initialize cam.
2. There is some other code that overwrites cam.
3. Your render method is called before cam is set in the constructor. Try to make the cam initialization the first line of the constructor to check for this. It also might be a good idea to not launch GUI stuff in your Game constructor at all.

You should look for code that does either of those three things. Set breakpoints at the relevant lines to check, if and when they are executed.