Unable to identify where a NullPointerException is coming from - nullpointerexception

Question

so I am getting the following error:
Exception in thread "Thread-0" java.lang.NullPointerException
at dev.tamir.firstgame.entities.creatures.Player.getInput(Player.java:19)
at dev.tamir.firstgame.entities.creatures.Player.tick(Player.java:31)
at dev.tamir.firstgame.states.GameState.tick(GameState.java:25)
at dev.tamir.firstgame.Game.tick(Game.java:65)
at dev.tamir.firstgame.Game.run(Game.java:110)
at java.lang.Thread.run(Unknown Source)
And I've checked all the lines Java had marked me and I can not find what is producing the null.
Player:
package dev.tamir.firstgame.entities.creatures;
import java.awt.Graphics;
import dev.tamir.firstgame.Game;
import dev.tamir.firstgame.gfx.Assets;
public class Player extends Creature {
private Game game;
public Player(Game game, float x, float y) {
super(game, x, y, Creature.DEFAULT_CREATURE_WIDTH, Creature.DEFAULT_CREATURE_HEIGHT);
}
#Override
public void tick() {
getInput();
move();
game.getGameCamera().centerOnEntity(this);
}
private void getInput() {
xMove = 0;
yMove = 0;
if(game.getKeyManager().up)
yMove = -speed;
if(game.getKeyManager().down)
yMove = speed;
if(game.getKeyManager().left)
xMove = -speed;
if(game.getKeyManager().right)
xMove = speed;
}
#Override
public void render(Graphics g) {
g.drawImage(Assets.robro[7], (int) (x - game.getGameCamera().getxOffset()), (int) (y - game.getGameCamera().getyOffset()), width, height, null);
}
}
Gamestate:
package dev.tamir.firstgame.states;
import java.awt.Graphics;
import dev.tamir.firstgame.Game;
import dev.tamir.firstgame.entities.creatures.Player;
import dev.tamir.firstgame.tiles.Tile;
import dev.tamir.firstgame.worlds.World;
public class GameState extends State {
private Player player;
private World world;
public GameState(Game game) {
super(game);
player = new Player(game, 0, 0);
world = new World(game, "res/worlds/world1.txt");
}
#Override
public void tick() {
world.tick();
player.tick();
}
#Override
public void render(Graphics g) {
world.render(g);
player.render(g);
}
}
Game:
package dev.tamir.firstgame;
import java.awt.Graphics;
import java.awt.image.BufferStrategy;
import dev.tamir.firstgame.Display.Display;
import dev.tamir.firstgame.gfx.Assets;
import dev.tamir.firstgame.gfx.GameCamera;
import dev.tamir.firstgame.input.KeyManager;
import dev.tamir.firstgame.states.GameState;
import dev.tamir.firstgame.states.MenuState;
import dev.tamir.firstgame.states.State;
public class Game implements Runnable {
private Display display;
private Thread thread;
private BufferStrategy bs;
private Graphics g;
//States
private State gameState;
private State menuState;
//Input
private KeyManager keyManager;
//Camera
private GameCamera gameCamera;
private boolean running = false;
private int width, height;
public String title;
public Game(String title, int width, int height) {
this.width = width;
this.height = height;
this.title = title;
keyManager = new KeyManager();
}
private void init() {
display = new Display(title, width, height);
display.getFrame().addKeyListener(keyManager);
Assets.init();
gameCamera = new GameCamera(this, 0,0);
gameState = new GameState(this);
menuState = new MenuState(this);
State.setState(gameState);
}
private void tick() {
keyManager.tick();
if(State.getState() != null)
State.getState().tick();
}
private void render() {
bs = display.getCanvas().getBufferStrategy();
if(bs == null) {
display.getCanvas().createBufferStrategy(3);
return;
}
g = bs.getDrawGraphics();
//Clear
g.clearRect(0, 0, width, height);
//Draw
if(State.getState() != null)
State.getState().render(g);
//End of Draw
bs.show();
g.dispose();
}
public void run() {
init();
int fps = 60;
double timePerTick = 1000000000 / fps;
double delta = 0;
long now;
long lastTime = System.nanoTime();
long timer = 0;
int ticks = 0;
while (running) {
now = System.nanoTime();
delta += (now - lastTime) / timePerTick;
timer += now - lastTime;
lastTime = now;
if(delta >= 1) {
tick();
render();
ticks++;
delta--;
}
if(timer >= 1000000000) {
System.out.println("FPS: " + ticks );
ticks = 0;
timer = 0;
}
}
stop();
}
public KeyManager getKeyManager() {
return keyManager;
}
public GameCamera getGameCamera() {
return gameCamera;
}
public int getWidth() {
return width;
}
public int getHeight() {
return height;
}
public synchronized void start() {
if (running)
return;
running = true;
thread = new Thread(this);
thread.start();
}
public synchronized void stop() {
if (!running)
return;
running = false;
try {
thread.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
help would be very appreciated, as I've been looking for hours now and I don't know what is causing the null and I am suspecting the error log may even be misleading me.

Answer 1

My guess would be you have a private Game in your creature class. When you call super() in Player, you pass a Game object to Creature. The Creature constructor most likely has a line like this.game = game;
Of course, I can't say for sure because the Creature class is not included in your post, but that's the most likely code setup. Because game would then be private to Creature, Player cannot see it. That means the private Game game that you declare in Player is never set.
After you call super, do this.game = game;
This will almost certainly take care of your issue.
Just for future reference, the message you got when the error resulted is the call stack; basically it tells you what methods called what, the most recent being at the top. The error took place at line 19 in Player.getInput(), which was called by tick() in that same class.
The only object you use in getInput() is game, and so that must be the source of the null pointer. From there, it's a quick check to see that game is a private field of Player, and since it is null that's a huge clue that it was never initialized (though that is not always the case). Private fields most often are initialized in the class constuctor (but they don't have to be... your Player class is pretty sparse so it wouldn't take that long to look through all of it if you absolutly had to. Looking at the Player constructor, we see a Game object named game is passed in, which suggests that it was intended to be used to initialize game and yet never is. Voilà, we found the problem!
I'm sorry if that last paragraph felt a little condecending; it wasn't meant to be. I just wanted to walk you through how I found your issue. Hopefully knowing how I found it will help you find later errors on your own.