Thread: Java SnakeGame

Hi, im new to this and i tried to make a runnable snake game. When i try to run my code i get this:

Exception in thread "main" java.lang.NullPointerException
	at Game.Move(Game.java:85)
	at Game.run(Game.java:244)
	at Game.main(Game.java:38)

The game runs, but the snake doesn't move, and apples are spawned everywhere.
I can't post all the code, so here are Move, run and main code:

public static void main(String[] args) {
		JFrame frame = new JFrame("Snake");
		Game game = new Game();
		frame.add(game);
		frame.setSize(406, 430);
		frame.setVisible(true);
		frame.setResizable(false);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		game.run();
	}

public void run() {
		while (true) {
		Move();
		Draw(globalGraphics);
		repaint();
 
			try
			{
				Thread.currentThread();
				Thread.sleep(100);				
			}
			catch(Exception e)
			{
				e.printStackTrace();
			}	
		}
 
	}

public void Move()
	{
		Point head = snake.peekFirst();
		Point newPoint = head;
		switch (direction) {
		case Direction.NORTH:
			newPoint = new Point(head.x, head.y - 1);
			break;
		case Direction.SOUTH:
			newPoint = new Point(head.x, head.y + 1);
			break;
		case Direction.WEST:
			newPoint = new Point(head.x - 1, head.y);
			break;
		case Direction.EAST:
			newPoint = new Point(head.x + 1, head.y);
			break;
		}
 
		snake.remove(snake.peekLast());
 
		if (newPoint.equals(fruit))
		{
			score+=10;
 
			Point addPoint = (Point) newPoint.clone();
 
			switch (direction) {
			case Direction.NORTH:
				newPoint = new Point(head.x, head.y - 1);
				break;
			case Direction.SOUTH:
				newPoint = new Point(head.x, head.y + 1);
				break;
			case Direction.WEST:
				newPoint = new Point(head.x - 1, head.y);
				break;
			case Direction.EAST:
				newPoint = new Point(head.x + 1, head.y);
				break;
			}
 
			snake.push(addPoint);
			PlaceFruit();
 
		}
		else if (newPoint.x < 0 || newPoint.x > (GRID_WIDTH - 1))
		{
 
			GenerateDefaultSnake();
			return;
		}
		else if (newPoint.y < 0 || newPoint.y > (GRID_HEIGHT - 1))
		{
 
			GenerateDefaultSnake();
			return;
		}
		else if (snake.contains(newPoint))
		{
 
 
			GenerateDefaultSnake();
			return;
		}
 
 
		snake.push(newPoint);
	}

Welcome to the forum! Thanks for taking the time to learn how to post code correctly. If you haven't already, please read this topic to learn other useful info for new members.

Something in line 85 of Game's move() method is null. 'move() is improperly named 'Move()'. Add print statements or other indicators to determine which item is null and then fix it. (We can't tell which line is line 85 or which item is null even if we knew which line was line 85 from the code you've posted, so there's not much more we can do.)

So line 85 is:

Point head = snake.peekFirst();

The declaration of the variable:

private LinkedList<Point> snake;

The initialization of the snake variable in paint method + snake generator:

public void paint(Graphics g)
	{
		this.setPreferredSize(new Dimension(640, 480));
		snake = new LinkedList<Point>();
		GenerateDefaultSnake();
		PlaceFruit();
		globalGraphics = g.create();
		this.addKeyListener(this);
		if (runThread == null)
		{
			runThread = new Thread(this);
			runThread.start();
		}
	}
 
	public void GenerateDefaultSnake()
	{
		score = 0;
		snake.clear();
 
		snake.add(new Point(0,2));
		snake.add(new Point(0,1));
		snake.add(new Point(0,0));
		direction = Direction.NO_DIRECTION;
	}

Originally Posted by Norm

The paint() method is NOT a good place to initialize variables. paint() can be called for various reasons at different ttimes.
If the variable should be initialized one time, it better to do it in the constructor.

Same thing hapens

Originally Posted by Norm

Please copy the full text of the error message and paste it here.
Also post the new code that causes the error.

It's the same error message as above.

public void paint(Graphics g)
	{
		this.setPreferredSize(new Dimension(640, 480));
		GenerateDefaultSnake();
		PlaceFruit();
		globalGraphics = g.create();
		this.addKeyListener(this);
		if (runThread == null)
		{
			runThread = new Thread(this);
			runThread.start();
		}
	}
 
	public void GenerateDefaultSnake()
	{	
		snake = new LinkedList<Point>();
		score = 0;
		snake.clear();
 
		snake.add(new Point(0,2));
		snake.add(new Point(0,1));
		snake.add(new Point(0,0));
		direction = Direction.NO_DIRECTION;
	}

Exception in thread "main" java.lang.NullPointerException
	at Game.move(Game.java:85)
	at Game.run(Game.java:244)
	at Game.main(Game.java:38)

Ok so now the problem is with the draw method:

public void draw(Graphics g)
	{
		g.clearRect(0, 0, BOX_WIDTH * GRID_WIDTH + 10, BOX_HEIGHT * GRID_HEIGHT + 20);
 
		BufferedImage buffer = new BufferedImage(BOX_WIDTH * GRID_WIDTH + 10, BOX_HEIGHT * GRID_HEIGHT + 20, BufferedImage.TYPE_INT_ARGB);
		Graphics bufferGraphics = buffer.getGraphics();
 
		drawFruit(bufferGraphics);
		drawGrid(bufferGraphics);
		drawSnake(bufferGraphics);
		drawScore(bufferGraphics);
 
 
		g.drawImage(buffer, 0, 0, BOX_WIDTH * GRID_WIDTH + 10,  BOX_HEIGHT * GRID_HEIGHT + 20, this);
	}

Exception in thread "main" java.lang.NullPointerException
	at Game.draw(Game.java:68)
	at Game.run(Game.java:245)
	at Game.main(Game.java:38)

The line in cause is:

g.clearRect(0, 0, BOX_WIDTH * GRID_WIDTH + 10, BOX_HEIGHT * GRID_HEIGHT + 20);

I have a globalGraphics variable.

Declaration:

private Graphics globalGraphics;

Initialization(see in paint()):

globalGraphics = g.create();

draw(globalGraphics);

Yeah, i called the method before the initialization of global graphics so that gave me massiv eror. Now all is good. No erors, but still apples spawn every where and snake dose not move...

Originally Posted by Norm

Is the snake's x,y location being changed?

Make a small, complete program that compiles, executes and shows the problem. what is posted can't be used for testing.

the program runs, the snake is there but it dose not move when i pres key, and apples are spawning everywhere

Here is move method:

public void move()
	{
		if (direction == Direction.NO_DIRECTION)
			return;
 
		Point head = snake.peekFirst();
		Point newPoint = head;
		switch (direction) {
		case Direction.NORTH:
			newPoint = new Point(head.x, head.y - 1);
			break;
		case Direction.SOUTH:
			newPoint = new Point(head.x, head.y + 1);
			break;
		case Direction.WEST:
			newPoint = new Point(head.x - 1, head.y);
			break;
		case Direction.EAST:
			newPoint = new Point(head.x + 1, head.y);
			break;			
		}
 
			snake.remove(snake.peekLast());
 
		if(newPoint.equals(fruit))
		{	
			score+=10;
 
			Point addPoint = (Point) newPoint.clone();
 
			switch (direction){
			case Direction.NORTH:
				newPoint = new Point(head.x, head.y - 1);
				break;
			case Direction.SOUTH:
				newPoint = new Point(head.x, head.y + 1);
				break;
			case Direction.WEST:
				newPoint = new Point(head.x - 1, head.y);
				break;
			case Direction.EAST:
				newPoint = new Point(head.x + 1, head.y);
				break;			
			}
				snake.push(addPoint);
				placeFruit();							
 
		}
			else if(newPoint.x < 0 || newPoint.x > (GRID_WIDTH - 1))
			{						
				return;						
			}
			else if(newPoint.y < 0 || newPoint.y > (GRID_HEIGHT - 1))
			{				
				return;					
			}
			else if(snake.contains(newPoint))
			{				
				return;		
			}
			else if(snake.size() == (GRID_WIDTH * GRID_HEIGHT))
			{				
				return;
			}						
 
		snake.push(newPoint);
 
	}

And placeFruit method:

public void placeFruit()
	{
		Random rand = new Random();
		int randomX = rand.nextInt(GRID_WIDTH);
		int randomY = rand.nextInt(GRID_HEIGHT);
		Point randomPoint = new Point(randomX, randomY);
		while (snake.contains(randomPoint))
		{
			randomX = rand.nextInt(GRID_WIDTH);
			randomY = rand.nextInt(GRID_HEIGHT);
			randomPoint = new Point(randomX, randomY);
		}
		fruit = randomPoint;
	}

If you mean a runnable jar, here it is:SnakeGame.jar

Any luck?

Direction.txt
Game.txt