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Thread: Java SnakeGame

  1. #1
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    Default 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);
    	}


  2. #2
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    Default Re: Java SnakeGame

    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.)

  3. #3
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    Default Re: Java SnakeGame

    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;
    	}

  4. #4
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    Default Re: Java SnakeGame

    initialization of the snake variable in paint method
    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.
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Java SnakeGame

    Quote Originally Posted by Norm View Post
    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

  6. #6
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    Default Re: Java SnakeGame

    Please copy the full text of the error message and paste it here.
    Also post the new code that causes the error.
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Java SnakeGame

    Quote Originally Posted by Norm View Post
    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.

  8. #8
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    Default Re: Java SnakeGame

    It can't be if you changed the program.
    If you didn't change the program, nothing will change and it will be the same.
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Java SnakeGame

    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)

  10. #10
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    Default Re: Java SnakeGame

    The code STILL has the call to the method: GenerateDefaultSnake() INSIDE of the paint() method.
    Code that is used one time to initialize variables should NOT be in the paint() method.
    Move the call to that method out of paint().
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Java SnakeGame

    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);

  12. #12
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    Default Re: Java SnakeGame

    Does g have a null value? How is the draw() method called? Where is the args passed to draw() given a value?
    If you don't understand my answer, don't ignore it, ask a question.

  13. #13
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    Default Re: Java SnakeGame

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

    public void paint(Graphics g)
    	{
    		this.setPreferredSize(new Dimension(640, 480));
    		placeFruit();
    		globalGraphics = g.create();
    		this.addKeyListener(this);
    		if (runThread == null)
    		{
    			runThread = new Thread(this);
    			runThread.start();
    		}
    	}
    I did not initialize g.
    I only use repaint().
    Last edited by RigaCrypto; April 21st, 2014 at 11:39 AM.

  14. #14
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    Default Re: Java SnakeGame

    The draw() method should be called from the paint() method because that is where the Graphics object is.
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Java SnakeGame

    I have a globalGraphics variable.

    Declaration:
    private Graphics globalGraphics;
    Initialization(see in paint()):
    globalGraphics = g.create();
    draw(globalGraphics);

  16. #16
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    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Java SnakeGame

    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...

  18. #18
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    Default Re: Java SnakeGame

    snake dose not move
    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.
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Java SnakeGame

    Quote Originally Posted by Norm View Post
    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;
    	}

  20. #20
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    Default Re: Java SnakeGame

    Can you Make a small, complete program that compiles, executes and shows the problem?
    If you don't understand my answer, don't ignore it, ask a question.

  21. #21
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    Default Re: Java SnakeGame

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

  22. #22
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    Default Re: Java SnakeGame

    I need a source for debugging.
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Java SnakeGame

    Any luck?

  24. #24
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    Default Re: Java SnakeGame

    I need a source file for debugging. I do NOT download from other sites.
    If you don't understand my answer, don't ignore it, ask a question.

  25. #25
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    Default Re: Java SnakeGame

    Direction.txt
    Game.txt

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