Java Snake Game Problem

[siddharth sekhar]

Hello , I am trying to make the classic snake game in Java and facing some issues , well I am able to do some of the coding but not able to understand some of it and not able to implement some of the logic. The problem that I am facing is that if the snake is going up and I press the down key then the snake move on itself and the games ends , same thing happens on side , it is moving right and I press the left arrow key the snake moves on itself and the game is over . So how and I stop the snake to move on itself . The code when the snake eats one of its body part is

	public void snakeNoMore() {
		for (int i = 0; i < tail.size(); i++) {
			 SnakeClass obj = tail.get(i);
				
             double d = Math.sqrt(Math.pow((this.xpos - obj.xpos), 2) + Math.pow((this.ypos - obj.ypos), 2));
			 
             if(d < 1){
			 ControlClass.endGame();
			 }
		}

	}

And I am not able to understand the logic behind this piece of code which adds a new snake body part when the snake eats food

	if (total > 0) {
			if (total == tail.size() && !tail.isEmpty()) {
				tail.remove(0);
			}
			tail.add(new SnakeClass(xpos, ypos));
		}

the complete program is this

Class with the main function

public class MainClass {

	final static int WIDTH = 600;
	final static int HEIGHT = 600;
	
	public static void main(String[] args) {
	
		JFrame frame = new JFrame("SNAKE GAME PROTOTYPE");
		
		frame.setSize(WIDTH, HEIGHT);
		frame.add(new ControlClass());
		frame.setVisible(true);
		frame.setResizable(false);
		
		frame.setLocationRelativeTo(null);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		
	}

}

The JPanel Class

public class ControlClass extends JPanel implements ActionListener, KeyListener {

	SnakeClass sc;
	FoodClass fc;
	int scl = 20;
	Random random;

	ControlClass() {

		random = new Random();
		scl = 20;
		sc = new SnakeClass();
		// fc = new FoodClass((MainClass.WIDTH - 100)+
		// 50,random.nextInt(MainClass.HEIGHT - 100) + 50);
		this.pickAfoodLocation();
		Timer time = new Timer(600, this);
		time.start();

		this.addKeyListener(this);
		this.setFocusable(true);

	}

	public void paintComponent(Graphics g) {

		super.paintComponent(g);
		Graphics2D g2d = (Graphics2D) g;

		g2d.setColor(Color.BLACK);
		g2d.fillRect(0, 0, MainClass.WIDTH, MainClass.HEIGHT);

		sc.drawTheSnake(g2d);
		fc.drawTheFood(g2d);

	}

	public void pickAfoodLocation() {

		int cols = MainClass.WIDTH / scl;
		int rows = MainClass.HEIGHT / scl;

		fc = new FoodClass(random.nextInt(cols), random.nextInt(rows));

		fc.xpos = fc.xpos * scl;
		fc.ypos = fc.ypos * scl;

	}

	public void update() {
		
		sc.snakeNoMore();
		sc.directionChecking();
		sc.snakeEdgeLogic();
		sc.moveTheSnake();
		sc.snakeEdgeLogic();
		if (sc.didSnakeEatTheFood(fc)) {
			this.pickAfoodLocation();
		}

	}

	public static void endGame() {
		JOptionPane.showMessageDialog(null, "Game Over","GAME OVER",JOptionPane.YES_NO_OPTION);
		System.exit(ABORT);
	}

	

	@Override
	public void actionPerformed(ActionEvent e) {
		// Game Loop
		this.repaint();
		this.update();
	}

	@Override
	public void keyTyped(KeyEvent e) {
		// TODO Auto-generated method stub

	}

	@Override
	public void keyPressed(KeyEvent e) {
		sc.keyPressed(e);

	}

	@Override
	public void keyReleased(KeyEvent e) {

	}

}

The Snake Class

public class SnakeClass {

	int xpos, ypos;
	int xVelo, yVelo;
	int xDir, yDir;
	int scl = 20;;
	int total;
	int siz;
	Color color = new Color(255, 0, 0, 255);

	ArrayList<SnakeClass> tail = new ArrayList<SnakeClass>();

	SnakeClass() {

		xpos = MainClass.WIDTH / 2;
		ypos = MainClass.HEIGHT / 2;

		xVelo = 1;
		yVelo = 0;

		xDir = 1;
		yDir = 0;

		scl = 20;

		total = 0;

	}

	SnakeClass(int xpos, int ypos) {
		this.xpos = xpos;
		this.ypos = ypos;

	}

	public void drawTheSnake(Graphics2D g2d) {
		//////////////////////////

		g2d.setColor(Color.white);

		for (int i = 0; i < tail.size(); i++) {
			g2d.drawRect(tail.get(i).xpos, tail.get(i).ypos, scl, scl);
		}
		//////////////////////////

		g2d.setColor(this.color);
		g2d.drawRect(xpos, ypos, scl, scl);

	}

	public void moveTheSnake() {

		//////////////////////////
		if (total > 0) {
			if (total == tail.size() && !tail.isEmpty()) {
				tail.remove(0);
			}
			tail.add(new SnakeClass(xpos, ypos));
		}

		/////////////////////////

		xpos = xpos + (scl * xDir);
		ypos = ypos + (scl * yDir);

	}

    //when the snake hits a edge the end game method is called
	public void snakeEdgeLogic() {

		if (xpos > MainClass.WIDTH - scl) {
			xpos = MainClass.WIDTH - scl;
			ControlClass.endGame();
		}
		if (xpos < 0) {
			xpos = 0;
			ControlClass.endGame();
		}

		if (ypos > MainClass.HEIGHT - scl) {
			ypos = MainClass.HEIGHT - scl;
			ControlClass.endGame();
		}
		if (ypos < 0) {
			ypos = 0;
			ControlClass.endGame();
		}

	}

	public boolean didSnakeEatTheFood(FoodClass food) {

		if (this.getSnakeBounds().intersects(food.getFoodBounds())) {
			this.total++;
			SoundClass.SnakeEatApple.play();
			return true;
		} else
			return false;

	}

	public int getScore() {
		return total;
	}

    //when the snake hits on of its own body parts the eng game method is called
	public void snakeNoMore() {
		for (int i = 0; i < tail.size(); i++) {
		
			if (this.getSnakeBounds().intersects(tail.get(i).getSnakeBounds())) {
			ControlClass.endGame();

			//what should i do to stop the snake going back on itself and ending the game
			
			                                                                    }
		
		                                      }
	                          }
	
	
	public void changeSnakeDirection(int xDir, int yDir) {
		this.xDir = xDir;
		this.yDir = yDir;
	}

	public void keyPressed(KeyEvent e) {

		if (e.getKeyCode() == KeyEvent.VK_UP) {
			this.changeSnakeDirection(0, -1);
		}

		if (e.getKeyCode() == KeyEvent.VK_DOWN) {
			this.changeSnakeDirection(0, 1);
		}

		if (e.getKeyCode() == KeyEvent.VK_LEFT) {
			this.changeSnakeDirection(-1, 0);
		}
		if (e.getKeyCode() == KeyEvent.VK_RIGHT) {
			this.changeSnakeDirection(1, 0);
		}

		if (e.getKeyCode() == KeyEvent.VK_SPACE) {
			this.total++;
		}

	}

    //returns the current position of snake head
	public Rectangle getSnakeBounds() {
		return new Rectangle(xpos, ypos, scl, scl);
	}

}

The Food Class

public class FoodClass {

	
	int xpos,ypos;
	
	int scl = 20;
	
	Random random;
	
	FoodClass(int xpos,int ypos){
		this.xpos = xpos;
		this.ypos = ypos;
	}
	
	public void drawTheFood(Graphics2D g2d) {
		
		g2d.setColor(Color.green);
		g2d.fillRect(xpos, ypos, scl, scl);
		
	}
	
	public void foodLogic(){
		
	}
	
	public Rectangle getFoodBounds(){
		return new Rectangle(xpos,ypos,scl,scl);
	}

}

Thank you and have a nice day : )

[Dave Tolls]

In the changeSnakeDirection code just check if the new value is equal to the old value * -1.
If it is then don't change it.
That should prevent the reversing.

[Dave Tolls]

Actually, only allow the value to change if it is currently zero, or is being changed to zero.

Has the same effect, but might look simpler.

[siddharth sekhar]

Dave Tolls wrote:In the changeSnakeDirection code just check if the new value is equal to the old value * -1.
If it is then don't change it.
That should prevent the reversing.

It worked , Thanks for your suggestion , you are very good  : )

[Dave Tolls]

Well, you might hit an issue with diagonals, if they're allowed (not the case with traditional snake, though).