Pfthb

Actual question on the bottom of the post!


At first, I want to explain my problem.

I'm writing a basic Snake game and I got the snake to move automatically. It moves automatically to the right of the window when you execute the code, just like intended. However, I can't steer my snake the way I want, it doesn't change its direction at all.

To avoid confusion, player is an instance of the class Snake.

To explain the movement of the snake:

The Snake object has a coordinates property which is an ArrayList holding SnakePart objects. Each SnakePart object has the property x and y. Using this ArrayList, the snake is moving by drawing little rectangles on a canvas by using the x and y properties on the y- and x-axis of the canvas.

The Snake object also has a dx and a dy property that gets added (or subtracted -- depending on the direction of the snake) to the x and y property of the SnakePart object to move the snake in a direction.

To update the ArrayList in Snake.java:

public void move() 
 SnakePart head = new SnakePart(this.coordinates.get(0).x + this.dx, this.coordinates.get(0).y + this.dy);

 this.coordinates.add(0, head);
 this.coordinates.remove(this.coordinates.size() - 1);

To draw the snake on the canvas in Board.java (partly, rest of the method is not necessary for now):

@Override
public void paintComponent(Graphics g) 
 this.player.coordinates.forEach(snakePart -> 
 g.setColor(Color.BLUE);
 g.fillRect(snakePart.x, snakePart.y, 10, 10);
 );

To steer the snake, I want to use the arrow keys. Depending on which arrow key is pressed, the snake's x and y coordinates/properties get modified (Board.java):

@Override
public void keyPressed(KeyEvent event) 
 int keyCode = event.getKeyCode();

 if (keyCode == 37) 
 this.player.dx = -10;
 this.player.dy = 0;
 else if (keyCode == 38) 
 this.player.dx = 0;
 this.player.dy = -10;
 else if (keyCode == 39) 
 this.player.dx = 10;
 this.player.dy = 0;
 else if (keyCode == 40) 
 this.player.dx = 0;
 this.player.dy = 10;
 

Whole code:

Snake.java:

package com.codef0x.snake;
import java.util.ArrayList;

public class Snake 
 ArrayList < SnakePart > coordinates;
 int dx = 10;
 int dy = 0;

 public Snake(ArrayList < SnakePart > coords) 
 this.coordinates = coords;
 

 public void move() 
 SnakePart head = new SnakePart(this.coordinates.get(0).x + this.dx, this.coordinates.get(0).y + this.dy);

 this.coordinates.add(0, head);
 this.coordinates.remove(this.coordinates.size() - 1);
 

 public void grow() 
 SnakePart newPart = new SnakePart(0, 0);
 newPart.x = this.coordinates.get(this.coordinates.size() - 1).x - 10;
 newPart.y = this.coordinates.get(this.coordinates.size() - 1).y;

 this.coordinates.add(this.coordinates.size() - 1, newPart);
 

Board.java (showing only relevant parts, otherwise it would be too much code)

package com.codef0x.snake;

import javax.swing.*;
import java.awt.*;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.util.ArrayList;
import java.util.Timer;
import java.util.TimerTask;


public class Board extends JPanel implements KeyListener 
 Snake player;
 ArrayList<SnakePart> snakeCoordinates;

 public Board() 

 this.snakeCoordinates = new ArrayList<>();

 snakeCoordinates.add(new SnakePart(150, 150));
 snakeCoordinates.add(new SnakePart(140, 150));
 snakeCoordinates.add(new SnakePart(130, 150));
 snakeCoordinates.add(new SnakePart(120, 150));

 this.player = new Snake(snakeCoordinates);

 this.food = new Food();
 

 @Override
 public void paintComponent(Graphics g) 
 clear(g);

 this.player.coordinates.forEach(snakePart - > 
 g.setColor(Color.BLUE);
 g.fillRect(snakePart.x, snakePart.y, 10, 10);
 );
 

 public void clear(Graphics g) 
 g.clearRect(0, 0, getHeight(), getWidth());
 

 @Override
 public void update(Graphics g) 
 paintComponent(g);
 

 @Override
 public void keyPressed(KeyEvent event) 
 int keyCode = event.getKeyCode();

 if (keyCode == 37) 
 this.player.dx = -10;
 this.player.dy = 0;
 else if (keyCode == 38) 
 this.player.dx = 0;
 this.player.dy = -10;
 else if (keyCode == 39) 
 this.player.dx = 10;
 this.player.dy = 0;
 else if (keyCode == 40) 
 this.player.dx = 0;
 this.player.dy = 10;
 
 

 @Override
 public void keyTyped(KeyEvent event) 
 return;
 

 @Override
 public void keyReleased(KeyEvent event) 
 return;
 

 public void run(Board board) 
 Timer game = new Timer();
 game.schedule(new TimerTask() 
 boolean initiallySpawned = false;
 @Override
 public void run() 
 Graphics g = board.getGraphics();

 if (hitSomething()) // removed method hitSomething, not relevant
 game.cancel();
 return;
 

 player.move();
 update(g);
 
 , 0, 500);
 

SnakePart.java:

package com.codef0x.snake;

public class SnakePart 
 int x;
 int y;

 public SnakePart(int x, int y) 
 this.x = x;
 this.y = y;
 

What am I doing wrong and what do I need to change to steer the snake properly?

In case you still want / need to see all files as a whole, you can have a look at them here:

Snake.java

Board.java

SnakePart.java

Food.java <- Not related, but may prevent confusion about the Food object

The problem is in the main.
You create a board to host your game status, and create different one to listen to the keyboard.

public static void main(String args) 

 JFrame frame = new JFrame("Snake");
 frame.setDefaultCloseOperation(3);

 Board board = new Board();
 frame.add(board);
 frame.setSize(500, 500);
 frame.addKeyListener(new Board());
 frame.setVisible(true);

 board.run(board);

it should be:

public static void main(String args) 

 JFrame frame = new JFrame("Snake");
 frame.setDefaultCloseOperation(3);

 Board board = new Board();
 frame.add(board);
 frame.setSize(500, 500);
 frame.addKeyListener(board);
 frame.setVisible(true);


 board.run(board);

Also board.run(board) has little sense, in the scope of run method, board can be swapped to this (and so omitted) ...