Good day, how can you change the direction of the snake so that it does not go in the opposite direction immediately & lt; – & gt ;.

import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.control.Button;
import javafx.scene.input.KeyCode;
import javafx.scene.input.KeyEvent;
import javafx.scene.layout.StackPane;
import javafx.scene.paint.Paint;
import javafx.stage.Stage;
public class CanvasEx extends Application {
  final int size = 500, dot_size = 10, up = 1, right = 2, down = 3, left = 4;
  int delay = 50, length = 3, dir = 2, food_x, food_y;
  Canvas canvas;
  GraphicsContext gc;
  int x [] = new int [size * size];
  int y [] = new int [size * size];
  Thread game;
  boolean lost = false;
  @Override
  public void start (Stage primaryStage) {
    StackPane root = new StackPane ();
    canvas = new Canvas (size, size);
    gc = canvas.getGraphicsContext2D ();
    canvas.setFocusTraversable (true);
    root.getChildren (). add (canvas);
    startGame ();
    canvas.setOnKeyPressed (new EventHandler & lt; KeyEvent & gt; () {
      @Override
      public void handle (KeyEvent e) {
        KeyCode key = e.getCode ();
        if (key.equals (KeyCode.UP)) dir = up;
        if (key.equals (KeyCode.DOWN)) dir = down;
        if (key.equals (KeyCode.LEFT)) dir = left;
        if (key.equals (KeyCode.RIGHT)) dir = right;
      }
    });
    Scene scene = new Scene (root, size, size);
    primaryStage.setTitle ("Hello World!");
    primaryStage.setScene (scene);
    primaryStage.show ();
  }
  private void draw (GraphicsContext gc) {
    gc.clearRect (0, 0, size, size);
    if (! lost) {
      gc.setFill (Paint.valueOf ("green"));
      gc.fillOval (food_x, food_y, dot_size, dot_size);
      gc.setFill (Paint.valueOf ("red"));
      gc.fillOval (x [0], y [0], dot_size, dot_size);
      gc.setFill (Paint.valueOf ("orange"));
      for (int i = 1; i & lt; length; i ++) {
        gc.fillOval (x [i], y [i], dot_size, dot_size);}
    } else {
      gc.setFill (Paint.valueOf ("black"));
      gc.fillText ("Game Over", size / 2-50, size / 2-15);
      game.stop ();
    }
  }
  / **
   * @param args the command line arguments
   * /
  public static void main (String [] args) {
    launch (args);
  }
  private void startGame () {
    length = 3;
    for (int i = 0; i & lt; length; i ++) {
      x [i] = 50-i * dot_size;
      y [i] = 50;
    }
    locateFood ();
    game = new Thread (new Runnable () {
      @Override
      public void run () {
        while (true) {
          if (! lost) {
            checkFood ();
            checkCollision ();
            move ();
          }
          draw (gc);
          try {
            Thread.sleep (delay);
          } catch (Exception e) {};
        }
      }
    });
    game.start ();
  }
  private void locateFood () {
    food_x = (int) (Math.random () * ((size / dot_size) -1)) * dot_size;
    food_y = (int) (Math.random () * ((size / dot_size) -1)) * dot_size;
  }
  private void checkFood () {
    if (x [0] == food_x & amp; & amp; y [0] == food_y) {
      length ++;
      locateFood ();
    }
  }
  private void checkCollision () {
    if (x [0] & gt; = size) lost = true;
    if (y [0] & gt; = size) lost = true;
    if (x [0] & lt; 0) lost = true;
    if (y [0] & lt; 0) lost = true;
    for (int i = 3; i & lt; length; i ++)
      if (x [0] == x [i] & amp; & amp; y [0] == y [i]) lost = true;
  }
  private void move () {
    for (int i = length-1; i & gt; 0; i -) {
      x [i] = x [i-1];
      y [i] = y [i-1];
    }
    if (dir == up) y [0] - = dot_size;
    if (dir == down) y [0] + = dot_size;
    if (dir == right) x [0] + = dot_size;
    if (dir == left) x [0] - = dot_size;
  }
}

Answer 1, Authority 100%

It seems to me the solution in the forehead:

if (key.equals (keycode.up)) dir = up;
if (key.equals (keycode.down)) dir = down;
if (key.equals (keycode.left)) dir = left;
if (key.equals (keycode.right)) Dir = Right;

In this section of the code, we simply add checks on dir! = down (in case keycode.up ) and so on.