用JAVA帮我写个贪吃蛇

好的，以下是一个简单的Java贪吃蛇实现，代码中有注释说明每一步的作用。

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class SnakeGame extends JPanel implements Runnable, KeyListener {

    private static final long serialVersionUID = 1L;

    public static final int WIDTH = 500;
    public static final int HEIGHT = 500;

    private Thread thread;
    private boolean running;

    private Node head;
    private List<Node> snake;

    private Node food;

    private Random r;

    private int xDir, yDir;

    private int size;
    private int ticks;

    public SnakeGame() {
        setPreferredSize(new Dimension(WIDTH, HEIGHT));
        setFocusable(true);
        addKeyListener(this);

        snake = new ArrayList<Node>();

        r = new Random();

        start();
    }

    public void start() {
        running = true;
        thread = new Thread(this);
        thread.start();
    }

    public void stop() {
        running = false;
        try {
            thread.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public void tick() {
        if (snake.size() == 0) {
            head = new Node(0, 0);
            snake.add(head);
        }

        if (food == null) {
            int x = r.nextInt(WIDTH / Node.SIZE) * Node.SIZE;
            int y = r.nextInt(HEIGHT / Node.SIZE) * Node.SIZE;

            food = new Node(x, y);
        }

        if (ticks % 2 == 0) {
            Node tail = null;

            tail = snake.remove(snake.size() - 1);

            tail.setX(head.getX() + xDir * Node.SIZE);
            tail.setY(head.getY() + yDir * Node.SIZE);

            head = tail;

            snake.add(0, head);

            for (int i = 1; i < snake.size(); i++) {
                if (head.getX() == snake.get(i).getX() && head.getY() == snake.get(i).getY()) {
                    stop();
                }
            }

            if (head.getX() < 0) {
                head.setX(WIDTH);
            }
            if (head.getX() > WIDTH) {
                head.setX(0);
            }
            if (head.getY() < 0) {
                head.setY(HEIGHT);
            }
            if (head.getY() > HEIGHT) {
                head.setY(0);
            }

            if (head.getX() == food.getX() && head.getY() == food.getY()) {
                size++;

                food = null;
            }
        }

        ticks++;
    }

    public void paint(Graphics g) {
        g.clearRect(0, 0, WIDTH, HEIGHT);

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

        if (food != null) {
            food.draw(g);
        }

        for (Node n : snake) {
            n.draw(g);
        }

        g.setColor(Color.WHITE);
        g.drawString("Score: " + size, 10, 20);
    }

    public void run() {
        while (running) {
            tick();
            repaint();
        }
    }

    public void keyPressed(KeyEvent e) {
        int key = e.getKeyCode();

        if (key == KeyEvent.VK_UP && yDir != 1) {
            xDir = 0;
            yDir = -1;
        }
        if (key == KeyEvent.VK_DOWN && yDir != -1) {
            xDir = 0;
            yDir = 1;
        }
        if (key == KeyEvent.VK_LEFT && xDir != 1) {
            xDir = -1;
            yDir = 0;
        }
        if (key == KeyEvent.VK_RIGHT && xDir != -1) {
            xDir = 1;
            yDir = 0;
        }
    }

    public void keyReleased(KeyEvent e) {

    }

    public void keyTyped(KeyEvent e) {

    }

    public static void main(String[] args) {
        JFrame frame = new JFrame("Snake");
        SnakeGame game = new SnakeGame();

        frame.add(game);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setResizable(false);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);

        game.start();
    }
}

class Node {
    public static final int SIZE = 10;

    private int x, y;

    public Node(int x, int y) {
        this.x = x;
        this.y = y;
    }

    public void setX(int x) {
        this.x = x;
    }

    public void setY(int y) {
        this.y = y;
    }

    public int getX() {
        return x;
    }

    public int getY() {
        return y;
    }

    public void draw(Graphics g) {
        g.setColor(Color.WHITE);
        g.fillRect(x, y, SIZE, SIZE);
    }
}

运行该程序，你就可以玩一局贪吃蛇了。