Java实现一个贪吃蛇小游戏代码并加注释

以下是Java实现贪吃蛇小游戏的代码，已加上注释：

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

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

public class SnakeGame extends JPanel implements ActionListener, KeyListener {
    // 定义游戏界面大小
    public static final int WIDTH = 500;
    public static final int HEIGHT = 500;

    // 定义蛇的大小
    public static final int DOT_SIZE = 10;

    // 定义蛇的最大长度
    public static final int MAX_DOTS = (WIDTH * HEIGHT) / (DOT_SIZE * DOT_SIZE);

    // 定义游戏的速度
    public static final int DELAY = 140;

    // 定义蛇的身体和食物的坐标
    private ArrayList<Point> snake;
    private Point food;

    // 定义方向
    private boolean leftDirection = false;
    private boolean rightDirection = true;
    private boolean upDirection = false;
    private boolean downDirection = false;

    // 定义游戏是否结束
    private boolean inGame = true;

    // 定义定时器
    private Timer timer;

    public SnakeGame() {
        // 设置游戏界面大小
        setPreferredSize(new Dimension(WIDTH, HEIGHT));

        // 初始化蛇的身体和食物的坐标
        snake = new ArrayList<Point>();
        snake.add(new Point(50, 50));
        snake.add(new Point(40, 50));
        snake.add(new Point(30, 50));

        // 生成随机食物的坐标
        generateFood();

        // 创建定时器
        timer = new Timer(DELAY, this);
        timer.start();

        // 添加键盘监听器
        addKeyListener(this);
        setFocusable(true);
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);

        // 如果游戏还没有结束
        if (inGame) {
            // 绘制食物
            g.setColor(Color.RED);
            g.fillRect(food.x, food.y, DOT_SIZE, DOT_SIZE);

            // 绘制蛇的身体
            for (int i = 0; i < snake.size(); i++) {
                g.setColor(Color.GREEN);
                g.fillRect(snake.get(i).x, snake.get(i).y, DOT_SIZE, DOT_SIZE);
            }
        } else {
            // 如果游戏结束，显示游戏结束
            String msg = "Game Over";
            g.setColor(Color.RED);
            g.drawString(msg, (WIDTH - g.getFontMetrics().stringWidth(msg)) / 2, HEIGHT / 2);
        }
    }

    public void checkFood() {
        // 如果蛇头的坐标和食物的坐标重合
        if (snake.get(0).x == food.x && snake.get(0).y == food.y) {
            // 在蛇的最后添加一个身体
            snake.add(new Point(snake.get(snake.size() - 1)));
            generateFood(); // 生成新的食物
        }
    }

    public void checkCollision() {
        // 如果蛇头碰到边界，游戏结束
        if (snake.get(0).x < 0 || snake.get(0).x > WIDTH - DOT_SIZE || snake.get(0).y < 0
                || snake.get(0).y > HEIGHT - DOT_SIZE) {
            inGame = false;
        }

        // 如果蛇头碰到身体，游戏结束
        for (int i = 1; i < snake.size(); i++) {
            if (snake.get(0).x == snake.get(i).x && snake.get(0).y == snake.get(i).y) {
                inGame = false;
            }
        }
    }

    public void generateFood() {
        // 生成随机食物的坐标
        Random rand = new Random();
        int x = rand.nextInt(WIDTH / DOT_SIZE) * DOT_SIZE;
        int y = rand.nextInt(HEIGHT / DOT_SIZE) * DOT_SIZE;
        food = new Point(x, y);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        // 如果游戏还没有结束
        if (inGame) {
            // 移动蛇的身体
            for (int i = snake.size() - 1; i > 0; i--) {
                snake.set(i, new Point(snake.get(i - 1)));
            }

            // 根据方向移动蛇头
            if (leftDirection) {
                snake.get(0).x -= DOT_SIZE;
            }
            if (rightDirection) {
                snake.get(0).x += DOT_SIZE;
            }
            if (upDirection) {
                snake.get(0).y -= DOT_SIZE;
            }
            if (downDirection) {
                snake.get(0).y += DOT_SIZE;
            }

            // 检查蛇头是否吃到食物
            checkFood();

            // 检查蛇头是否碰到边界或身体
            checkCollision();

            // 重绘游戏界面
            repaint();
        }
    }

    @Override
    public void keyPressed(KeyEvent e) {
        // 根据按键修改方向
        int key = e.getKeyCode();
        if ((key == KeyEvent.VK_LEFT) && (!rightDirection)) {
            leftDirection = true;
            upDirection = false;
            downDirection = false;
        }

        if ((key == KeyEvent.VK_RIGHT) && (!leftDirection)) {
            rightDirection = true;
            upDirection = false;
            downDirection = false;
        }

        if ((key == KeyEvent.VK_UP) && (!downDirection)) {
            upDirection = true;
            rightDirection = false;
            leftDirection = false;
        }

        if ((key == KeyEvent.VK_DOWN) && (!upDirection)) {
            downDirection = true;
            rightDirection = false;
            leftDirection = false;
        }
    }

    @Override
    public void keyReleased(KeyEvent e) {
    }

    @Override
    public void keyTyped(KeyEvent e) {
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame("Snake Game");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setResizable(false);

        SnakeGame game = new SnakeGame();
        frame.add(game);

        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
}