如何用Java写一个简单的贪吃蛇游戏

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.util.ArrayList;
import java.util.Random;
<p>public class SnakeGame extends JPanel implements ActionListener {
private final int BOARD_WIDTH = 300;
private final int BOARD_HEIGHT = 300;
private final int UNIT_SIZE = 10;
private final int GAME_UNITS = (BOARD_WIDTH <em> BOARD_HEIGHT) / (UNIT_SIZE </em> UNIT_SIZE);
private final int DELAY = 150;</p><pre class='brush:java;toolbar:false;'>private ArrayList<Point> snake;
private Point food;
private char direction = 'R'; // R,L,U,D
private boolean running = true;
private Timer timer;
private Random random;

public SnakeGame() {
    random = new Random();
    this.setPreferredSize(new Dimension(BOARD_WIDTH, BOARD_HEIGHT));
    this.setBackground(Color.BLACK);
    this.setFocusable(true);
    this.addKeyListener(new MyKeyAdapter());

    startGame();
}

public void startGame() {
    snake = new ArrayList<>();
    snake.add(new Point(0, 0));
    snake.add(new Point(-1, 0));
    snake.add(new Point(-2, 0));
    spawnFood();
    timer = new Timer(DELAY, this);
    timer.start();
}

public void paintComponent(Graphics g) {
    super.paintComponent(g);
    draw(g);
}

public void draw(Graphics g) {
    if (running) {
        // 画食物
        g.setColor(Color.RED);
        g.fillOval(food.x * UNIT_SIZE, food.y * UNIT_SIZE, UNIT_SIZE, UNIT_SIZE);

        // 画蛇
        for (Point p : snake) {
            g.setColor(Color.GREEN);
            g.fillRect(p.x * UNIT_SIZE, p.y * UNIT_SIZE, UNIT_SIZE, UNIT_SIZE);
        }
    } else {
        gameOver(g);
    }
}

public void move() {
    Point head = new Point(snake.get(0));

    switch (direction) {
        case 'U': head.y--; break;
        case 'D': head.y++; break;
        case 'L': head.x--; break;
        case 'R': head.x++; break;
    }

    snake.add(0, head);

    if (head.equals(food)) {
        spawnFood();
    } else {
        snake.remove(snake.size() - 1);
    }
}

public void checkFood() {
    // 这个例子中在 move 中处理了
}

public void spawnFood() {
    int x = random.nextInt(BOARD_WIDTH / UNIT_SIZE);
    int y = random.nextInt(BOARD_HEIGHT / UNIT_SIZE);
    food = new Point(x, y);

    // 避免食物出现在蛇身上
    for (Point p : snake) {
        if (p.equals(food)) {
            spawnFood();
        }
    }
}

public void checkCollisions() {
    Point head = snake.get(0);

    // 撞墙
    if (head.x < 0 || head.x >= BOARD_WIDTH / UNIT_SIZE ||
        head.y < 0 || head.y >= BOARD_HEIGHT / UNIT_SIZE) {
        running = false;
    }

    // 撞自己
    for (int i = 1; i < snake.size(); i++) {
        if (head.equals(snake.get(i))) {
            running = false;
        }
    }

    if (!running) {
        timer.stop();
    }
}

public void gameOver(Graphics g) {
    g.setColor(Color.RED);
    g.setFont(new Font("Ink Free", Font.BOLD, 40));
    FontMetrics metrics = getFontMetrics(g.getFont());
    String text = "Game Over";
    g.drawString(text, (BOARD_WIDTH - metrics.stringWidth(text)) / 2, BOARD_HEIGHT / 2);
}

@Override
public void actionPerformed(ActionEvent e) {
    if (running) {
        move();
        checkCollisions();
    }
    repaint();
}

public class MyKeyAdapter extends KeyAdapter {
    @Override
    public void keyPressed(KeyEvent e) {
        switch (e.getKeyCode()) {
            case KeyEvent.VK_LEFT:
                if (direction != 'R') direction = 'L';
                break;
            case KeyEvent.VK_RIGHT:
                if (direction != 'L') direction = 'R';
                break;
            case KeyEvent.VK_UP:
                if (direction != 'D') direction = 'U';
                break;
            case KeyEvent.VK_DOWN:
                if (direction != 'U') direction = 'D';
                break;
        }
    }
}

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

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