Java贪吃蛇源代码讲解

贪吃蛇是一款较老的经典电子游戏。它最初是在 70 年代后期创建的。后来它被带到了PC上。在这个游戏中，玩家控制一条蛇。目标是尽可能多地吃苹果。蛇每吃一个苹果，它的身体就会变大。蛇必须避开墙壁和自己的身体。这个游戏有时被称为Nibbles。

Java Sname 游戏的开发

蛇的每个关节的大小是 10 像素。蛇是用光标键控制的。最初，这条蛇有三个关节。如果游戏结束，棋盘中央会显示“游戏结束”消息。

package com.zetcode;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import javax.swing.ImageIcon;
import javax.swing.JPanel;
import javax.swing.Timer;
public class Board extends JPanel implements ActionListener {
    private final int B_WIDTH = 300;
    private final int B_HEIGHT = 300;
    private final int DOT_SIZE = 10;
    private final int ALL_DOTS = 900;
    private final int RAND_POS = 29;
    private final int DELAY = 140;
    private final int x[] = new int[ALL_DOTS];
    private final int y[] = new int[ALL_DOTS];
    private int dots;
    private int apple_x;
    private int apple_y;
    private boolean leftDirection = false;
    private boolean rightDirection = true;
    private boolean upDirection = false;
    private boolean downDirection = false;
    private boolean inGame = true;
    private Timer timer;
    private Image ball;
    private Image apple;
    private Image head;
    public Board() {        
        initBoard();
    }    
    private void initBoard() {
        addKeyListener(new TAdapter());
        setBackground(Color.black);
        setFocusable(true);
        setPreferredSize(new Dimension(B_WIDTH, B_HEIGHT));
        loadImages();
        initGame();
    }
    private void loadImages() {
        ImageIcon iid = new ImageIcon("src/resources/dot.png");
        ball = iid.getImage();
        ImageIcon iia = new ImageIcon("src/resources/apple.png");
        apple = iia.getImage();
        ImageIcon iih = new ImageIcon("src/resources/head.png");
        head = iih.getImage();
    }
    private void initGame() {
        dots = 3;
        for (int z = 0; z < dots; z++) {
            x[z] = 50 - z * 10;
            y[z] = 50;
        }       
        locateApple();
        timer = new Timer(DELAY, this);
        timer.start();
    }
    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        doDrawing(g);
    }    
    private void doDrawing(Graphics g) {        
        if (inGame) {
            g.drawImage(apple, apple_x, apple_y, this);
            for (int z = 0; z < dots; z++) {
                if (z == 0) {
                    g.drawImage(head, x[z], y[z], this);
                } else {
                    g.drawImage(ball, x[z], y[z], this);
                }
            }
            Toolkit.getDefaultToolkit().sync();
        } else {
            gameOver(g);
        }        
    }
    private void gameOver(Graphics g) {        
        String msg = "Game Over";
        Font small = new Font("Helvetica", Font.BOLD, 14);
        FontMetrics metr = getFontMetrics(small);
        g.setColor(Color.white);
        g.setFont(small);
        g.drawString(msg, (B_WIDTH - metr.stringWidth(msg)) / 2, B_HEIGHT / 2);
    }
    private void checkApple() {
        if ((x[0] == apple_x) && (y[0] == apple_y)) {
            dots++;
            locateApple();
        }
    }
    private void move() {
        for (int z = dots; z > 0; z--) {
            x[z] = x[(z - 1)];
            y[z] = y[(z - 1)];
        }
        if (leftDirection) {
            x[0] -= DOT_SIZE;
        }
        if (rightDirection) {
            x[0] += DOT_SIZE;
        }
        if (upDirection) {
            y[0] -= DOT_SIZE;
        }
        if (downDirection) {
            y[0] += DOT_SIZE;
        }
    }
    private void checkCollision() {
        for (int z = dots; z > 0; z--) {
            if ((z > 4) && (x[0] == x[z]) && (y[0] == y[z])) {
                inGame = false;
            }
        }
        if (y[0] >= B_HEIGHT) {
            inGame = false;
        }
        if (y[0] < 0) {
            inGame = false;
        }
        if (x[0] >= B_WIDTH) {
            inGame = false;
        }
        if (x[0] < 0) {
            inGame = false;
        }        
        if (!inGame) {
            timer.stop();
        }
    }
    private void locateApple() {
        int r = (int) (Math.random() * RAND_POS);
        apple_x = ((r * DOT_SIZE));
        r = (int) (Math.random() * RAND_POS);
        apple_y = ((r * DOT_SIZE));
    }
    @Override
    public void actionPerformed(ActionEvent e) {
        if (inGame) {
            checkApple();
            checkCollision();
            move();
        }
        repaint();
    }
    private class TAdapter extends KeyAdapter {
        @Override
        public void keyPressed(KeyEvent e) {
            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;
            }
        }
    }
}

首先，我们将定义游戏中使用的常量。

private final int B_WIDTH = 300;
private final int B_HEIGHT = 300;
private final int DOT_SIZE = 10;
private final int ALL_DOTS = 900;
private final int RAND_POS = 29;
private final int DELAY = 140;

B_WIDTH和B_HEIGHT常量决定了板子的大小 。DOT_SIZE是苹果的大小和蛇的圆点。该ALL_DOTS常数定义了板上可能的最大点数 (900 = (300*300)/(10*10))。该RAND_POS 常数用于计算苹果的随机位置。DELAY常数决定了游戏的速度 。

private final int x[] = new int[ALL_DOTS];
private final int y[] = new int[ALL_DOTS];

这两个数组存储蛇所有关节的 x 和 y 坐标。

private void loadImages() {
    ImageIcon iid = new ImageIcon("src/resources/dot.png");
    ball = iid.getImage();
    ImageIcon iia = new ImageIcon("src/resources/apple.png");
    apple = iia.getImage();
    ImageIcon iih = new ImageIcon("src/resources/head.png");
    head = iih.getImage();
}

在该loadImages()方法中，我们获取游戏的图像。该类ImageIcon用于显示 PNG 图像。

private void initGame() {
    dots = 3;
    for (int z = 0; z < dots; z++) {
        x[z] = 50 - z * 10;
        y[z] = 50;
    }
    locateApple();
    timer = new Timer(DELAY, this);
    timer.start();
}

在initGame()我们创建蛇的方法中，在板上随机定位一个苹果，然后启动计时器。

private void checkApple() {
    if ((x[0] == apple_x) && (y[0] == apple_y)) {
        dots++;
        locateApple();
    }
}

如果苹果撞到头部，我们增加蛇的关节数。我们调用locateApple()随机定位新苹果对象的方法。

在move()方法中我们有游戏的关键算法。要理解它，看看蛇是如何移动的。我们控制了蛇的头。我们可以用光标键改变它的方向。其余关节沿链条向上移动一个位置。第二个关节移动到第一个关节的位置，第三个关节移动到第二个关节的位置，依此类推。

for (int z = 点; z > 0; z--) { 
    x[z] = x[(z - 1)]; 
    y[z] = y[(z - 1)]; 
}

此代码将关节沿链向上移动。

if (leftDirection) { 
    x[0] -= DOT_SIZE; 
}

这条线将头部向左移动。

在该checkCollision()方法中，我们确定蛇是撞到自己还是撞到了一堵墙。

for (int z = dots; z > 0; z--) {
    if ((z > 4) && (x[0] == x[z]) && (y[0] == y[z])) {
        inGame = false;
    }
}

如果蛇用头撞到它的一个关节，游戏就结束了。

if (y[0] >= B_HEIGHT) { 
    inGame = false; 
}

如果蛇击中棋盘底部，则游戏结束。

package com.zetcode;
import java.awt.EventQueue;
import javax.swing.JFrame;
public class Snake extends JFrame {
    public Snake() {        
        initUI();
    }    
    private void initUI() {        
        add(new Board());        
        setResizable(false);
        pack();        
        setTitle("Snake");
        setLocationRelativeTo(null);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }    
    public static void main(String[] args) {        
        EventQueue.invokeLater(() -> {
            JFrame ex = new Snake();
            ex.setVisible(true);
        });
    }
}

这是主要课程。

setResizable(false);
pack();

该方法会影响某些平台上容器setResizable()的插图。JFrame因此，在方法之前调用它很重要 pack()。否则，蛇的头部与右边界和下边界的碰撞可能无法正常工作。

这是 Java 中的 Snake 游戏。