各个功能的实现总的来说就是如下几步：

1. 定义数据

2. 画上去

3. 监听事件（键盘、事件）

   具体代码如下：

   Data.java

   public class Data {
       public static URL bodyUrl = Data.class.getResource("statics/body.png");
       public static ImageIcon body = new ImageIcon(bodyUrl);
       public static URL downUrl = Data.class.getResource("statics/down.png");
       public static ImageIcon down = new ImageIcon(downUrl);
       public static URL foodUrl = Data.class.getResource("statics/food.png");
       public static ImageIcon food = new ImageIcon(foodUrl);
       public static URL headerUrl = Data.class.getResource("statics/header.png");
       public static ImageIcon header = new ImageIcon(headerUrl);
       public static URL leftUrl = Data.class.getResource("statics/left.png");
       public static ImageIcon left = new ImageIcon(leftUrl);
       public static URL rightUrl = Data.class.getResource("statics/right.png");
       public static ImageIcon right = new ImageIcon(rightUrl);
       public static URL upUrl = Data.class.getResource("statics/up.png");
       public static ImageIcon up = new ImageIcon(upUrl);
   }
   
   

   GamePanel.java

   //游戏的面板
   public class GamePanel  extends JPanel implements KeyListener, ActionListener {
       //定义蛇的数据结构
       int length;//蛇的长度
       int[] snakeX = new int[600];//蛇的X坐标 25*25
       int[] snakeY = new int[500];//蛇的Y坐标 25*25
       String fx;
   
       //食物的坐标
       int foodx;
       int foody;
       Random random = new Random();
   
       int score;//成绩
   
   
       //游戏当前的状态:开始/停止
       boolean isStart = false;//默认是不开始
   
       boolean isfail = false;//游戏失败状态
   
       //定时器 以ms为单位 1000ms = 1s
       Timer timer = new Timer(150,this);//100ms执行一次
   
       //构造器
       public GamePanel() {
           init();
           //获得焦点和键盘事件
           this.setFocusable(true);//获得焦点事件
           this.addKeyListener(this);//获得键盘监听事件
           timer.start();//游戏一开始就启动
       }
   
       //初始化方法
       public void init(){
           length = 3;
           snakeX[0] = 100;snakeY[0] = 100;//脑袋的坐标
           snakeX[1] = 75;snakeY[1] = 100;//第一个身体的坐标
           snakeX[2] = 50;snakeY[2] = 100;//第二个身体的坐标
           fx = "R";//初始方向，向右
   
           //把食物随机分布在界面上
           foodx = 25 + 25*random.nextInt(34);
           foody = 75 +25*random.nextInt(24);
   
           score = 0;
   
       }
   
   
   
   
       //绘制画板，所有东西都是用这个画笔来画
       @Override
       protected void paintComponent(Graphics g) {
           super.paintComponent(g);//清屏
   
           //绘制静态的面板
           this.setBackground(Color.WHITE);
           Data.header.paintIcon(this, g, 25, 11);//头部广告栏
           g.fillRect(25,75,850,600);//默认的游戏界面
   
           //把蛇画上去
           if (fx.equals("R")){
               Data.right.paintIcon(this,g,snakeX[0],snakeY[0]);
           }else if(fx.equals("L")){
               Data.left.paintIcon(this,g,snakeX[0],snakeY[0]);
           }else if(fx.equals("U")){
               Data.up.paintIcon(this,g,snakeX[0],snakeY[0]);
           }else if(fx.equals("D")){
               Data.down.paintIcon(this,g,snakeX[0],snakeY[0]);
           }
   
           for (int i = 1; i < length; i++) {
               Data.body.paintIcon(this,g,snakeX[i],snakeY[i]);
           }
   
           //画食物
           Data.food.paintIcon(this,g,foodx,foody);
   
           //画积分
           g.setColor(Color.WHITE);
           g.setFont(new Font("微软雅黑", Font.BOLD, 18));
           g.drawString("长度"+length,750,35);
           g.drawString("分数"+score,750,50);
   
   
           //游戏状态
           if(isStart == false){
               g.setColor(Color.WHITE);
               g.setFont(new Font("微软雅黑", Font.BOLD, 40));
               g.drawString("按下空格开始游戏",300,300);
           }
   
           if(isfail == true){
               g.setColor(Color.RED);
               g.setFont(new Font("微软雅黑", Font.BOLD, 40));
               g.drawString("失败！按下空格重新开始",300,300);
           }
   
       }
   
       //键盘监听事件
       @Override
       public void keyPressed(KeyEvent e) {
           int keyCode = e.getKeyCode();//获得键盘按键是哪一个
           if (keyCode == KeyEvent.VK_SPACE) {//如果按下的是空格键
               if (isfail) {
                   //重新开始
                   isfail = false;
                   init();
               } else {
                   isStart = !isStart;//取反
               }
               repaint();
           }
   
           //小蛇移动
           if (keyCode == KeyEvent.VK_UP) {
               fx = "U";
           } else if (keyCode == KeyEvent.VK_DOWN) {
               fx = "D";
           } else if (keyCode == KeyEvent.VK_LEFT) {
               fx = "L";
           } else if (keyCode == KeyEvent.VK_RIGHT) {
               fx = "R";
   
           }
       }
   
       //事件监听
       @Override
       public void actionPerformed(ActionEvent e) {
           if(isStart && isfail==false){//符合条件就让蛇动起来
               //右移
               for (int i = length-1; i >  0; i--) {
                   snakeX[i] = snakeX[i-1];
                   snakeY[i] = snakeY[i-1];
               }
   
               //走向
               if (fx.equals("R")){
                   snakeX[0] = snakeX[0]+25;
                   if (snakeX[0]>850){ snakeX[0] = 25;}//边界判断
               }else if (fx.equals("L")){
                   snakeX[0] = snakeX[0]-25;
                   if (snakeX[0]<25){ snakeX[0] = 850;}//边界判断
               } else if (fx.equals("U")){
                   snakeY[0] = snakeY[0]-25;
                   if (snakeY[0]<75){ snakeY[0] = 650;}//边界判断
               } else if (fx.equals("D")){
                   snakeY[0] = snakeY[0]+25;
                   if (snakeY[0]>650){ snakeY[0] = 75;}//边界判断
               }
   
               //吃食物
               if(snakeX[0] == foodx && snakeY[0] ==foody){
                   //长度1
                   length++;
                   //分数加10
                   score = score +10;
                   //再次随机食物
                   foodx = 25 + 25*random.nextInt(34);
                   foody = 75 +25*random.nextInt(24);
               }
   
               //失败判断（撞到自己算失败）
               for (int i = 1; i < length; i++) {
                   if (snakeX[0] == snakeX[i] && snakeY[0] == snakeY[i]){
                       isfail = true;
                   }
               }
   
   
               repaint();//重画页面
           }
           timer.start();//定时器开启
       }
   
       @Override
       public void keyTyped(KeyEvent e) {
   
       }
   
   
       @Override
       public void keyReleased(KeyEvent e) {
   
       }
   
   }
   

StartGame.java

//游戏的主启动类
public class StartGame {
    public static void main(String[] args) {
        JFrame frame = new JFrame();
        frame.setBounds(10, 10, 900, 720);
        frame.setResizable(false);
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

        frame.add(new GamePanel());
        frame.setVisible(true);
    }
}

效果图：