目录结构：

package snake;

import javax.swing.*;

public class StartGame {
    public static void main(String[] args) {
        JFrame frame = new JFrame("贪吃蛇");

        frame.setBounds(10,10,915,720);
        frame.setResizable(false);//窗口不可变
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);//关闭游戏

        frame.add(new GamePanel());

        frame.setVisible(true);//窗口可见
    }
}

package snake;

import javax.swing.*;
import java.net.URL;
//数据
public class Data {

    public static URL headerURL = Data.class.getResource("/statics/header.jpg");
    public static ImageIcon header = new ImageIcon(headerURL);

    public static URL upURL = Data.class.getResource("/statics/up.png");
    public static URL downURL = Data.class.getResource("/statics/down.png");
    public static URL leftURL = Data.class.getResource("/statics/left.png");
    public static URL rightURL = Data.class.getResource("/statics/right.png");
    public static ImageIcon up = new ImageIcon(upURL);
    public static ImageIcon down = new ImageIcon(downURL);
    public static ImageIcon left = new ImageIcon(leftURL);
    public static ImageIcon right = new ImageIcon(rightURL);

    public static URL foodURL = Data.class.getResource("/statics/food.png");
    public static ImageIcon food = new ImageIcon(foodURL);

    public static URL bodyURL = Data.class.getResource("/statics/body.png");
    public static ImageIcon body = new ImageIcon(bodyURL);

}

package snake;

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.util.Random;

//游戏面板
public class GamePanel extends JPanel implements KeyListener, ActionListener {

    //定义蛇的数据
    int length;
    int[] snakeX = new int[600];//蛇X坐标
    int[] snakeY = new int[500];//蛇Y坐标
    String fx;//上 下 左 右 --- U D L R

    boolean isStart; //游戏是否开始

    Timer timer = new Timer(80,this);//定时器

    //食物
    int foodx;
    int foody;
    Random random = new Random();

    //失败判定
    boolean isFail;

    //积分
    int score;

    //构造器
    public GamePanel() {
        init();
        //获取键盘监听事件
        this.setFocusable(true);
        this.addKeyListener(this);
        timer.start();
    }

    //初始化
    public void init(){
        length = 3;
        snakeX[0] = 100; snakeY[0] = 100;//蛇头
        snakeX[1] = 75; snakeY[1] = 100;//第一节身体
        snakeX[2] = 50; snakeY[2] = 100;//第二节身体
        fx = "R";

        isStart = false;
        isFail = false;
        score = 0;

        foodx = 25 + 25*random.nextInt(34);
        foody = 75 + 25*random.nextInt(24);
    }

    //绘制面板
    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);//清屏
        this.setBackground(Color.white);
        Data.header.paintIcon(this,g,25,11);
        g.fillRect(25,75,850,600);

        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]);
        }

        Data.food.paintIcon(this,g,foodx,foody);

        g.setColor(Color.white);
        g.setFont(new Font("微软雅黑",Font.BOLD,18));
        g.drawString("积分："+score,750,40);

        if (isStart == false){
            g.setColor(Color.white);
            g.setFont(new Font("微软雅黑",Font.BOLD,40));
            g.drawString("按空格开始游戏",300,300);
        }

        if (isFail){
            g.setColor(Color.red);
            g.setFont(new Font("微软雅黑",Font.BOLD,40));
            g.drawString("失败！按空格重新开始",300,300);
        }
    }

    //监听键盘
    @Override
    public void keyPressed(KeyEvent e) {//按下
        int keyCode = e.getKeyCode();
        if (keyCode==KeyEvent.VK_SPACE){
            if (isFail){
                isFail = false;
                init();
            }else {
                isStart = !isStart;//取反
            }
            repaint();//刷新界面
        }

        if (keyCode == KeyEvent.VK_LEFT){
            fx = "L";
        }else if (keyCode == KeyEvent.VK_RIGHT){
            fx = "R";
        }else if (keyCode == KeyEvent.VK_UP) {
            fx = "U";
        }else if (keyCode == KeyEvent.VK_DOWN){
            fx = "D";
        }
    }

    @Override
    public void keyReleased(KeyEvent e) {
        //释放
    }

    @Override
    public void keyTyped(KeyEvent e) {
        //敲击
    }

    //定时器，监听时间
    @Override
    public void actionPerformed(ActionEvent e) {
        if (isStart && isFail == false){
            for (int i = length-1; i > 0; i--) {
                snakeX[i] = snakeX[i-1];
                snakeY[i] = snakeY[i-1];
            }

            if (fx.equals("R")){
                snakeX[0] = snakeX[0] + 25;
                //判断边界
                if(snakeX[0]>850){
                    snakeX[0] = 25;
                }
            }else if (fx.equals("L")){
                snakeX[0] = snakeX[0] - 25;
                //判断边界
                if(snakeX[0]<25){
                    snakeX[0] = 850;
                }
            }else if (fx.equals("U")){
                snakeY[0] = snakeY[0] - 25;
                //判断边界
                if(snakeY[0]<75){
                    snakeY[0] = 650;
                }
            }else if (fx.equals("D")){
                snakeY[0] = snakeY[0] + 25;
                //判断边界
                if(snakeY[0]>650){
                    snakeY[0] = 75;
                }
            }

            if (snakeX[0] == foodx && snakeY[0] == foody){
                length++;
                score++;

                foodx = 25 + 25*random.nextInt(34);
                foody = 75 + 25*random.nextInt(24);
            }

            for (int i = 1; i < length; i++) {
                if (snakeX[0]==snakeX[i] && snakeY[0]==snakeY[i]){
                    isFail = true;
                }
            }

            repaint();
        }
        timer.start();
    }
}