画板

import javax.swing.*;

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);

        //游戏写在面板上
        frame.add(new GamePanel());
        frame.setVisible(true);
    }
}

游戏面板

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 {

    //定义蛇的数据结构
    int length;
    int[] snakeX = new int[600];
    int[] snakeY = new int[600];
    String fx;//方向

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

    //游戏状态
    boolean isStart = false;
    boolean isFail = false;

    //定时器
    Timer timer = new Timer(100,this);

    //构造器
    public GamePanel() {
        init();
        //获取焦点和键盘事件
        this.setFocusable(true);
        this.addKeyListener(this);
        timer.start();
    }

    //初始化方法
    public void init(){
        length = 3;
        snakeX[0]=100;snakeY[0]=100;
        snakeX[1]=75;snakeY[1]=100;
        snakeX[2]=50;snakeY[2]=100;
        fx = "R";
        foodx = 25+25*random.nextInt(34);
        foody = 75+25*random.nextInt(24);

        score = 0;
    }

    //绘制面板
    @Override
    protected void paintComponent(Graphics g) {

        super.paintComponent(g);//清屏
        //画静态图片
        this.setBackground(Color.white);
        Data.header.paintIcon(this,g,25,11);
        g.fillRect(25,75,850,600);

        //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);

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

        //画小蛇 头 方向
        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 {
            Data.down.paintIcon(this,g,snakeX[0],snakeY[0]);
        }

        //身体
        for (int i = 1; i < length; i++) {
            Data.body.paintIcon(this,g,snakeX[i],snakeY[i]);
        }

        //游戏状态
        if (!isStart){
            g.setColor(Color.white);
            //设置字体
            g.setFont(new Font("微软雅黑",Font.BOLD,40));
            g.drawString("按下空格开始游戏",300,350);

        }

        if (isFail){
            g.setColor(Color.RED);
            //设置字体
            g.setFont(new Font("微软雅黑",Font.BOLD,40));
            g.drawString("失败，按下空格重新开始",300,350);

        }
    }

    //键盘监听事件
    @Override
    public void keyPressed(KeyEvent e) {
        //开始结束
        int keyCode = e.getKeyCode();
        if (keyCode==KeyEvent.VK_SPACE){
            if (isFail){
                isFail = false;
                init();
            } else {
                isStart = !isStart;
            }
            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 {
            fx = "R";
        }
    }

    //事件监听
    @Override
    public void actionPerformed(ActionEvent e) {
        if (isStart && !isFail){
            //吃食物
            if (snakeX[0]==foodx&&snakeY[0]==foody){
                //长度+1
                length++;
                //分数+10
                score+=10;
                //再次随机食物
                foodx = 25+25*random.nextInt(34);
                foody = 75+25*random.nextInt(24);
            }

            //移动身体
            for (int i = length-1; i >0 ; i--) {
                snakeX[i]=snakeX[i-1];
                snakeY[i]=snakeY[i-1];
            }

            //判断走向
            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 {
                snakeY[0]=snakeY[0]+25;
                if (snakeY[0]>650){snakeY[0]=75;}//边界判断
            }

            //失败判断，撞到自己
            for (int i = 1; i < length; i++) {
                if(snakeX[0]==snakeX[i]&&snakeY[0]==snakeY[i])
                    isFail=true;
            }
            repaint();
        }
        timer.start();
    }


    @Override
    public void keyReleased(KeyEvent e) {

    }

    @Override
    public void keyTyped(KeyEvent e) {

    }
}

数据

import javax.swing.*;
import java.net.URL;

// 数据中心
public class Data {

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

}

效果