生成Jar但无法运行 提示 A java exception has occured解决方法

package snake;import javax.swing.*;import java.awt.*;import java.awt.event.*;import java.util.*;public class Game {    @SuppressWarnings("deprecation")    public static void main(String args[]) {        GameFrame frame = new GameFrame();        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);        frame.setResizable(false);        frame.show();        JOptionPane.showMessageDialog(null, "上,下左,右控制蛇的方向\n回车开始,S暂停");    }}@SuppressWarnings("serial")class GameFrame extends JFrame {    public GameFrame() {        setSize(294, 482);        setTitle("贪吃蛇DEMO");        this.setLocation(360, 100);        Container c = getContentPane();        GamePanel panel = new GamePanel();        c.add(panel, BorderLayout.CENTER);    }}@SuppressWarnings("serial")class GamePanel extends JPanel implements KeyListener {    static int panelWidth = 294;    static int panelHeight = 450;    int rectX = 15;    int rectY = 15;    Snake snake;    Node n;    public GamePanel() {        snake = new Snake(this, panelWidth / rectX, panelHeight / rectY);        setBackground(Color.WHITE);        setSize(panelWidth, panelHeight);        setFocusable(true);        addKeyListener(this);    }    public void paintComponent(Graphics g) {        super.paintComponent(g);        Graphics2D g2 = (Graphics2D) g;        LinkedList list = snake.snakeList;        Iterator it = list.iterator();        g2.setColor(Color.black);        while (it.hasNext()) {            n = (Node) it.next();            drawNode(g2, n);        }        g2.setColor(Color.ORANGE);        Node f = snake.food;        drawNode(g2, f);        snake.drawMap(g2);// 绘制地图    }    public void keyPressed(KeyEvent e) {        int keycode = e.getKeyCode();        if (keycode == KeyEvent.VK_ENTER) {            begin();        } else if (keycode == KeyEvent.VK_UP) {            snake.changeDirection(Snake.up);        } else if (keycode == KeyEvent.VK_DOWN) {            snake.changeDirection(Snake.down);        } else if (keycode == KeyEvent.VK_LEFT) {            snake.changeDirection(Snake.left);        } else if (keycode == KeyEvent.VK_RIGHT) {            snake.changeDirection(Snake.right);        } else if (keycode == KeyEvent.VK_S) {            Snake.run = false;        }    }    public void keyReleased(KeyEvent e) {    }    public void keyTyped(KeyEvent e) {    }    public void drawNode(Graphics2D g, Node n) {        g.fillRect(n.x * rectX, n.y * rectY, rectX - 2, rectY - 2);    }    public void begin() {        Snake.run = true;        SnakeThread thread = new SnakeThread(snake);        thread.start();    }}class Node {    int x;    int y;    public Node(int x, int y) {        this.x = x;        this.y = y;    }}class SnakeThread extends Thread {    Snake snake;    public SnakeThread(Snake s) {        snake = s;    }    public void run() {        Snake.run = true;        while (Snake.run) {            try {                snake.move();                sleep(200);            } catch (InterruptedException e) {            }        }        Snake.run = false;    }}class Snake {    GamePanel panel;    Node food;    boolean[][] all;    public static boolean run;    int maxX;    int maxY;    public static int left = 1;    public static int up = 2;    public static int right = 3;    public static int down = 4;    int direction = 4;    LinkedList snakeList = new LinkedList();    public Snake(GamePanel p, int maxX, int maxY) {        panel = p;        this.maxX = maxX;        this.maxY = maxY;        all = new boolean[maxX][maxY];        for (int i = 0; i < maxX; i++) {            for (int j = 0; j < maxY; j++) {                all[i][j] = false;            }        }        int arrayLength = maxX > 20 ? 10 : maxX / 2;        for (int i = 0; i < arrayLength; i++) {            int x = maxX / 10 + i;            int y = maxY / 10;            snakeList.addFirst(new Node(x, y));            all[x][y] = true;        }        food = createFood();        all[food.x][food.y] = true;    }    // 蛇移动的方法    public void move() {        Node n = (Node) snakeList.getFirst();        int x = n.x;        int y = n.y;        if (direction == 3) {            x++;        } else if (direction == 4) {            y++;        } else if (direction == 1) {            x--;        } else if (direction == 2) {            y--;        }        // 实现对蛇撞到自身的检测        if ((0 <= x && x <= GamePanel.panelWidth / 15 - 1)                && (0 <= y && y <= GamePanel.panelHeight / 15 - 1)) {            if (all[x][y]) {                if (x == food.x && y == food.y) {                    snakeList.addFirst(food);                    food = createFood();                    all[food.x][food.y] = true;                } else {                    JOptionPane.showMessageDialog(null, "你撞到自己了");                    System.exit(0);                }            } else {                snakeList.addFirst(new Node(x, y));                all[x][y] = true;                Node l = (Node) snakeList.getLast();                snakeList.removeLast();                all[l.x][l.y] = false;            }        } else {            JOptionPane.showMessageDialog(null, "越界了,游戏结束");            System.exit(0);        }        panel.repaint();    }    public Node createFood() {        int x = 0;        int y = 0;        do {            Random r = new Random();            x = r.nextInt(maxX - 10);            y = r.nextInt(maxY - 10);        } while (all[x][y]);        return new Node(x, y);    }    // 设置蛇不能回头    public void changeDirection(int newDirection) {        if (direction % 2 != newDirection % 2) {            direction = newDirection;        }    }    public void drawMap(Graphics2D g) {        for (int i = 0; i < maxX; i++) {            for (int j = 0; j < maxY; j++) {                if (all[i][j] == true) {                    g.setColor(Color.red);                    g.fillRect(i, j, 4, 4);                }            }        }    }}