Java贪吃蛇游戏：实现边界碰撞检测和得分系统

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.util.*;

public class test extends JFrame implements ActionListener {
    String name;
    JButton jbn = new JButton('开始');
    D jpn = new D();

    test() {
        Container cn = getContentPane();
        cn.setLayout(new BorderLayout());
        cn.add(jbn, BorderLayout.NORTH);
        cn.add(jpn, BorderLayout.CENTER);
        jbn.addActionListener(this);
        setSize(600, 400);
        setVisible(true);
    }

    public void actionPerformed(ActionEvent e) {
        Thread t1 = new Thread(jpn);
        t1.start();
        jpn.requestFocus(true);
    }

    public static void main(String args[]) {
        new test();
    }
}

class D extends JPanel implements Runnable, KeyListener {
    int x = 10;
    int direction = 0;
    Random r = new Random();
    Vector<Point> v = new Vector<Point>();
    Point food = new Point();

    D() {
        v.add(new Point(20, 10));
        v.add(new Point(20, 10));
        v.add(new Point(20, 10));
        v.add(new Point(20, 10));

        int t = r.nextInt(20);
        food.x = t * 10;
        food.y = t * 10;
        addKeyListener(this);
    }



    public void run() {
        try {
            while (true) {
                for (int i = 0; i < v.size() - 1; i++) {
                    Point p = v.get(i);
                    Point p2 = v.get(i + 1);
                    p.x = p2.x;
                    p.y = p2.y;
                }
                if (direction == 0) {
                    Point p = v.get(v.size() - 1);
                    p.x = p.x + 10;
                    // 撞墙检测以及得分系统
                    if (p.x > 580) {
                        JOptionPane.showMessageDialog(null, '你GG了! 最终得分为 ' + (v.size() - 4));
                        System.exit(0);
                    }
                }
                if (direction == 1) {
                    Point p = v.get(v.size() - 1);
                    p.x = p.x - 10;
                    // 撞墙检测以及得分系统
                    if (p.x < 10) {
                        JOptionPane.showMessageDialog(null, '你GG了! 最终得分为 ' + (v.size() - 4));
                        System.exit(0);
                    }
                }
                if (direction == 2) {
                    Point p = v.get(v.size() - 1);
                    p.y = p.y - 10;
                    // 撞墙检测以及得分系统
                    if (p.y < 10) {
                        JOptionPane.showMessageDialog(null, '你GG了! 最终得分为 ' + (v.size() - 4));
                        System.exit(0);
                    }
                }
                if (direction == 3) {
                    Point p = v.get(v.size() - 1);
                    p.y = p.y + 10;
                    // 撞墙检测以及得分系统
                    if (p.y > 370) {
                        JOptionPane.showMessageDialog(null, '你GG了! 最终得分为 ' + (v.size() - 4));
                        System.exit(0);
                    }
                }

                for (int i = 0; i < v.size() - 1; i++) {
                    Point p = v.get(i);
                    Point p2 = v.get(v.size() - 1);
                    // 撞到身体检测以及得分系统
                    if (p.x == p2.x && p.y == p2.y) {
                        JOptionPane.showMessageDialog(null, '你GG了! 最终得分为 ' + (v.size() - 4));
                        System.exit(0);
                    }
                }

                for (int i = 0; i < v.size(); i++) {
                    Point p = v.get(i);
                    if (p.x == food.x && p.y == food.y) {
                        int t = r.nextInt(20);
                        food.x = t * 10;
                        food.y = t * 10;

                        v.add(new Point(p.x, p.y));
                        break;
                    }
                }
                repaint();
                Thread.sleep(100);
            }
        } catch (Exception e) {

        }
    }

    public void paint(Graphics g) {
        super.paint(g);
        for (int i = 0; i < v.size(); i++) {
            Point p = v.get(i);
            int x = p.x;
            int y = p.y;
            if (i == v.size() - 1) {
                g.setColor(Color.blue);
                g.fillOval(x, y, 9, 9);
            } else {
                g.setColor(Color.black);
                g.fillOval(x, y, 9, 9);
            }
        }

        int x = food.x;
        int y = food.y;
        g.setColor(Color.red);
        g.fillRect(x, y, 9, 9);
    }

    public void keyPressed(KeyEvent e) {
        if (e.getKeyCode() == KeyEvent.VK_UP && direction != 3) {
            direction = 2;
        }//增加不能掉头
        if (e.getKeyCode() == KeyEvent.VK_DOWN && direction != 2) {
            direction = 3;
        }//增加不能掉头
        if (e.getKeyCode() == KeyEvent.VK_LEFT && direction != 0) {
            direction = 1;
        }//增加不能掉头
        if (e.getKeyCode() == KeyEvent.VK_RIGHT && direction != 1) {
            direction = 0;
        }//增加不能掉头
    }

    public void keyReleased(KeyEvent e) {

    }

    public void keyTyped(KeyEvent e) {

    }


}
解释一下这个程序的围墙以及得分系统内容：这个程序中的围墙是指游戏界面的边界，当蛇的头部碰到边界时，游戏结束，弹出得分窗口。得分系统是指在游戏中，每吃到一个食物，蛇的长度增加一节，得分也会相应增加一分。最终得分为蛇的长度减去初始长度（4）。如果蛇撞到了自己的身体，游戏也结束。