Java实现的经典贪吃蛇游戏

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;
//＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝
//Main Class
//＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝
public class GreedSnake implements KeyListener
{
JFrame mainFrame;
Canvas paintCanvas;
JLabel labelScore;//计分牌
SnakeModel snakeModel=null;// 蛇
public static final int canvasWidth=200;
public static final int canvasHeight=300;
public static final int nodeWidth=10;
public static final int nodeHeight=10;
//----------------------------------------------------------------------
//GreedSnake():初始化游戏界面
//----------------------------------------------------------------------
public GreedSnake()
{
//设置界面元素
mainFrame=new JFrame("GreedSnake");
Container cp=mainFrame.getContentPane();
labelScore=new JLabel("Score:");
cp.add(labelScore,BorderLayout.NORTH);
paintCanvas=new Canvas();
paintCanvas.setSize(canvasWidth+1,canvasHeight+1);
paintCanvas.addKeyListener(this);

cp.add(paintCanvas,BorderLayout.CENTER);
JPanel panelButtom=new JPanel();
panelButtom.setLayout(new BorderLayout());
JLabel labelHelp;// 帮助信息
labelHelp=new JLabel("PageUp, PageDown for speed;",JLabel.CENTER);
panelButtom.add(labelHelp,BorderLayout.NORTH);
labelHelp=new JLabel("ENTER or R or S for start;",JLabel.CENTER);
panelButtom.add(labelHelp,BorderLayout.CENTER);
labelHelp=new JLabel("SPACE or P for pause",JLabel.CENTER);
panelButtom.add(labelHelp,BorderLayout.SOUTH);
cp.add(panelButtom,BorderLayout.SOUTH);
mainFrame.addKeyListener(this);
mainFrame.pack();
mainFrame.setResizable(false);
mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
mainFrame.setVisible(true);
begin();
}
//----------------------------------------------------------------------
//keyPressed():按键检测
//----------------------------------------------------------------------
public void keyPressed(KeyEvent e)
{
int keyCode=e.getKeyCode();
if(snakeModel.running) switch(keyCode)
{
case KeyEvent.VK_UP:
snakeModel.changeDirection(SnakeModel.UP);
break;
case KeyEvent.VK_DOWN: