JAVA简洁实现贪吃蛇游戏

import java.awt.*; 
  import java.awt.event.*; 
  import javax.swing.*; 
  import java.util.*; 
   
  public class GreedSnake implements KeyListener{ 
   JFrame mainFrame; 
   Canvas paintCanvas; 
   JLabel labelScore; 
   SnakeModel snakeModel = null; 
   
   public static final int canvasWidth = 200; 
   public static final int canvasHeight = 300; 
   
   public static final int nodeWidth = 10; 
   public static final int nodeHeight = 10; 
   
   public GreedSnake() { 
    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; 
    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(); 
   } 
   
   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: 
       snakeModel.changeDirection(SnakeModel.DOWN); 
       break; 
      case KeyEvent.VK_LEFT: