问编写Snake游戏，Snake中不能有多个块

EN

import acm.program.*;
import acm.graphics.*;
import acm.util.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.awt.Component.*;
import java.awt.Color.*;

import acm.program.*;
import acm.graphics.*;
import acm.util.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;

import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;

public class Board extends GraphicsProgram 
{
  // constants
  private final int 
    APPLICATION_WIDTH = 300,
    APPLICATION_HEIGHT = 300; // application width and height should be equal

  private final int ALL_DOTS = 900;
  private final int DELAY = 100;

  ArrayList<GRect> snakeJoints = new ArrayList<GRect>();
  private Enemy enemy;
  private int dots, foodX, foodY;
  private int randPos = APPLICATION_WIDTH/10 - 1;
  private int dotSize = APPLICATION_WIDTH/30;
  private boolean right = false;
  private boolean left = false;
  private boolean up = false;
  private boolean down = false;
  private boolean gameOver = false;
  private GImage ball, food;
  private RandomGenerator rand;
  private GLabel gameLost;

  public void init()
  {
    setSize(APPLICATION_WIDTH + 3*dotSize, APPLICATION_HEIGHT + 8*dotSize);
    addKeyListeners();

    rand = new RandomGenerator();

    GRect dot = new GRect(dotSize, dotSize);

    snakeJoints.add(new GRect(dotSize, dotSize));
    snakeJoints.get(0).setFillColor(Color.RED);
    snakeJoints.get(0).setFilled(true);

    food = new GImage("food.png");
    food.setSize(.9 * dotSize, .9 * dotSize);

    setBackground(Color.BLACK);

    newSquare();

    placeFood();

    enemy = new Enemy(dotSize);
    add(enemy);
    enemy.setFillColor(Color.MAGENTA);
    enemy.setFilled(true);
    enemy.setLocation(rand.nextInt(1, randPos - 3)*dotSize, 
                      rand.nextInt(1, randPos - 3)*dotSize);
  }

  public void run() 
  {
    while (!gameOver) 
    {
      oneTimeStep();
      pause(DELAY);
    }
  }

  public void oneTimeStep()
  {
    checkLoseCollision();
    checkFood();
    move();
  }

  public void newSquare() 
  {
    snakeJoints.add(new GRect(dotSize, dotSize));
    snakeJoints.get(0).setFillColor(Color.RED);
    snakeJoints.get(0).setFilled(true);
    add(snakeJoints.get(0), APPLICATION_WIDTH/2, APPLICATION_HEIGHT/2);
  }

  public void placeFood() 
  {
    int i = (int) (Math.random() * randPos);
    foodX = ((i * dotSize));
    i = (int) (Math.random() * randPos);
    foodY = ((i * dotSize));
    add(food, foodX - dotSize, foodY - dotSize);
  }

  public void gameLost() 
  {
    gameOver = true;
    gameLost = new GLabel("Game Over", APPLICATION_WIDTH/2, 
                          APPLICATION_HEIGHT/2);
    gameLost.setColor(Color.BLUE);
    add(gameLost);
  }

  public void checkFood() 
  {
    if (snakeJoints.get(0).getBounds().intersects(food.getBounds())) 
    {
      remove(food);
      newSquare();
      placeFood();
    }
  }

  public void move()
  {
    for (int i = snakeJoints.size()-1; i > 0; i--)
    {
      snakeJoints.get(i).setLocation(snakeJoints.get(i-1).getX(), snakeJoints.get(i-1).getY());
    }

    if (left)
    {
      snakeJoints.get(0).move(-dotSize, 0);
    }

    if (right)
    {
      snakeJoints.get(0).move(dotSize, 0);
    }

    if (up) 
    {
      snakeJoints.get(0).move(0, -dotSize);
    }

    if (down) 
    {
      snakeJoints.get(0).move(0, dotSize);
    }
  }

  public void checkLoseCollision() 
  {
    for (int i = dots; i > 0; i--) 
    {
      if ((i > 4) && (snakeJoints.get(0).getBounds().intersects
                        (snakeJoints.get(i).getBounds()))) 
      {
        gameLost();
      }
    }

    if (snakeJoints.get(0).getY() + dotSize > APPLICATION_HEIGHT || snakeJoints.get(0).getY() < 0)
    {
      gameLost();
    }

    if (snakeJoints.get(0).getX() + dotSize > APPLICATION_WIDTH || snakeJoints.get(0).getX() < 0)
    {
      gameLost();
    }

    if (snakeJoints.get(0).getBounds().intersects(enemy.getBounds()))
    {
      gameLost();
    }
  }

  public void keyPressed(KeyEvent e)
  {
    int key = e.getKeyCode();

    if (key == KeyEvent.VK_LEFT)
    {
      left = true;
      right = false;
      up = false;
      down = false;
    }

    if (key == KeyEvent.VK_RIGHT)
    {
      right = true;
      left = false;
      up = false;
      down = false;
    }

    if (key == KeyEvent.VK_UP)
    {
      up = true;
      down = false;
      right = false;
      left = false;
    }

    if (key == KeyEvent.VK_DOWN)
    {
      down = true;
      up = false;
      right = false;
      left = false;
    }
  }
}