public class GreedSnake {
  public static void main(String[] args) {
    SnakeModel model = new SnakeModel(20,30);
    SnakeControl control = new SnakeControl(model);
    SnakeView view = new SnakeView(model,control);
    //添加一个观察者，让view成为model的观察者
    model.addObserver(view);
   
    (new Thread(model)).start();
  }
}

package mvcTest;

//SnakeControl.java
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;


public class SnakeControl implements KeyListener{
  SnakeModel model;

  public SnakeControl(SnakeModel model){
    this.model = model;
  }

  public void keyPressed(KeyEvent e) {
    int keyCode = e.getKeyCode();
    if (model.running){        // 运行状态下，处理的按键
      switch (keyCode) {
        case KeyEvent.VK_UP:
          model.changeDirection(SnakeModel.UP);
          break;
        case KeyEvent.VK_DOWN:
          model.changeDirection(SnakeModel.DOWN);
          break;
        case KeyEvent.VK_LEFT:
          model.changeDirection(SnakeModel.LEFT);
          break;
        case KeyEvent.VK_RIGHT:
          model.changeDirection(SnakeModel.RIGHT);
          break;
        case KeyEvent.VK_ADD:
        case KeyEvent.VK_PAGE_UP:
          model.speedUp();
          break;
        case KeyEvent.VK_SUBTRACT:
        case KeyEvent.VK_PAGE_DOWN:
          model.speedDown();
          break;
        case KeyEvent.VK_SPACE:
        case KeyEvent.VK_P:
          model.changePauseState();
          break;
        default:
      }
    }

    // 任何情况下处理的按键，按键导致重新启动游戏
    if (keyCode == KeyEvent.VK_R ||
        keyCode == KeyEvent.VK_S ||
        keyCode == KeyEvent.VK_ENTER) {
      model.reset();
    }
  }

  public void keyReleased(KeyEvent e) {
  }

  public void keyTyped(KeyEvent e) {
  }
}

package mvcTest;


//SnakeModel.java
import javax.swing.*;
import java.util.Arrays;
import java.util.LinkedList;
import java.util.Observable;
import java.util.Random;


class SnakeModel extends Observable implements Runnable {
  boolean[][] matrix;             // 指示位置上有没蛇体或食物
  LinkedList nodeArray = new LinkedList();  // 蛇体
  Node food;
  int maxX;
  int maxY;
  int direction = 2;             // 蛇运行的方向
  boolean running = false;          // 运行状态

  int timeInterval = 200;           // 时间间隔，毫秒
  double speedChangeRate = 0.75;       // 每次得速度变化率
  boolean paused = false;           // 暂停标志

  int score = 0;               // 得分
  int countMove = 0;             // 吃到食物前移动的次数

  // UP and DOWN should be even
  // RIGHT and LEFT should be odd
  public static final int UP = 2;
  public static final int DOWN = 4;
  public static final int LEFT = 1;
  public static final int RIGHT = 3;

  public SnakeModel( int maxX, int maxY) {
    this.maxX = maxX;
    this.maxY = maxY;

    reset();
  }

  public void reset(){
    direction = SnakeModel.UP;       // 蛇运行的方向
    timeInterval = 200;           // 时间间隔，毫秒
    paused = false;             // 暂停标志
    score = 0;               // 得分
    countMove = 0;             // 吃到食物前移动的次数

    // initial matirx, 全部清0
    matrix = new boolean[maxX][];
    for (int i = 0; i < maxX; ++i) {
      matrix[i] = new boolean[maxY];
      Arrays.fill(matrix[i], false);
    }

    // initial the snake
    // 初始化蛇体，如果横向位置超过20个，长度为10，否则为横向位置的一半
    int initArrayLength = maxX > 20 ? 10 : maxX / 2;
    nodeArray.clear();
    for (int i = 0; i < initArrayLength; ++i) {
      int x = maxX / 2 + i;//maxX被初始化为20
      int y = maxY / 2;  //maxY被初始化为30
      //nodeArray[x,y]: [10,15]-[11,15]-[12，15]~~[20,15]
      //默认的运行方向向上，所以游戏一开始nodeArray就变为：
      //    [10，14]-[10，15]-[11，15]-[12，15]~~[19，15]
      nodeArray.addLast(new Node(x, y));
      matrix[x][y] = true;
    }

    // 创建食物
    food = createFood();
    matrix[food.x][food.y] = true;
  }

  public void changeDirection(int newDirection) {
    // 改变的方向不能与原来方向同向或反向
    if (direction % 2 != newDirection % 2) {
      direction = newDirection;
    }
  }

  
  public boolean moveOn() {
    Node n = (Node) nodeArray.getFirst();
    int x = n.x;
    int y = n.y;

    // 根据方向增减坐标值
    switch (direction) {
      case UP:
        y--;
        break;
      case DOWN:
        y++;
        break;
      case LEFT:
        x--;
        break;
      case RIGHT:
        x++;
        break;
    }

    // 如果新坐标落在有效范围内，则进行处理
    if ((0 <= x && x < maxX) && (0 <= y && y < maxY)) {
    
      if (matrix[x][y]) {    // 如果新坐标的点上有东西（蛇体或者食物）
        if (x == food.x && y == food.y) {    // 吃到食物，成功
          nodeArray.addFirst(food);      // 从蛇头赠长

          // 分数规则，与移动改变方向的次数和速度两个元素有关
          int scoreGet = (10000 - 200 * countMove) / timeInterval;
          score += scoreGet > 0 ? scoreGet : 10;
          countMove = 0;

          food = createFood();        // 创建新的食物
          matrix[food.x][food.y] = true;   // 设置食物所在位置
          return true;
        } else                 // 吃到蛇体自身，失败
          return false;
        
      } else {         // 如果新坐标的点上没有东西（蛇体），移动蛇体
        nodeArray.addFirst(new Node(x, y));
        matrix[x][y] = true;
        n = (Node) nodeArray.removeLast();
        matrix[n.x][n.y] = false;
        countMove++;
        return true;
      }
    }
    return false;                  // 触到边线，失败
  }

  public void run() {
    running = true;
    while (running) {
      try {
        Thread.sleep(timeInterval);
      } catch (Exception e) {
        break;
      }

      if (!paused) {
        if (moveOn()) {
          setChanged();      // Model通知View数据已经更新
          notifyObservers();
        } else {
          JOptionPane.showMessageDialog(null,
              \"you failed\",
              \"Game Over\",
              JOptionPane.INFORMATION_MESSAGE);
          break;
        }
      }
    }
    running = false;
  }

  private Node createFood() {
    int x = 0;
    int y = 0;
    // 随机获取一个有效区域内的与蛇体和食物不重叠的位置
    do {
      Random r = new Random();
      x = r.nextInt(maxX);
      y = r.nextInt(maxY);
    } while (matrix[x][y]);

    return new Node(x, y);
  }

  public void speedUp() {
    timeInterval *= speedChangeRate;
  }

  public void speedDown() {
    timeInterval /= speedChangeRate;
  }

  public void changePauseState() {
    paused = !paused;
  }

  public String toString() {
    String result = \"\";
    for (int i = 0; i < nodeArray.size(); ++i) {
      Node n = (Node) nodeArray.get(i);
      result += \"[\" + n.x + \",\" + n.y + \"]\";
    }
    return result;
  }
}

class Node {
  int x;
  int y;

  Node(int x, int y) {
    this.x = x;
    this.y = y;
  }
}

package mvcTest;

//SnakeView.java
import javax.swing.*;
import java.awt.*;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.Observable;
import java.util.Observer;


public class SnakeView implements Observer {
  SnakeControl control = null;
  SnakeModel model = null;

  JFrame mainFrame;
  Canvas paintCanvas;
  JLabel labelScore;

  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 SnakeView(SnakeModel model, SnakeControl control) {
    this.model = model;
    this.control = control;

    mainFrame = new JFrame(\"GreedSnake\");

    Container cp = mainFrame.getContentPane();

    // 创建顶部的分数显示
    labelScore = new JLabel(\"Score:\");
    cp.add(labelScore, BorderLayout.NORTH);

    // 创建中间的游戏显示区域
    paintCanvas = new Canvas();
    paintCanvas.setSize(canvasWidth + 1, canvasHeight + 1);
    paintCanvas.addKeyListener(control);
    cp.add(paintCanvas, BorderLayout.CENTER);

    // 创建底下的帮助栏
    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(control);
    mainFrame.pack();
    mainFrame.setResizable(false);
    mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    mainFrame.setVisible(true);
  }

  void repaint() {
    Graphics g = paintCanvas.getGraphics();

    //draw background
    g.setColor(Color.WHITE);
    g.fillRect(0, 0, canvasWidth, canvasHeight);

    // draw the snake
    g.setColor(Color.BLACK);
    LinkedList na = model.nodeArray;
    Iterator it = na.iterator();
    while (it.hasNext()) {
      Node n = (Node) it.next();
      drawNode(g, n);
    }

    // draw the food
    g.setColor(Color.RED);
    Node n = model.food;
    drawNode(g, n);

    updateScore();
  }

  private void drawNode(Graphics g, Node n) {
    g.fillRect(n.x * nodeWidth,
        n.y * nodeHeight,
        nodeWidth - 1,
        nodeHeight - 1);
  }

  public void updateScore() {
    String s = \"Score: \" + model.score;
    labelScore.setText(s);
  }

  public void update(Observable o, Object arg) {
    repaint();
  }
}