5个小时写一个扑克牌游戏——金钩钓鱼
罗大佑有歌云：“无聊的日子总是会写点无聊的歌曲......”，我不是歌手，我是程序员，于是无聊的日子总是会写点无聊的程序。程序不能太大，不然没有时间完成；程序应该有趣，不然就达不到消磨时间的目的；程序应该有那么一点挑战性，不然即使写完了也没有进步。
金钩钓鱼游戏是我儿时经常玩的一种扑克牌游戏，规则非常简单，两个玩家，一旦牌发到手里之后，接下来每个人出什么牌基本上已经就定了，玩家没有自己做决策的机会，所以这个游戏很容易用程序自动模拟出来。
（一）关于金钩钓鱼游戏
基本规则（简化版）：两个玩家（Player），一副扑克(Deck)，大小王(Joker)可要可不要，我们的游戏假定包含大小王，洗牌(Shuffle)之后，每个玩家得到同样数目的牌（27张），玩家任何时候不能看自己手里的牌，玩家依次出牌，每次出一张，轮到自己出牌时，抽出自己手中最底下的一张牌放到牌桌（Board）上，牌桌上的牌按照玩家出牌的顺序摆成一条长链。J（钩）是最特殊的一张牌，当某个玩家出到J时，便将牌桌上的所有牌都归为己有，并放到自己牌池的最上面（与出牌时恰恰相反），此即所谓“金钩钓鱼”，此时牌桌清空，再由此玩家重新出牌。另外，当自己出的牌与牌桌上的某张牌点数相同时，便将牌桌中那张牌及其之后的牌都归为己有（包含自己刚出的那张），再由此玩家重新出牌，比如牌桌上的牌为3，7，8，4，9，当某个玩家出了8，便将牌桌上的8，4，9连同自己刚出的8一并收回，派桌上剩下3，7。最后，谁手中的牌最先出完，谁就输了。
（二）对于一副牌的建模
由于花色(Suit)对于此游戏并不重要，所以对扑克牌建模时省略了对花色的建模，同样，由于不需要比较大小，牌的点数（Rank）可以用String来表示(其中王用"W"表示)。
Card.java
package com.thoughtworks.davenkin.simplefishinggame;
public class Card {
private String rank;
public Card(String rank) {
this.rank = rank;
}
public String getRank() {
return rank;
}
}
一副扑克（Deck）由54张牌组成：
Deck.java
package com.thoughtworks.davenkin.simplefishinggame;
import java.util.ArrayList;
import java.util.Collections;
public class Deck {
ArrayList<Card> cards = new ArrayList<Card>();
public Deck() {
buildDeck();
}
private void buildDeck() {
buildNumberCards();
buildCard("J");
buildCard("Q");
buildCard("K");
buildCard("A");
buildJokerCard();
}
private void buildJokerCard() {
cards.add(new Card("W"));
cards.add(new Card("W"));
}
private void buildNumberCards() {
for (int rank = 2; rank <= 10; rank++) {
buildCard(rank);
}
}
private void buildCard(int rank) {
for (int index = 1; index <= 4; index++) {
cards.add(new Card(String.valueOf(rank)));
}
}
private void buildCard(String rank) {
for (int index = 1; index <= 4; index++) {
cards.add(new Card(rank));
}
}
public ArrayList<Card> getCards() {
return cards;
}
public void shuffle() {
Collections.shuffle(cards);
}
}
Deck不仅包含54张牌，还定义了洗牌（shuffle）等方法。
（三）对玩家的建模
玩家（Player）有自己的名字和自己手中所剩的牌，最重要的是出牌（playCard）成员方法：
Player.java
package com.thoughtworks.davenkin.simplefishinggame;
import java.util.ArrayList;
import java.util.List;
public class Player {
ArrayList<Card> cards = new ArrayList<Card>();
String name;
public Player(String name) {
this.name = name;
}
public String getName() {
return name;
}
public ArrayList<Card> getCards() {
return cards;
}
public void obtainCards(List<Card> cardsToAdd) {
cards.addAll(cardsToAdd);
}
public void playCard(Board board) {
board.addCard(cards.get(0));
System.out.println(name + " played " + cards.get(0).getRank());
board.displayCards();
cards.remove(0);
}
public void displayCards() {
System.out.print("Cards for " + name + ": ");
for (Card card : cards) {
System.out.print(card.getRank() + " ");
}
System.out.println();
}
}
游戏开始需要发牌，专门定义了一个CardDistributor来发牌，每个玩家得到相同数量的牌。当然，发牌动作应该在洗牌之后：
CardDistributor.java
package com.thoughtworks.davenkin.simplefishinggame;
import java.util.List;
public class CardDistributor {
public void distributeCards(Deck deck, List<Player> players) {
int cardsPerPlayer = deck.getCards().size() / players.size();
int startIndex = 0;
for (Player player : players) {
player.obtainCards(deck.getCards().subList(startIndex, cardsPerPlayer + startIndex));
startIndex += cardsPerPlayer;
}
}
}
玩家在出牌时，需要将自己手中的一张牌转移到牌桌上（Board），而当Player出牌之后，牌桌应该确定是否有将被Player“钓”进的牌，于是在Borad中还定义了getCardsToBeFished方法:
Board.java
package com.thoughtworks.davenkin.simplefishinggame;
import java.util.ArrayList;
import java.util.List;
public class Board {
ArrayList<Card> cards = new ArrayList<Card>();
public ArrayList<Card> getCards() {
return cards;
}
public void addCard(Card card) {
cards.add(card);
}
public List<Card> getCardsToBeFished() {
if (cards.size() == 1)
return null;
List<Card> cardsToBeFished;
Card lastCard = cards.get(cards.size() - 1);
if (lastCard.getRank().equals("J")) {
cardsToBeFished = cards;
} else {
cardsToBeFished = getCardsOfRangeFishing(lastCard);
}
return cardsToBeFished;
}
public void displayCards() {
System.out.print("Current cards on board:");
for (Card card : cards) {
System.out.print(card.getRank() + " ");
}
System.out.println();
}
public void removeFishedCards(List<Card> cardsToBeFished) {
int endIndex = getCards().indexOf(cardsToBeFished.get(0));
ArrayList<Card> newCards = new ArrayList<Card>();
newCards.addAll(cards.subList(0, endIndex));
cards = newCards;
}
private List<Card> getCardsOfRangeFishing(Card lastCard) {
int startIndex = -1;
for (Card card : cards) {
if (card == lastCard)
break;
if (card.getRank().equals(lastCard.getRank())) {
startIndex = cards.indexOf(card);
}
}
if (startIndex != -1)
return cards.subList(startIndex, cards.indexOf(lastCard) + 1);
return null;
}
}
(四) 对整个游戏的建模
整个游戏定义了一个FishingManager来集中管理，FishingManager包括所有玩家，牌桌等成员变量。
FishingManager.java
package com.thoughtworks.davenkin.simplefishinggame;
import java.util.ArrayList;
import java.util.ListIterator;
public class FishingManager implements FishingRuleChecker, AfterPlayListener {
ArrayList<Player> players = new ArrayList<Player>();
private Player currentPlayer;
Board board;
private ListIterator<Player> iterator;
public FishingManager() {
board = new Board();
}
private void resetPlayerIterator() {
iterator = players.listIterator();
}
public void addPlayers(ArrayList<Player> players) {
this.players.addAll(players);
resetPlayerIterator();
}
@Override
public Player nextPlayer() {
if (iterator.hasNext()) {
return iterator.next();
}
resetPlayerIterator();
return nextPlayer();
}
@Override
public Player whoFailed() {
ListIterator<Player> listIterator = players.listIterator();
while (listIterator.hasNext()) {
Player currentPlayer = listIterator.next();
if (currentPlayer.getCards().size() == 0)
return currentPlayer;
}
return null;
}
@Override
public void afterPlay() {
if (board.getCardsToBeFished() == null)
return;
doFish();
nextPlayer();
}
private void doFish() {
System.out.println(currentPlayer.getName() + " fished cards");
currentPlayer.obtainCards(board.getCardsToBeFished());
board.removeFishedCards(board.getCardsToBeFished());
currentPlayer.displayCards();
board.displayCards();
}
public void start() {
int count = 0;
while (true) {
currentPlayer = nextPlayer();
currentPlayer.displayCards();
currentPlayer.playCard(board);
afterPlay();
count++;
if (whoFailed() != null) {
break;
}
}
System.out.println(whoFailed().getName() + " has failed.");
System.out.println("Total: " + count + " rounds");
}
public static void main(String[] args) {
FishingManager manager = new FishingManager();
Player player1 = new Player("Kayla");
Player player2 = new Player("Samuel");
ArrayList<Player> players = new ArrayList<Player>();
players.add(player1);
players.add(player2);
Deck deck = new Deck();
deck.shuffle();
CardDistributor distributor = new CardDistributor();
distributor.distributeCards(deck, players);
manager.addPlayers(players);
manager.start();
}
}
FishingManager还应该包含游戏规则，比如决定输赢和玩家出牌顺序等，于是定义一个游戏规则接口FishingRuleChecker，并使FishingManager实现FishingRuleChecker接口：
FishingRuleChecker.java
package com.thoughtworks.davenkin.simplefishinggame;
public interface FishingRuleChecker {
Player nextPlayer();
Player whoFailed();
}
同时，当每个玩家出牌之后，FishingManager应该决定是否有鱼上钩，并执行钓鱼操作，于是定义了一个AfterPlayListener接口，FishingManager也实现了
AfterPlayListener接口：
AfterPlayListener.java
package com.thoughtworks.davenkin.simplefishinggame;
public interface AfterPlayListener {
public void afterPlay();
}
（五）有趣的现象
运行FinshingManager便可以自动模拟整个游戏过程，笔者比较感兴趣的是：所有玩家一共出多少手牌之后游戏结束？于是笔者做了10000次模拟试验，得到的结果为：最大14023手，最小66手，平均1303手，请数学高手帮忙证明一下是否有个统计学意义上的期望值。出牌次数分布图如下：
上图中，横轴为游戏轮次（一共10000次），纵轴为每次游戏所对应的出牌手数。
