public class Game { private static final String[] suits = {"♥","♣","♦","♠"}; public List buyPoker() { List<Poker> pokers = new ArrayList<>(); for (int i = 0; i < 4; i++) { for (int j = 0; j <= 13; j++) { Poker poker = new Poker(suits[i],j); pokers.add(poker); } } return pokers; } public void shuffle(List<Poker> pokers) { for (int i = pokers.size()-1; i > 0; i--) { Random random = new Random(); int index = random.nextInt(i); swap(pokers,i,index); } } private void swap(List<Poker> pokers,int i,int j) { Poker tmp = pokers.get(i); pokers.set(i,pokers.get(j)); pokers.set(j,tmp); } public List<List<Poker>> game(List<Poker> pokers) { List<List<Poker>> hand = new ArrayList<>(); List<Poker> hand1 = new ArrayList<>(); List<Poker> hand2 = new ArrayList<>(); List<Poker> hand3 = new ArrayList<>(); for (int i = 0; i < 3; i++) { for (int j = 0; j < 3; j++) { Poker removePoker = pokers.remove(0); hand.get(j).add(removePoker); } } return hand; } }有错吗

在game方法中，你创建了一个空的List<List<Poker>> hand，但没有将任何元素添加到它中。因此，在尝试将元素添加到hand.get(j)时，会抛出NullPointerException异常。为了解决这个问题，你需要在game方法中为hand添加3个空列表，然后才能向它们中添加元素。

你需要将game方法中的代码修改如下：

public List<List<Poker>> game(List<Poker> pokers) { 
    List<List<Poker>> hand = new ArrayList<>();
    List<Poker> hand1 = new ArrayList<>();
    List<Poker> hand2 = new ArrayList<>();
    List<Poker> hand3 = new ArrayList<>();

    hand.add(hand1);
    hand.add(hand2);
    hand.add(hand3);

    for (int i = 0; i < 3; i++) {
        for (int j = 0; j < 3; j++) {
            Poker removePoker = pokers.remove(0);
            hand.get(j).add(removePoker);
        }
    }

    return hand;
}

这样就能成功地将元素添加到hand中了。

相关问题

import java.util.ArrayList; import java.util.Collections; import java.util.HashMap; import java.util.List; public class PokerGame { public static void main(String[] args) { List<String> pokerCards = new ArrayList<>(); List<String> players = new ArrayList<>(); HashMap<String, List<String>> playerHands = new HashMap<>(); // Step 1: Combine the cards into a deck String[] suits = {"♠", "♥", "♣", "♦"}; String[] ranks = {"A", "2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K"}; for (String suit : suits) { for (String rank : ranks) { pokerCards.add(suit + rank); } } pokerCards.add("小王"); pokerCards.add("大王"); // Step 2: Shuffle the deck Collections.shuffle(pokerCards); // Step 3: Distribute cards to players players.add("小王"); players.add("小李"); players.add("小明"); int numPlayers = players.size(); int cardsPerPlayer = pokerCards.size() / numPlayers; int remainingCards = pokerCards.size() % numPlayers; int cardIndex = 0; for (String player : players) { List<String> hand = new ArrayList<>(); for (int i = 0; i < cardsPerPlayer; i++) { hand.add(pokerCards.get(cardIndex)); cardIndex++; } if (remainingCards > 0) { hand.add(pokerCards.get(cardIndex)); cardIndex++; remainingCards--; } playerHands.put(player, hand); } // Step 4: Display each player's hand for (String player : players) { System.out.println(player + "的手牌：" + playerHands.get(player)); } } }解释这串代码

这段代码是一个简单的扑克牌游戏的实现。以下是对代码的解释：

1. 创建了一个名为PokerGame的类，其中包含了一个main方法作为程序的入口点。

2. 创建了两个ArrayList对象，pokerCards和players，分别用于存储扑克牌和玩家信息。

3. 创建了一个HashMap对象playerHands，用于存储每个玩家的手牌。

4. 使用两个String数组suits和ranks来表示扑克牌的花色和点数。

5. 使用嵌套的for循环将每个花色和点数组合在一起，构成一副完整的扑克牌，并将其添加到pokerCards中。

6. 添加了两张大小王到pokerCards中。

7. 使用Collections.shuffle方法对pokerCards进行洗牌，打乱顺序。

8. 添加了三个玩家到players中。

9. 计算每个玩家应该分到的牌数和剩余的牌数。

10. 使用另一个for循环将牌发给每个玩家，先将牌添加到hand中，再将hand添加到playerHands中。

11. 如果还有剩余的牌，则将剩余的牌发给最后一个玩家。

12. 最后，使用for循环遍历每个玩家，打印出他们的手牌。

这段代码实现了一个简单的扑克牌游戏，包括洗牌和发牌的过程，并将每个玩家的手牌打印出来。

import java.util.ArrayList; import java.util.Collections; import java.util.HashMap; import java.util.List; public class PokeGame { public static void main(String[] args) { List<String> pokerCards = new ArrayList<>(); List<String> players = new ArrayList<>(); HashMap<String, List<String>> playerHands = new HashMap<>(); //创建了两个ArrayList对象，pokerCards和players，分别用于存储扑克牌和玩家信息。 //创建了一个HashMap对象playerHands，用于存储每个玩家的手牌。 String[] suits = {"♠", "♥", "♣", "♦"}; String[] ranks = {"A", "2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K"}; //使用两个String数组suits和ranks来表示扑克牌的花色和点数。 for (String suit : suits) { for (String rank : ranks) { pokerCards.add(suit + rank); } } //使用嵌套的for循环将每个花色和点数组合在一起，构成一副完整的扑克牌，并将其添加到pokerCards中。 pokerCards.add("小王"); pokerCards.add("大王"); //添加了两张大小王到pokerCards中。 Collections.shuffle(pokerCards); //使用Collections.shuffle方法对pokerCards进行洗牌，打乱顺序。 players.add("小王"); players.add("小李"); players.add("小明"); //添加了三个玩家到players中。 int numPlayers = players.size(); int cardsPerPlayer = pokerCards.size() / numPlayers; int remainingCards = pokerCards.size() % numPlayers; //计算每个玩家应该分到的牌数和剩余的牌数。 int cardIndex = 0; for (String player : players) { List<String> hand = new ArrayList<>(); for (int i = 0; i < cardsPerPlayer; i++) { hand.add(pokerCards.get(cardIndex)); cardIndex++; } if (remainingCards > 0) { hand.add(pokerCards.get(cardIndex)); cardIndex++; remainingCards--; } playerHands.put(player, hand); } // Step 4: Display each player's hand for (String player : players) { System.out.println(player + "的手牌：" + playerHands.get(player)); } } } 改成用随机数组洗牌而不是用shuffle方法

要用随机数组洗牌的话，可以使用Fisher-Yates算法。以下是将代码改为使用随机数组洗牌的示例：

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Random;

public class PokeGame {
    public static void main(String[] args) {
        List<String> pokerCards = new ArrayList<>();
        List<String> players = new ArrayList<>();
        HashMap<String, List<String>> playerHands = new HashMap<>();

        String[] suits = {"♠", "♥", "♣", "♦"};
        String[] ranks = {"A", "2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K"};

        for (String suit : suits) {
            for (String rank : ranks) {
                pokerCards.add(suit + rank);
            }
        }
        pokerCards.add("小王");
        pokerCards.add("大王");

        shuffleCards(pokerCards);

        players.add("小王");
        players.add("小李");
        players.add("小明");

        int numPlayers = players.size();
        int cardsPerPlayer = pokerCards.size() / numPlayers;
        int remainingCards = pokerCards.size() % numPlayers;

        int cardIndex = 0;
        for (String player : players) {
            List<String> hand = new ArrayList<>();

            for (int i = 0; i < cardsPerPlayer; i++) {
                hand.add(pokerCards.get(cardIndex));
                cardIndex++;
            }

            if (remainingCards > 0) {
                hand.add(pokerCards.get(cardIndex));
                cardIndex++;
                remainingCards--;
            }

            playerHands.put(player, hand);
        }

        for (String player : players) {
            System.out.println(player + "的手牌：" + playerHands.get(player));
        }
    }

    public static void shuffleCards(List<String> cards) {
        Random random = new Random();
        int size = cards.size();

        for (int i = size - 1; i > 0; i--) {
            int j = random.nextInt(i + 1);
            String temp = cards.get(i);
            cards.set(i, cards.get(j));
            cards.set(j, temp);
        }
    }
}

这里新增了一个`shuffleCards`方法，使用Fisher-Yates算法实现洗牌功能。在洗牌前将扑克牌存储在列表中，然后调用`shuffleCards`方法进行洗牌。最后输出每个玩家的手牌。

希望对你有所帮助！如有任何疑问，请随时提问。