Java问题在BlackJack程序中计算玩家手牌的价值

Question

我想用 Java 制作 BlackJack 游戏。我正在使用数组来表示卡片。我在获取卡值和使用每个玩家必须计算每个玩家的手牌的卡值时遇到问题。我有四个班级，Card、Player、Dealer 和 BlackJackGame——司机。我将发布 Card 及其相关的 Value 方法、Player 和 BlackJackGame，因为庄家与 Player 完全相同。

// Card.Java

public class Card
{
    private String suit, rank; 
    private int value;


    public Card(String suit, String rank)
    {
        this.suit = suit;
        this.rank = rank;
    }

    public String getRank()
    {
        return rank;
    }

    public int Value()
    {
        if(rank.equals("2"))
        {
            value=2;
        }
        else if(rank.equals("3"))
        {
            value=3;
        }
        else if(rank.equals("4"))
        {
            value=4;
        }
        else if(rank.equals("5"))
        {
            value=5;
        }
        else if(rank.equals("6"))
        {
            value=6;
        }
        else if(rank.equals("7"))
        {
            value=7;
        }
        else if(rank.equals("8"))
        {
            value=8;
        }
        else if(rank.equals("9"))
        {
            value=9;
        }
        else if(rank.equals("10"))
        {
            value=10;
        }
        else if(rank.equals("A"))
        {
            value=11;
        }
        else if(rank.equals("Q"))
        {
            value=10;
        }
        else if(rank.equals("J"))
        {
            value=10;
        }
        else if(rank.equals("K"))
        {
            value=10;
        }

        return value;
    }



    public String toString()
    {
        return(rank + " of " + suit);
    }

}

// Player.java

//Player.java

public class Player
{
    private int cValue; // [Card Value] I use this in a method to equal what deck[int] produces and try to use in the getValue method to no avail
    private int cCount; //Card count used to count how many 'cards' added
    Card[] deck= new Card[52]; // 52 card objects
    private int sum; A temporary int I add the cValues into and assign the value to cValue and return it

    public Player()
    {
        cCount=0;

    }

    public void addCard(Card a) //Everytime addCard is executed so I know how many cards are drawn at this point in the program everyone( 3 players and a dealer) has two cards
    {
        deck[cCount] = a;
        cCount++;

    }

    public int getcCount()  //Get the card count from the void method
    {
        return cCount;
    }

    public Card getCard(int a) //Return the deck integer each player has
    {
        return deck[a];
    }

    public int getCardValue(int a) // This works and it produces the value of the card I give the int of the method too however if I use more than two of these in succession, I get a null pointer exception, can't figure it out.  
    {
        cValue = deck[a].Value();
        return cValue;
    }

   public void getValue(int a) //The method I can't get to work, trying to calculate the hand of the player( 
   {
        for(int i =0; i<deck.length; i++)
        {
            sum += cValue;
        }


   }

   public int getValue() // I want to make this the method where the values are summed and return but for some reason no matter what I do I get 0 returned, tried everything.. I really need help with this method.
   {
        cValue = sum;
        return cValue;
   }



}

//BlackJackGame.java

public class BlackJackGame
{



    public static void main(String []   args)
    {
        Card[] deck = new Card[52];
        Player[] player = new Player[3];
        int loopcount=0;

        String[] suit = {"Hearts", "Clubs", "Spades", "Diamonds"};
        String[] rank = {"2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K", "A"};

        for(int i=0; i<13; i++)
        {
            for(int x=0; x<4;x++)
            {
                deck[loopcount] = new Card(suit[x], rank[i]);
                loopcount++;
            }
        }

        System.out.println("Shuffling...");

        for(int i=0; i< deck.length; i++) //Shuffle
        {
            int count= (int)(Math.random()* deck.length);
            deck[i] = deck[count];

        }

        Player player1 = new Player();
        Player player2 = new Player();
        Player player3 = new Player();

        System.out.println("Welcome to our BlackJackGame!");

        System.out.println("Welcome Dealer!");

        Dealer dealer = new Dealer();

        System.out.println("Let's deal the cards!");

        player1.addCard(deck[0]);

        player2.addCard(deck[1]);

        player3.addCard(deck[2]);

    //  System.out.println("Player 1 has: " +deck[0]);

    //  System.out.println("Player 2 has: " +deck[1]);

    //  System.out.println("Player 3 has : " +deck[2]);

    System.out.println("And now the Dealer gets his card...");

        dealer.addCard(deck[3]);

    //  System.out.println("The Dealer has: " +deck[3]);

    System.out.println("Now we get our second cards!");

    System.out.println("Okay Dealer, deal out the cards!");

        player1.addCard(deck[4]);

        player2.addCard(deck[5]);

        player3.addCard(deck[6]);

        dealer.addCard(deck[7]);

        System.out.println("These are the cards player1 has: " +deck[0]+ " "+deck[4]);

        System.out.println("These are the cards player2 has: " +deck[1]+ " "+deck[5]);

        System.out.println("These are the cards player3 has: " +deck[2]+ " "+deck[6]);

        int p1 = player1.getCardValue(0); 
        int p2 = player2.getCardValue(1);
        int p3 = player3.getCardValue(2); // This points to null, why?!

        System.out.println(p1);
        System.out.println(p2);

输出

Shuffling...
*Some print lines of stuff I wrote*
These are the cards this player has: ...  ... 
Exception in thread "main" java.lang.NullPointerException
at Player.getCardValue(Player:java:39)
at BlackJackGame.main(BlackJackGame.java:85)

Answer 1

您只在 player3 的 deck[] 中添加了两张牌，所以当您调用 public int getCardValue(2) 时，它会转到 player3 牌组的第 3 个索引，该索引为空。

    Player player3 = new Player();
    ...
    player3.addCard(deck[2]);
    // deck[0]
    ...
    player3.addCard(deck[6]);
    // deck[1]
    ...
    int p3 = player3.getCardValue(2);
    // get value at deck[2]

    // this goes to ->
    public int getCardValue(int a)  
    {
        // try to access deck[2], but deck only has 
        // 2 valid entries deck[0] and deck[1]
        cValue = deck[a].Value();
        return cValue;
    }

其他事情...

不是每个玩家都有一个名为deck 的数组，或许可以将其重命名为hand 并使用ArrayList 而不是array，ArrayList 将允许您动态添加元素。

我会在您的Card.Value() 方法中使用switch 语句。像这样：

public int Value()
{
    switch(rank) {
    case "A":
        return 11;
    case "K":
    case "Q":
    case "J":
        return 10;
    default:
        return Integer.parseInt(rank);
}

你的洗牌算法几乎是正确的。

    for(int i=0; i< deck.length; i++) //Shuffle
    {
        // this line chooses a random card in the deck
        int count= (int)(Math.random()* deck.length); 
        // this line sets the card at index 'i' to the randomly chosen card
        deck[i] = deck[count];
        // however your creating multiple instance of one card in the deck
        // instead of switching the cards around, this will lead to your deck
        // having more than one of the same card.
    }

应该是这样的：

    for(int i=0; i< deck.length; i++) //Shuffle
    {
        // create a temporary card to hold the value of the card to switch
        Card tmp = deck[i];
        // now choose a random card in the deck
        int count= (int)(Math.random()* deck.length); 
        // now set the card at index 'i' to the randomly chosen card
        deck[i] = deck[count];
        // and set the randomly chosen card to deck[i]
        deck[count] = tmp;
    }

getValue 方法可以做什么来计算手牌？ 使用cCount 的数组，您可以有一种方法来计算手牌总数：

  public int calcHandTotal() {
      int total = 0;

      for(int i = 0; i < cCount; i++) {
          total += deck[i].Value();
      }

      return total;
  }