Java Issue计算BlackJack程序中玩家手的值

Question

I want to make a BlackJack game in Java. I'm using arrays to represent the cards. I'm having a problem of getting the card value and using the card values each player has to calculate the hand of each player. I have four classes, Card, Player, Dealer, and BlackJackGame - the driver. I'll post Card with its relevant Value method, Player, and BlackJackGame as dealer is pretty identical to Player.

// 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);

Output

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

You've only added two cards to player3's deck[] , so when you call public int getCardValue(2) it goes to the 3rd index of player3's deck, which is null.

    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;
    }

Other Things...

Instead of each player having an array called deck perhaps rename it to hand and use an ArrayList instead of an array , the ArrayList would allow you to add elements dynamically.

I would use a switch statement in your Card.Value() method. Like so:

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

Your shuffling algorithm is almost correct.

    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.
    }

It should look like this:

    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;
    }

What could I do for the getValue method to calculate the hand? Using the array you have with cCount you could have a method to calculate the hand total:

  public int calcHandTotal() {
      int total = 0;

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

      return total;
  }