我想用Java制作BlackJack游戏。我正在使用数组代表卡片。我有一个问题是获得卡值并使用卡值，每个玩家必须计算每个玩家的牌。我有四个课程，卡片，播放器，经销商和BlackJackGame - 驱动程序。我将使用其相关的Value方法，Player和BlackJackGame发布卡，因为经销商与玩家完全相同。
// 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)
答案 0 :(得分：0)
你只向player3的deck[]添加了两张牌，所以当你拨打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......
而不是每个玩家都有一个名为deck的数组，而不是将其重命名为hand并使用ArrayList代替array，而ArrayList会允许你可以动态添加元素。
我会在您的switch方法中使用Card.Value()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);
}
您的改组算法几乎是正确的。
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.
}
它应该是这样的：
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;
}
我可以为getValue方法计算手数吗？
使用cCount所使用的数组，您可以使用一种方法来计算总手数：
public int calcHandTotal() {
int total = 0;
for(int i = 0; i < cCount; i++) {
total += deck[i].Value();
}
return total;
}