我正在制作黑色插卡游戏。我对我的程序错误感到困惑。任何帮助将受到高度赞赏。提前谢谢！
这是我运行代码时出现的错误：
线程“main”java.lang.NullPointerException中的异常 在BlackJackCardGame.DealHands（BlackJackCardGame.java:197） 在BlackJackCardGame.PlayBlackJack（BlackJackCardGame.java:207） 在BlackJackCardGame.main（BlackJackCardGame.java:252）
我的代码如下：
import java.util.Scanner;
//import java.util.*;
public class BlackJackCardGame
{
static class Player
{
private String Name;
private int handValue;
private boolean BlackJack;
private TheCard[] Hand;
public Player(String name)
{
this.Name = name;
this.handValue = 0;
this.BlackJack = false;
this.Hand = null;
}
}
private static Player[] InitializePlayers(int PlayerCount)
{
Player[] thePlayers = new Player[PlayerCount + 1];
for(int i = 0; i < PlayerCount + 1; i++)
{
String tempName;
if (i == 0)
{
tempName = "Dealer";
}
else
{
tempName = "Player_" + String.valueOf(i);
}
thePlayers[i] = new Player(tempName);
}
return thePlayers;
}
static class TheCard
{
// Java getter & setter
private String CardName;
private int CardRank;
private int Chosen;
public TheCard(int rank, String name)
{
this.CardName = name;
this.CardRank = rank;
this.Chosen = 0;
}
}
private static TheCard[] BuildDeck(int decks)
{
String[] Cards = {"2","3","4","5","6","7","8","9","10","Jack","Queen","King","Ace"};
String[] Suits = {"Spades","Hearts","Diamonds","Clubs"};
TheCard[] theDeck = new TheCard[Cards.length * Suits.length];
//int String [] = {2,3,4,5,6,7,8,9,10,11,12,13,14};
int[] Rank = {2,3,4,5,6,7,8,9,10,10,10,10,11};
int cardnumber = 0;
for (int d = 0; d < decks; d++)
{
for (int i = 0; i < Cards.length; i++)
{
for (int j = 0; j < Suits.length; j++)
{
String deckcard = Cards[i];
String suitcard = Suits[j];
String cardname = deckcard + "-" + suitcard;
theDeck[cardnumber] = new TheCard(Rank[i], cardname);
cardnumber++;
}
}
}
return theDeck;
}
private static TheCard Deal(TheCard[] OrderedDeck)
{ // this method uses Random method to "deal" a single card from the playing deck
TheCard thecard;
int NumberofCards = OrderedDeck.length;
int random = (int) (NumberofCards*Math.random ());
thecard = OrderedDeck[random];
if (thecard.Chosen == 0 ) // if available...
{
thecard.Chosen = 1; // mark it taken...
return thecard;
}
else
{
return Deal(OrderedDeck);
}
}
private static int ShowCardOfDealer(Player player, int cardNumber)
{
System.out.println (player.Name + ", is holding a: ");
System.out.println (player.Hand[cardNumber].CardName);
int value = player.Hand[cardNumber].CardRank;
System.out.println ("..with value of: " + String.valueOf(value));
return value;
}
private static void DealerPlays(TheCard[] deck,Player[] players)
{
Player currentPlayer = players[0]; // dealer first in array
int handValue = ShowHand(currentPlayer);
int choice = 1;
do
{
if (handValue < 17 )
{
TheCard newCard = Deal(deck);
int numCards = currentPlayer.Hand.length;
currentPlayer.Hand[numCards + 1] = newCard;
handValue = ShowHand(currentPlayer);
if (handValue > 21)
{
System.out.println ("The Dealer has busted!");
handValue = 0; // special signal that this value always loses
choice = 0;
}
}
else
{
System.out.println ("The Dealer stays.");
choice = 0; //dealer is forced to stay, =>17
}
} while ( choice == 1);
}
private static void MakeChoices(TheCard[] deck,Player[] players)
{
for( int i = 1; i < players.length -1 ; i++ )
{
Player currentPlayer = players[i];
int handValue = ShowHand(currentPlayer);
Scanner input = new Scanner(System.in);
int choice = 0;
do
{
System.out.println ("Make your choice please. Type 1 for Hit or type 0 for Stay.");
choice = input.nextInt();
if (choice == 1)
{
// DealAnotherCardToPlayerX
// what player is going to be updated
// add new card to players hand
TheCard newCard = Deal(deck);
int numCards = currentPlayer.Hand.length;
currentPlayer.Hand[numCards + 1] = newCard;
handValue = ShowHand(currentPlayer);
if (handValue > 21)
{
System.out.println ("You have busted!");
handValue = 0; // special signal that this value always loses
choice = 0; //this guy is done, loop to next player
}
}
} while ( choice == 1);
currentPlayer.handValue = handValue;
}
}
private static void setBlackJackCase(Player player)
{
player.BlackJack = false;
if (player.Hand[0].CardRank == 10 && player.Hand[1].CardRank == 11)
{
player.BlackJack = true;
}
if (player.Hand[1].CardRank == 10 && player.Hand[0].CardRank == 11)
{
player.BlackJack = true;
}
}
private static int ShowHand(Player player)
{
int cards = player.Hand.length; // get number of cards player x has
System.out.println (player.Name + ", you are holding: ");
int value = 0;
for (int c = 0; c < cards; c++ )
{
System.out.println (player.Hand[c].CardName);
//value = value + player.Hand[c].CardRank;
value += player.Hand[c].CardRank;
}
setBlackJackCase(player);
System.out.println ("Your total card value is: " + String.valueOf(value));
return value;
}
private static void DealHands(TheCard[] deck,Player[] players)
{
for (int c = 0; c < 2; c++)
{
for( int i = 1; i < players.length -1 ; i++ )
{
TheCard card = Deal(deck);
players[i].Hand[c] = new TheCard(card.CardRank, card.CardName);
}
//give dealer card
TheCard card = Deal(deck);
players[0].Hand[c] = new TheCard(card.CardRank, card.CardName);
}
}
private static void PlayBlackJack(TheCard[] playingDeck, Player[] players)
{
DealHands( playingDeck, players); // everybody has their hands - ready for choices:
ShowCardOfDealer ( players[0], 0); //shows dealer's turned up card
MakeChoices (playingDeck, players); // everybody is either out or at "stay"
DealerPlays (playingDeck, players); // Dealer "plays" and Dealer Rules
AnnounceWinners (players);
}
private static void AnnounceWinners(Player[] players)
{
int dealerHand = players[0].handValue;
for( int i = 1; i < players.length -1 ; i++ )
{
int playerHand = players[i].handValue;
if (players[i].BlackJack)
{
System.out.println (players[i].Name + ", you have BlackJack! :) You WIN!");
}
else
{
if (dealerHand == 0 && playerHand == 0)
{
System.out.println (players[i].Name + " has busted..");
}
if (dealerHand >= playerHand )
{
System.out.println ("Dealer wins" );
}
else
{
System.out.println (players[i].Name + ", you WIN!");
}
}
}
}
public static void main(String args[])
{
System.out.println ("Welcome, to the game of Black Jack");
Scanner input = new Scanner(System.in);
System.out.println ("How many decks of cards are in this game? Enter a number from 1 to 3.");
int decks = input.nextInt();
System.out.println ("How many players are in this game? (Not counting the Dealer)");
int numPlayers = input.nextInt();
TheCard[] PlayingDeck = BuildDeck(decks);
Player[] thePlayers = InitializePlayers(numPlayers);
//loop
PlayBlackJack(PlayingDeck, thePlayers);
System.out.println ("Play Again? Type 'y' or 'n'");
//test answer
}
}
答案 0 :(得分：2)
您没有提供足够的信息来轻松指出问题，但您可以获得所需的所有信息，因为您可以看到行号。找到第197行并查看该行上的每个对象。其中一个是null，你试图把它看作是一个有效的对象。
private static void DealHands(TheCard[] deck,Player[] players)
{
for (int c = 0; c < 2; c++)
{
for( int i = 1; i < players.length -1 ; i++ )
{
TheCard card = Deal(deck);
players[i].Hand[c] = new TheCard(card.CardRank, card.CardName);
}
//give dealer card
TheCard card = Deal(deck);
players[0].Hand[c] = new TheCard(card.CardRank, card.CardName);
}
}
我的猜测是你没有在Hand构造函数中初始化播放器的Player，因此players[i].Hand[c]会尝试访问null数组中的索引。首先需要将数组初始化为某个长度。
答案 1 :(得分：1)
请注意Player构造函数中的以下代码行：this.Hand = null; 。
答案 2 :(得分：1)
您没有正确初始化Player.Hand数组
你设置的Player类构造函数（第16行）中的
this.Hand = null;
在您的方法中
private static Player[] InitializePlayers(int PlayerCount)
在第19行，当你尝试执行以下操作时，不要更新它，所以在第196行（nullpointer）：
players[i].Hand[c] = new TheCard(card.CardRank, card.CardName);
玩家[i] .Hand []为空，所以你得到错误。确保在InitializePlayer方法中将Hand设置为非null数组。
（顺便说一句，普通的Java约定是方法和类成员名称的较低的驼峰情况，例如“Hand”等变量应该是“hand”，方法“InitializePlayer”应该像“initializePlayer”）
答案 3 :(得分：1)
public Player(String name) {
this.Name = name;
this.handValue = 0;
this.BlackJack = false;
this.Hand = null;
}
检查行this.Hand = null; 然后你用Hand at：
private static void DealHands(TheCard[] deck, Player[] players) {
for (int c = 0; c < 2; c++) {
for (int i = 1; i < players.length - 1; i++) {
TheCard card = Deal(deck);
players[i].Hand[c] = new TheCard(card.CardRank, card.CardName);
}
// give dealer card
TheCard card = Deal(deck);
System.out.print("Card == null" + card == null);
players[0].Hand[c] = new TheCard(card.CardRank, card.CardName);
}
}
这里在线： 玩家[0]。手[c] =新的TheCard（card.CardRank，card.CardName）;
所以试着宣布这个.Hand = new TheCard [2]; //这里2只是一个例子
然后，您的代码中还有另一个问题
private static void DealerPlays(TheCard[] deck, Player[] players) {
Player currentPlayer = players[0]; // dealer first in array
int handValue = ShowHand(currentPlayer);
int choice = 1;
do {
if (handValue < 17) {
TheCard newCard = Deal(deck);
int numCards = currentPlayer.Hand.length;
currentPlayer.Hand[numCards + 1] = newCard;
handValue = ShowHand(currentPlayer);
if (handValue > 21) {
System.out.println("The Dealer has busted!");
handValue = 0; // special signal that this value always
// loses
choice = 0;
}
} else {
System.out.println("The Dealer stays.");
choice = 0; // dealer is forced to stay, =>17
}
} while (choice == 1);
}
检查下面的行并修复它，这是类型“ArrayIndexOutOfBoundsException”的肯定例外。
int numCards = currentPlayer.Hand.length;
currentPlayer.Hand[numCards + 1] = newCard;
答案 4 :(得分：0)
堆栈顶部跟踪引用第197行。除非您的源代码段缺少行，否则第197行是：
players[i].Hand[c] = new TheCard(card.CardRank, card.CardName);
每次使用点运算符.访问对象时，如果被访问的对象为null，则会抛出NPE。尝试索引引用为null的数组变量时，也会抛出NPE。所以嫌疑人是：
players
players[i]
players[i].Hand
card
以上其中一项必须是null。我建议使用调试器在第197行中断并检查每个嫌疑人。一旦你发现哪一个是罪魁祸首，你就可以向后工作并试图弄清楚它是如何成为null的。{/ p>
（请注意，上面未包含card.CardRank和card.CardName;这是因为如果它们是问题，那么您的异常将从TheCard的构造函数中抛出。）