java - 二十一点Java : Exception Error

Question

我的 BlackJack Java 游戏出现错误。错误是:

Exception in thread "main" java.lang.NullPointerException<br/> at com.keegan.game.blackjack.Deck.createDeck(Deck.java:48)<br/> at com.keegan.game.blackjack.Deck.<init>(Deck.java:33)

而且我对这段代码中的问题一无所知。任何人都可以帮助我理解错误告诉我的是什么错误吗？

这是 Deck.java 的代码:

public class Deck {

private ArrayList<Card> deck = new ArrayList<Card>();

private List<Card> cardUsed = new ArrayList<Card>();
Card c = new Card(null, null, null, 0);

public Deck(int numCards) {
    this.createDeck(numCards, 4, null);
}

private void createDeck(int numCards, int numSuits, String[] cardRanks) {
    deck = new ArrayList<Card>();
    cardUsed = new ArrayList<Card>();
    if ((numCards % numSuits) > 0) return;
    for (int i=0; i < numSuits; i++) {
        for(int j=1; j <= (numCards / numSuits); j++) {
            deck.add(new Card(new Suit(i), cardRanks[j-1], cardRanks, j));
        }
    }
}

public Card dealCard( ) {

    Card dealtCard = null;
    if (deck.size() == 0){
        deck.addAll(cardUsed);
        this.shuffle();
        cardUsed = new ArrayList<Card>();
    }

    dealtCard = deck.get(0);
    deck.remove(0);
    cardUsed.add(dealtCard);

    return dealtCard;
}

public void shuffle() {
    Collections.shuffle(deck);
}

public ArrayList<Card> getDeck() {
    return deck;
}

public void setDeck(ArrayList<Card> deck) {
    this.deck = deck;
}
public int getNumUsedCards() {
    return cardUsed.size();
}

public List<Card> getCardUsed() {
    return cardUsed;
}

public void setCardUsed(List<Card> cardUsed) {
    this.cardUsed = cardUsed;
}

Answer 1

你正在传递一个null数组

this.createDeck(numCards, 4, null);

然后在您的语句中将其作为 cardRanks[j-1] 访问

deck.add(new Card(new Suit(i), cardRanks[j-1], cardRanks, j));

编辑:
您可能需要将 Deck 创建为

this.createDeck(numCards, 4);

并将Card添加为

deck.add(new Card(new Suit(i), j));

因为 String[] cardRanks 已经在您的 Card 类中初始化。而且，在设计方面它是正确的，因为 Deck 不应该知道卡片等级。 Card 应该将其封装起来，也许还实现 Comparable。