在 Java 中使用 LinkedList 创建一副扑克牌

Question

我不确定我在这里做什么，但我正在尝试使用 Java 中的 LinkedList 集合来创建一副扑克牌。我的逻辑似乎有错误。我在甲板构造函数中不断收到 NullPointerException。

我正在尝试修改使用数组来使用 LikedList 的代码。我错过了什么？

public class Deck {

/** 
 * A LinkedList of cards in the deck, where the top card is the 
 * first index.
 */
private LinkedList<Card> mCards;

/**
 * Number of cards currently in the deck
 */
private int numCards;


/**No args Constructor- if no arguments are used when creating a deck,
 * then we define the game deck to be one deck without shuffling.
 * 
 */
public Deck(){ this(1, false); }

/**Constructor that defines the number of decks (how many sets of 52
 *              cards are in the deck) and whether it should be shuffled.
 * 
 * @param numDecks the number of individual decks in this game deck
 * @param isShuffled whether to shuffle the cards
 */
public Deck(int numDecks, boolean isShuffled){

    this.numCards = numDecks * 52;

    //for each deck
    for (int i = 0; i < numDecks; i++){

        //for each suit
        for(int j = 0; j < 4; j++){

            //for each number
            for(int k = 1; k <= 13; k++){

                //add card to the deck
                this.mCards.add(new Card(Suit.values()[j], k));
            }
        }
    }
    if(isShuffled){
        this.shuffle();
}

---

public enum Suit {
   Clubs,
   Diamonds,
   Spades,
   Hearts,
}

Answer 1

你永远不会初始化mCards。

添加（在构造函数的开头）：

mCards = new LinkedList<Card>();