java - 添加到ArrayList时出现NullPointer

Question

我意识到已经有一堆这样的问题，但到目前为止我看到的每个问题都是 ArrayList 未初始化。我认为我的已初始化，但在尝试添加到列表时我得到一个空指针。这是我的代码:

import java.util.ArrayList;
import java.util.Random;
import java.util.Collections;

public class Deck {
    static final int DECKSIZE = 48;
    static final int MAX = 10;
    static final int MIN = 1;
    public ArrayList<Card> cardDeck = new ArrayList<Card>();
    Random rand;

    public Deck() {
        initializeDeck();
    }

    private void initializeDeck() {
        for (int i=0; i<DECKSIZE; i++) {
            cardDeck.add(i, new Card("Name" + (i+1),  "Race" + (i+1), "Orientation" + (i+1)));
        }
    }

    public void shuffleCards() {
        Collections.shuffle(cardDeck);
    }
}

这是堆栈跟踪告诉我initializeDeck是一个空指针

Caused by: java.lang.NullPointerException
    at hr.krypto.cardwars.deck.Deck.initializeDeck(Deck.java:24)
    at hr.krypto.cardwars.deck.Deck.<init>(Deck.java:15)
    at hr.krypto.cardwars.deck.Dealer.<init>(Dealer.java:14)
    at hr.krypto.cardwars.model.CardTable.<init>(CardTable.java:15)
    at hr.krypto.cardwars.screen.GameScreen.show(GameScreen.java:31)
    at com.badlogic.gdx.Game.setScreen(Game.java:62)
    at hr.krypto.cardwars.CardWarsGame.create(CardWarsGame.java:19)
    at com.badlogic.gdx.backends.lwjgl.LwjglApplication.mainLoop(LwjglApplication.java:127)
    at com.badlogic.gdx.backends.lwjgl.LwjglApplication$1.run(LwjglApplication.java:110)

Answer 1

考虑到方法 ArrayList.add(index, Element) 仅抛出 IndexOutOfBoundsException，该错误必定出现在您的卡类的构造函数中。

猜测最快的方法是调试卡类构造函数。