为什么我的ArrayList抛出IndexOutOfBoundsException异常？

Question

我正在编写这种方法来创建一个洗牌的牌组:

public static ArrayList<String> shuffle() {
    String cards[] = {"Two of Spades","Three of Spades","Four of Spades","Five of Spades", "Six of Spades","Seven of Spades", "Eight of Spades", "Nine of Spades", "Ten of Spades", "Jack of Spades", "Queen of Spades", "King of Spades", "Ace of Spades", 
                      "Two of Hearts","Three of Hearts","Four of Hearts","Five of Hearts", "Six of Hearts","Seven of Hearts", "Eight of Hearts", "Nine of Hearts", "Ten of Hearts", "Jack of Hearts", "Queen of Hearts", "King of Hearts", "Ace of Hearts",
                      "Two of Clubs","Three of Clubs","Four of Clubs","Five of Clubs", "Six of Clubs","Seven of Clubs", "Eight of Clubs", "Nine of Clubs", "Ten of Clubs", "Jack of Clubs", "Queen of Clubs", "King of Clubs", "Ace of Clubs", 
                      "Two of Diamonds","Three of Diamonds","Four of Diamonds","Five of Diamonds", "Six of Diamonds","Seven of Diamonds", "Eight of Diamonds", "Nine of Diamonds", "Ten of Diamonds", "Jack of Diamonds", "Queen of Diamonds", "King of Diamonds", "Ace of Diamonds" };
    ArrayList<Integer> numbers = new ArrayList<Integer>();
    for (int i = 0; i < 52; i++) {
        numbers.add(i);
    }
    ArrayList<String> deck = new ArrayList<String>();
    for (int i = 0; i < 52; i++) {
        Random randomizer = new Random();
        int index = randomizer.nextInt(numbers.size());
        int number = numbers.get(index);
        deck.add(numbers.get(number), cards[i]);
        numbers.remove(index);
    }
    return deck;
}

我的问题是在deck.add上,我得到一个IndexOutOfBoundsException异常.我认为ArrayList会调整大小以适应.为什么会发生这种情况,我该如何解决？这是例外:

Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 23, Size: 0
    at java.util.ArrayList.rangeCheckForAdd(ArrayList.java:661)
    at java.util.ArrayList.add(ArrayList.java:473)
    at game.mainGame.shuffle(mainGame.java:182)
    at game.mainGame.main(mainGame.java:32)

Answer 1

异常有两个可能的原因.一个是你numbers在这两行中对索引进行双索引:

int number = numbers.get(index);
deck.add(numbers.get(number), cards[i]);

问题是,一旦你删除了一个数字numbers,那么其余数字之一很可能大于最大的合法指数.(实际上,除非您碰巧按严格降序生成索引,否则这是有保证的.)另一个原因在@default语言环境的答案中给出:您不能添加到任意位置deck; add()如果您尝试在大于列表当前长度的位置添加元素,则双参数调用将生成此异常.

我建议你只是Collections.shuffle(List)用来随机化numbers列表(或者更好的是,甲板本身),而不是实现你自己的shuffle .

这是我的版本shuffle():

private static final List<String> cards = Arrays.asList(
    "Two of Spades","Three of Spades","Four of Spades","Five of Spades", "Six of Spades","Seven of Spades", "Eight of Spades", "Nine of Spades", "Ten of Spades", "Jack of Spades", "Queen of Spades", "King of Spades", "Ace of Spades", 
    "Two of Hearts","Three of Hearts","Four of Hearts","Five of Hearts", "Six of Hearts","Seven of Hearts", "Eight of Hearts", "Nine of Hearts", "Ten of Hearts", "Jack of Hearts", "Queen of Hearts", "King of Hearts", "Ace of Hearts",
    "Two of Clubs","Three of Clubs","Four of Clubs","Five of Clubs", "Six of Clubs","Seven of Clubs", "Eight of Clubs", "Nine of Clubs", "Ten of Clubs", "Jack of Clubs", "Queen of Clubs", "King of Clubs", "Ace of Clubs", 
    "Two of Diamonds","Three of Diamonds","Four of Diamonds","Five of Diamonds", "Six of Diamonds","Seven of Diamonds", "Eight of Diamonds", "Nine of Diamonds", "Ten of Diamonds", "Jack of Diamonds", "Queen of Diamonds", "King of Diamonds", "Ace of Diamonds"
);

public static ArrayList<String> shuffle() {
    final ArrayList<String> deck = new ArrayList<String>(cards);
    Collections.shuffle(deck);
    return deck;
}