如何在Java中實現嵌套的迭代器類

Question

我有一個Deck類，其中包含一個<Card>類型的ArrayList 。 我正在嘗試在Deck實現幾個嵌套的Iterator類（不使用ListIterator －第一個是簡單地按順序遍歷Deck持有的ArrayList<Card> 。但是，我很難獲取它正常工作：

private static class DeckIterator implements Iterator<Card> {
    private int nextCard;
    private final ArrayList<Card> cards;

    public DeckIterator(ArrayList<Card> cards) {
        this.cards = cards;
        this.nextCard = 0;
    }

    @Override
    public boolean hasNext() {
        if (nextCard > cards.size() - 1) {
            return false;
        }
        else {
            return true;
        }
    }

    @Override
    public Card next() {
        if (hasNext() == true) {
            return cards.get(nextCard + 1);
        }
        else {
            return null;
        }
    }
}

這是我的main ：

public static void main(String[] args) {
        Deck newDeck = new Deck();
        Iterator<Card> iterator = new DeckIterator();
        while (DeckIterator.hasNext()) {
            Card card = DeckIterator.next();
        }
    }
}

我constructor DeckIterator in class DeckIterator cannot be applied to given types; required: ArrayList<Card>, found: no arguments得到constructor DeckIterator in class DeckIterator cannot be applied to given types; required: ArrayList<Card>, found: no arguments constructor DeckIterator in class DeckIterator cannot be applied to given types; required: ArrayList<Card>, found: no arguments 。

Answer 1

如錯誤所示：在DeckIterator類中只有一個構造函數，它需要一個List<Card>但是您嘗試創建一個不帶任何參數的DeckIterator

// REQUIRE
public DeckIterator(ArrayList<Card> cards) {
    this.cards = cards;
    this.nextCard = 0;
}

// YOUR TRY
Iterator<Card> iterator = new DeckIterator();

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當沒有構造函數定義時，默認情況下默認構造函數（no arg）可用，它有一個，您需要顯式定義默認構造函數（或給List<Card>作為參數，因為在這里您不能指望沒什么因為您沒有給任何卡片而在循環中）

public DeckIterator() {
    this.cards = new ArrayList<>();
    this.nextCard = 0;
}

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錯誤 ：您未使用變量名，應該是

while (iterator.hasNext()) {
    Card card = iterator .next();
}