如何在Java中实现嵌套的迭代器类

Question

I have a class, Deck , which holds an ArrayList of type <Card> . I'm trying to implement a couple of nested Iterator classes inside Deck (without the use of ListIterator - the first being one that simply traverses through the ArrayList<Card> held by Deck , in order. However, I'm having trouble getting it to work properly:

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;
        }
    }
}

Here's my main :

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

I'm getting 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

As the error says : in the DeckIterator class there is only one constructor, and it requires a List<Card> but you try to create a DeckIterator without any parameter

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

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

---

The default constructor (no arg) is available by default when there is no constructor define, it there is one, you need to explicitly define the default one (or give a List<Card> as parameter, because here you can't expect nothin in your loop as you didn't give any card)

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

---

Error : You did not use the variable name, it should be

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