Question

在Iterator中实现的方法“next”中有一个错误。我不能返回'e'值，因为Java说它是Object类型。我不明白为什么。因为在Elem类中，如果我给出Point对象，它必须返回它。但我不太了解泛型，也许有人可以解释plz。日Thnx）

package Tutorial3;

import java.util.Iterator;


public class MyLinkedList<E> implements Iterable<E> {
    Elem<E> head;
    Elem<E> tail;

    public MyLinkedList() {
        head = null;
        tail = null;
    }

    public void add(E e) {
        Elem<E> newElem = new Elem<E>(e);
        if (head == null) {
            tail.setNext(newElem);
            head = newElem;
            tail = newElem;
        } else {
            tail.setNext(newElem);
            tail = newElem;
        }
    }

    public void addToHead(E e) {
        Elem<E> newElem = new Elem<E>(e);
        newElem.setNext(head);
        head = newElem;
    }

    public void addToTail(E e) {
        add(e);
    }

    public void removeFirstValue() {
        head = head.getNext();
    }

    public void removeLastValue() {
        Elem<E> cursor;
        cursor = head;
        while (cursor.getNext() != tail) {
            cursor = cursor.getNext();
        }
        tail = cursor;
        tail.setNext(null);
    }

    public E get(int index) {
        if ((index + 1) > size()) {
            throw new IndexOutOfBoundsException("Index: " + index + " Size: " + size());
        } else {
            Elem<E> cursor;
            cursor = head;
            int i = 0;
            if (i == index) {
                return cursor.getE();
            } else {
                while (i != index) {
                    cursor = cursor.getNext();
                    i++;
                }
                return cursor.getE();
            }
        }
    }

    public int size() {
        Elem<E> cursor;
        cursor = head;
        int size = 0;
        while (cursor != null) {
            size++;
            cursor = cursor.getNext();
        }
        return size;
    }

    @Override
    public Iterator<E> iterator() {
        return new MyLinkedListIterator<E>();
    }

    private class MyLinkedListIterator<T> implements Iterator<T> {
        private Elem elem = head;

        @Override
        public boolean hasNext() {
            return elem.getNext() != null;
        }

        @Override
        public T next() {
            return elem.getNext().getE();  //here is mistake: can't return e
                                           //required : T, Found: Object
        }
    }
}

package Tutorial3;

public class Elem<E> {
    private E e;
    private Elem<E> next;

    public Elem(E e) {
        this.e = e;
    }

    public Elem(E e, Elem<E> next) {
        this.e = e;
        this.next = next;
    }

    public E getE() {
        return e;
    }

    public void setE(E e) {
        this.e = e;
    }

    public Elem<E> getNext() {
        return next;
    }

    public void setNext(Elem<E> next) {
        this.next = next;
    }
}

Answer 1

应该是

private class MyLinkedListIterator implements Iterator<E> {
    private Elem<E> elem = head;

    @Override
    public boolean hasNext() {
        return elem.getNext() != null;
    }

    @Override
    public E next() {
        return elem.getNext().getE();
    }
}

您的MyLinkedListIterator类型应该从外部E类型继承MyLinkedList<E>，而不是声明自己的元素类型T，然后通过使用raw {来复合它{1}}输入而不是Elem。

我如何在迭代器<e>的“下一步”方法中返回？

1 个答案: