具有降序和升序的迭代器不工作

Question

我正在尝试实现以下实现Iterable的deque：

public class Dequeue<E> implements Iterable<E> {

    protected List<E> deque;

    public Dequeue() {
        this.deque = new ArrayList<>();

    }

    public void insertFirst( E elem ) {
        this.deque.add( 0, elem );
    }

    public void insertLast( E elem ) {
        this.deque.add( elem );
    }

    public E removeFirst() {
        return (this.deque.isEmpty()) ? null : this.deque.remove(0);
    }

    public E removeLast() {
        return (this.deque.isEmpty()) ? null : this.deque.remove( this.deque.size() - 1 );
    }

    public E examineFirst() {
        return this.deque.get(0);
    }

    public E examineLast() {
        return this.deque.get( this.deque.size() - 1 );
    }

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

    public Iterator<E> iterator( boolean isDesc ) {
        return new DequeIterator<>(isDesc);
    }

    public class DequeIterator<E> implements Iterator<E> {

        private int index;
        private boolean isDesc;

        public DequeIterator( boolean isdesc ) {
            this.index = isdesc ? deque.size() - 1 : 0;
        }

        @Override
        public boolean hasNext() {
            return isDesc ? index > 0 : index < deque.size();
        }

        @Override
        public E next() {
            this.index = (isDesc) ? index-- : index++;
            return (E) deque.get(index);
        }

        @Override
        public void remove() {
            deque.remove(index);
        }
    }

}

但是如果我试着用下面的代码测试它，它会进入一个无限循环。发生了什么事？编译器不会返回任何类型的错误，我也不知道迭代器类的实现是否正确。

List<Integer> result = new ArrayList<>();
Dequeue<Integer> deque = new Dequeue<>();
deque.insertLast( new Integer(1) );
deque.insertLast( new Integer(2) );

for( Integer i : deque ) {
    System.out.println(i);
}

Answer 1

实际上，你的代码中有3个错误：

1. 你不需要迭代deque，而是迭代无用的列表result

这里是代码固定：

Dequeue<Integer> deque = new Dequeue<>();
deque.insertLast(1);
deque.insertLast(2);

for( Integer i : deque ) {
    System.out.println(i);
}

和类DeQueue。dequeIterator

public class DequeIterator<E> implements Iterator<E> {

    ...
    private boolean isDesc;

    public DequeIterator( boolean isdesc ) {
        ...
        this.isDesc = isdesc;
    }

   ...

    @Override
    public E next() {
        return (E) deque.get(isDesc ? index-- : index++);
    }

    ...
}