在我进行测试时，我发现了我的代码中的错误。
我很难找到我的Deque迭代器出了什么问题。它没有正确迭代，我不知道如何修复它。我已经包含了失败测试的屏幕截图和我完成的代码。
附注：我的教授希望迭代器在向前迭代或反向迭代时从头部出列元素，这就是为什么迭代器更难弄清楚的原因。
失败的单元测试截图： https ://imgur.com/a/srlmrNQ
非常感谢你的帮助！
完整的源代码：
import java.util.Iterator;
import java.util.NoSuchElementException;
public class Deque<E> implements Iterable<E>
{
private class DequeNode<E>
{
private DequeNode<E> _next;
private DequeNode<E> _previous;
private E _data;
private DequeNode(E data)
{
_data = data;
}
}
private DequeNode<E> _head;
private DequeNode<E> _tail;
private int _depth;
private static final int EXCLUSIVE_INDEX_START = -1;
public Deque()
{
_head = null;
_tail = null;
_depth = 0;
}
public boolean enqueue(E element) // This is INSERTION at the TAIL //TODO: DONE!!
{
DequeNode<E> newNode = new DequeNode<E>(element);
if (isEmpty())
{
_head = newNode;
}
else
{
_tail._next = newNode;
newNode._previous = _tail;
}
_tail = newNode;
_depth++;
return true;
}
public void enqueueAll(Iterable<E> elements)
{
for (E eachElement : elements)
{
enqueue(eachElement);
}
}
public boolean enqueueHead(E element) // This is insertion at the head //TODO: DONE!!
{
DequeNode<E> newNode = new DequeNode<E>(element);
if (isEmpty())
{
_tail = newNode;
}
else
{
_head._previous = newNode;
newNode._next = _head;
}
_head = newNode;
_depth++;
return true;
}
public E head()
{
checkForStackUnderflow();
return _head._data;
}
public E tail()
{
checkForStackUnderflow();
return _tail._data;
}
public E dequeue() // This is removal at the head //TODO: DONE!!
{
checkForStackUnderflow();
E removed = _head._data;
if (_head._next == null)
{
_tail = null;
}
else
{
_head._next._previous = null;
}
_head = _head._next;
_depth--;
return removed;
}
public E dequeueTail() // This is removal at the tail //TODO: DONE!!
{
checkForStackUnderflow();
E removed = _tail._data;
if (_head._next == null)
{
_head = null;
}
else
{
_tail._previous._next = null;
}
_tail = _tail._previous;
_depth--;
return removed;
}
public void clear()
{
_head = _tail = null;
_depth = 0;
}
public int depth()
{
return _depth;
}
public boolean isEmpty()
{
return _depth == 0;
}
public Iterator<E> iterator()
{
return new DequeIterator(this, false);
}
public Iterator<E> reverseIterator()
{
return new DequeIterator(this, true);
}
private void checkForStackUnderflow()
{
if (isEmpty())
{
throw new NoSuchElementException("Stack underflow captain!!!");
}
}
private class DequeIterator implements Iterator<E>
{
// The instance variables used throughout the program.
private int _index;
private Deque<E> _theList;
private DequeNode<E> _current;
private boolean _iterateReverse;
public DequeIterator(Deque<E> deque, boolean reverse)
{
_theList = deque;
_iterateReverse = reverse;
_index = 0;
_current = _head;
/* If the flag for reverse iteration is detected, then just start
the index at the end and iterate from the tail.
*/
if (reverse)
{
_index = _theList._depth - 1;
_current = _theList._tail;
}
}
public boolean hasNext()
{
boolean results;
// If we are reverse iterating check if the index is > than -1.
if (_iterateReverse)
{
results = _index > EXCLUSIVE_INDEX_START;
}
/* Getting here means that we are forward iterating so check if the
index is less than size AKA if we have more elements to go through.
*/
else
{
results = _index < _theList._depth;
}
return results;
}
public E next()
{
// If we don't have more elements to iterate through then we throw.
if (!hasNext())
{
throw new NoSuchElementException();
}
// Update the current to descent if we are reverse iterating.
if (_iterateReverse)
{
_current = _current._previous;
_index--;
}
// If we get to here then just update the current value forward.
else
{
_current = _current._next;
_index++;
}
return dequeue();
}
}
}