使用Java中的圆形链接队列创建出队方法

Question

我在弄清楚如何完成我的出队方法时遇到了麻烦。 我只允许使用后指针实例变量。 我从队列中删除了前两个条目，但随后它没有删除其余的条目。 我的代码如下。 我非常困惑我的方法正在发生什么。 谢谢

public class CircularLinkedQueue<T> implements QueueInterface<T>
{
private Node lastNode;

@Override
public void enqueue(Object newEntry) 
{
    Node newNode = new Node(newEntry, null);
    if(lastNode == null)
        newNode.setNextNode(newNode);
    else
    {
        newNode.setNextNode(lastNode.getNextNode());
        lastNode.setNextNode(newNode);
    }
    lastNode = newNode;
}

@SuppressWarnings("unchecked")
@Override
public T dequeue() 
{
    T result = null;
    if(!isEmpty())
    {
        result = (T) lastNode.getNextNode().getData();
        lastNode = lastNode.getNextNode();

        if(lastNode.getNextNode() == null)
            lastNode = null;
        else
            lastNode.getNextNode().setNextNode(null);
    }
    return  result;
}

@Override
public T getFront() 
{
    T results = null;
    if(!isEmpty())
        results = (T) lastNode.getNextNode().getData();
    return results;
}

@Override
public boolean isEmpty() 
{
    if(lastNode == null)
        return true;
    else return false;
}

@Override
public void clear() 
{
    lastNode = null;
}

}

我的出队驱动程序应该是这样的。

    public static void main(String[] args) {

    System.out.println("Create a queue: ");
    QueueInterface<String> myQueue = new CircularLinkedQueue<String>();
    myQueue.enqueue("Ann");
    myQueue.enqueue("Bill");
    myQueue.enqueue("Carol");
    myQueue.enqueue("David");
    myQueue.enqueue("Edgar");
    myQueue.enqueue("Fred");

    while (!myQueue.isEmpty()) {
        Object front = myQueue.getFront();
        System.out.println("\t" + front + " is at the front of the queue.");

        front = myQueue.dequeue();
        System.out.println("\t" + front + " is removed from the front of the queue.");
    } 
}  
}

输出应如下所示

Ann is at the front of the queue.

Ann is removed from the front of the queue.

Bill is at the front of the queue.

Bill is removed from the front of the queue.

Carol is at the front of the queue.

Carol is removed from the front of the queue.

David is at the front of the queue.

David is removed from the front of the queue.

Edgar is at the front of the queue.

Edgar is removed from the front of the queue.
Fred is at the front of the queue.

Fred is removed from the front of the queue.

我的输出看起来像这样

Ann is removed from the front of the queue.

Bill is at the front of the queue.

Bill is removed from the front of the queue.

Answer 1

您的出队方法有问题。 （我认为）这应该是：

public T dequeue() {
    if (isEmpty()) {
        throw new NoSuchElementException("The queue is empty!");
    }

    T result = lastNode.getNextNode().getData();

    if (lastNode.getNextNode() == lastNode) {
        lastNode = null;
    } else {
        lastNode.setNextNode(lastNode.getNextNode().getNextNode()); 
    }
    return result;
}