java - 为什么我收到错误“找不到方法”？

Question

我正在做一项需要使用队列的作业。部分代码直接来 self 的书，但是我在 ArrayUnbndQueue 类的出列方法中遇到了几个错误。

public class ArrayUnbndQueue<T> implements UnboundedQueueInterface<T>
{
    protected final int DEFCAP = 100; // default capacity
    protected T[] queue;              // array that holds queue elements
    protected int origCap;            // original capacity
    protected int numElements = 0;    // number of elements in the queue
    protected int front = 0;          // index of front of queue
    protected int rear = -1;          // index of rear of queue

    public ArrayUnbndQueue()
    {
        queue = (T[]) new Object [DEFCAP];
        rear = DEFCAP - 1;
        origCap = DEFCAP;
    }

    public ArrayUnbndQueue(int origCap)
    {
        queue = (T[]) new Object[origCap];
        rear = origCap - 1;
        this.origCap = origCap;
    }

    private void enlarge()
    {
        T[] larger = (T[]) new Object[queue.length + origCap];

        int currSmaller = front;
        for (int currLarger = 0; currLarger < numElements; currLarger++)
        {
            larger[currLarger] = queue[currSmaller];
            currSmaller = (currSmaller + 1) % queue.length;
        }

        // update instance variables
        queue = larger;
        front = 0;
        rear = numElements - 1;
    }

    public void enqueue(T element)
    {
        if (numElements == queue.length)
            enlarge();
        rear = (rear + 1) % queue.length;
        queue[rear] = element;
        numElements = numElements + 1;
    }

    public T dequeue()
    {
        if (isEmpty())
            throws new QueueUnderflowException("Dequeue attempted on empty queue.");
        else
            {
              T toReturn = queue[front];
              queue[front] = null;
              front = (front + 1) % queue.length;
              numElements = numElements -1;
              return toReturn;
            }
    }

    public boolean isEmpty()
    {
        return (numElements == 0);
    }

}

公共(public) T deque 方法完全是从我的书中复制的。QueueUnderflowException 类实际上并未在我的书中显示，因此我在接口(interface)和此类中遇到了其他错误，但我为此编写了代码

public class QueueUnderflowException extends RuntimeException
{
    public QueueUnderflowException()
    {
        super();
    }
    public QueueUnderflowException(String message)
    {
        super(message);
    }
}

Netbeans 给我一个错误，它无法找到方法 QueueUnderflowException，否则没有 if，并且缺少 return 语句。

我尝试在抛出异常行周围添加括号，如下面的代码。这消除了我的“else with no if”错误，并且我可能可以将 return 语句移至 else 语句的外部，但我仍然收到找不到方法错误

public T dequeue()
        {
            if (isEmpty())
            {
                throws new QueueUnderflowException("Dequeue attempted on empty queue.");
            }
            else
                {
                  T toReturn = queue[front];
                  queue[front] = null;
                  front = (front + 1) % queue.length;
                  numElements = numElements -1;
                  return toReturn;
                }
        }

Answer 1

抛出 new QueueUnderflowException("尝试在空队列上出队。");

应该是

抛出 new QueueUnderflowException("尝试在空队列上出列。");