//---------------------------------------------------------------------------
// ArrayBndQueue.java          by Dale/Joyce/Weems                  Chapter 5
//
// Implements BoundedQueueInterface with an array to hold the queue elements.
//
// Two constructors are provided: one that creates a queue of a default
// capacity and one that allows the calling program to specify the capacity.
//---------------------------------------------------------------------------

package ch05.queues;

public class ArrayBndQueue<T> implements BoundedQueueInterface<T>
{
  protected final int DEFCAP = 100; // default capacity
  protected T[] queue;              // array that holds queue elements
  protected int numElements = 0;    // number of elements n the queue
  protected int front = 0;          // index of front of queue
  protected int rear;               // index of rear of queue

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

  public ArrayBndQueue(int maxSize) 
  {
    queue = (T[]) new Object[maxSize];
	 rear = maxSize - 1;
  }

  public void enqueue(T element)
  // Throws QueueOverflowException if this queue is full;
  // otherwise, adds element to the rear of this queue.
  {  
    if (isFull())
      throw new QueueOverflowException("Enqueue attempted on a full queue.");
    else
    {
      rear = (rear + 1) % queue.length;
      queue[rear] = element;
      numElements = numElements + 1;
    }
  }

  public T dequeue()
  // Throws QueueUnderflowException if this queue is empty;
  // otherwise, removes front element from this queue and returns it.
  {   
    if (isEmpty())
      throw 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()
  // Returns true if this queue is empty; otherwise, returns false
  {              
    return (numElements == 0);
  }

  public boolean isFull()
  // Returns true if this queue is full; otherwise, returns false.
  {              
    return (numElements == queue.length);
  }
}