package queues;

public interface Queue<E> extends Collection<E>{
	
	/*
	* Inserts the specified element into this queue if it is possible to do so immediately
	* without violating capacity restrictions, returning true upon success
	* and throwing an IllegalStateException if no space is currently available. 
	*/
	boolean add(E e);  //throws IllegalStateException, NullPointerException
	
	/*
	 * Inserts the specified element into this queue if it is possible to do so immediately
	 * without violating capacity restrictions. When using a capacity-restricted queue,
	 * this method is generally preferable to add(E), which can fail to insert an element
	 * only by throwing an exception. 
	 */
	boolean offer(E e);  //throws NullPointerException
	
	/*
	 * Retrieves and removes the head of this queue.
	 * This method differs from poll only in that it throws an exception
  *  if this queue is empty. 
	 */
	E remove(); //throws NoSuchElementException
	
	/*
	 * Retrieves and removes the head of this queue, or returns null if this queue is empty
	 */
	E poll(); 
	
	/*
	 * Retrieves, but does not remove, the head of this queue. 
	 * This method differs from peek only in that it throws an exception
 *  if this queue is empty. 
	 */
	E element();  //throws NoSuchElementException
	
	/*
	 * Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty. 
	 */
	E peek();  
}