/**
 * Interface to define an abstract Quack (Stack + Queue)
 * @author Jay Summet - Georgia Tech
 */
public interface Quack<E> {

   /**
   * Add an element onto the tail of the Quack
   * Throws a RuntimeException if the underlying storage mechanism is out of room
   * @param element the element to add to the end of the Quack
   */
  public void enqueue(E element) throws java.lang.RuntimeException;
  
  /**
   * Push an element onto the top (head) of the Quack
   * Throws a RuntimeException if the underlying storage mechanism is out of room
   * @param element the element to add to the top of the Quack
   */
  public void push(E element) throws java.lang.RuntimeException;

  /**
   * Peek at, but don't remove, the head of the Quack
   * @return the head of the Quack (top) - Returns null if the Quack is empty
   */
  public E peek();

  /**
   * Pop an object from the Quack
   *  
   * @return the head (top) of the Quack and
   * remove it from the Quack - Returns null if the Quack is empty
   */
  public E pop();

  /**
   * Dequeue an object from the Quack (Note: Same behavior as Pop!)
   *  
   * @return the head (top) of the Quack and
   * remove it from the Quack - Returns null if the Quack is empty
   */
  public E dequeue();
  
  /**
   * Return the size of the Quack
   * @return the number of elements in the Quack
   */
  public int size();

  /**
   * Method to see if the Quack is empty
   * @return true if the Quack is empty, else false
   */
  public boolean isEmpty();
}