package username.linear;

/**
 * A linear structure that follows the "first in, first out" policy.
 *
 * @author Samuel A. Rebelsky
 * @version 1.0 of March 2005
 */
public interface Queue<T>
  extends LinearStructure<T>
{
  /**
   * Add an element to the end of the queue.
   *
   * @param val
   *   The object that is to be added.
   * @post
   *   The queue now contains an additional copy of val.
   */
  public void put(T val);

  /**
   * Remove the least-recently-added element that is still in the
   * queue.
   *
   * @return val
   *   A value in the queue.
   * @pre
   *   The queue is not empty.
   * @post
   *   The queue contains one fewer copy of val.
   * @post
   *   Every value in the queue was added more recently than val.
   */
  public T get();

  /**
   * Determine which object will next be returned by get.
   *
   * @return val
   *   An object in the queue.
   * @pre
   *   The queue is not empty.
   * @post
   *   Every value in the queue was added less recently than val.
   */
  public T peek();

  /**
   * Determine if the queue is empty.
   */
  public boolean isEmpty();

} // interface Queue<T>