// Introduced in Chapter 4/** A first-in, first-out queue of Objects. */public interface Queue<E> {  /** Add target to the back of this Queue. */  public void add(E target);  /** Return true if this Queue is empty. */  public boolean isEmpty();  /**   * Remove and return the front item from this Queue.   * @throws EmptyStructureException if the Queue is empty.   */  public E remove();}