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   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
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   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
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   *
   * You should have received a copy of the GNU General Public License version
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   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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  /*
   * This file is available under and governed by the GNU General Public
   * License version 2 only, as published by the Free Software Foundation.
   * However, the following notice accompanied the original version of this
   * file:
   *
   * Written by Doug Lea with assistance from members of JCP JSR-166
   * Expert Group and released to the public domain, as explained at
   * http://creativecommons.org/publicdomain/zero/1.0/
   */
  
  package java.util;
  
  // BEGIN android-note
  // removed link to collections framework docs
  // END android-note
  
  /**
   * A collection designed for holding elements prior to processing.
   * Besides basic {@link Collection Collection} operations,
   * queues provide additional insertion, extraction, and inspection
   * operations.  Each of these methods exists in two forms: one throws
   * an exception if the operation fails, the other returns a special
   * value (either {@code null} or {@code false}, depending on the
   * operation).  The latter form of the insert operation is designed
   * specifically for use with capacity-restricted {@code Queue}
   * implementations; in most implementations, insert operations cannot
   * fail.
   *
   * <table BORDER CELLPADDING=3 CELLSPACING=1>
   * <caption>Summary of Queue methods</caption>
   *  <tr>
   *    <td></td>
   *    <td ALIGN=CENTER><em>Throws exception</em></td>
   *    <td ALIGN=CENTER><em>Returns special value</em></td>
   *  </tr>
   *  <tr>
   *    <td><b>Insert</b></td>
   *    <td>{@link Queue#add add(e)}</td>
   *    <td>{@link Queue#offer offer(e)}</td>
   *  </tr>
   *  <tr>
   *    <td><b>Remove</b></td>
   *    <td>{@link Queue#remove remove()}</td>
   *    <td>{@link Queue#poll poll()}</td>
   *  </tr>
   *  <tr>
   *    <td><b>Examine</b></td>
   *    <td>{@link Queue#element element()}</td>
   *    <td>{@link Queue#peek peek()}</td>
   *  </tr>
   * </table>
   *
   * <p>Queues typically, but do not necessarily, order elements in a
   * FIFO (first-in-first-out) manner.  Among the exceptions are
   * priority queues, which order elements according to a supplied
   * comparator, or the elements' natural ordering, and LIFO queues (or
   * stacks) which order the elements LIFO (last-in-first-out).
   * Whatever the ordering used, the <em>head</em> of the queue is that
   * element which would be removed by a call to {@link #remove() } or
   * {@link #poll()}.  In a FIFO queue, all new elements are inserted at
   * the <em>tail</em> of the queue. Other kinds of queues may use
   * different placement rules.  Every {@code Queue} implementation
   * must specify its ordering properties.
   *
   * <p>The {@link #offer offer} method inserts an element if possible,
   * otherwise returning {@code false}.  This differs from the {@link
   * Collection#add Collection.add} method, which can fail to
   * add an element only by throwing an unchecked exception.  The
   * {@code offer} method is designed for use when failure is a normal,
   * rather than exceptional occurrence, for example, in fixed-capacity
   * (or &quot;bounded&quot;) queues.
   *
   * <p>The {@link #remove()} and {@link #poll()} methods remove and
   * return the head of the queue.
   * Exactly which element is removed from the queue is a
   * function of the queue's ordering policy, which differs from
   * implementation to implementation. The {@code remove()} and
   * {@code poll()} methods differ only in their behavior when the
   * queue is empty: the {@code remove()} method throws an exception,
   * while the {@code poll()} method returns {@code null}.
   *
   * <p>The {@link #element()} and {@link #peek()} methods return, but do
   * not remove, the head of the queue.
   *
   * <p>The {@code Queue} interface does not define the <i>blocking queue
   * methods</i>, which are common in concurrent programming.  These methods,
   * which wait for elements to appear or for space to become available, are
   * defined in the {@link java.util.concurrent.BlockingQueue} interface, which
   * extends this interface.
   *
   * <p>{@code Queue} implementations generally do not allow insertion
   * of {@code null} elements, although some implementations, such as
   * {@link LinkedList}, do not prohibit insertion of {@code null}.
   * Even in the implementations that permit it, {@code null} should
   * not be inserted into a {@code Queue}, as {@code null} is also
   * used as a special return value by the {@code poll} method to
   * indicate that the queue contains no elements.
   *
   * <p>{@code Queue} implementations generally do not define
   * element-based versions of methods {@code equals} and
   * {@code hashCode} but instead inherit the identity based versions
   * from class {@code Object}, because element-based equality is not
   * always well-defined for queues with the same elements but different
   * ordering properties.
   *
   * @since 1.5
   * @author Doug Lea
   * @param <E> the type of elements held in this queue
   */
  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
       * {@code true} upon success and throwing an {@code IllegalStateException}
       * if no space is currently available.
       *
       * @param e the element to add
       * @return {@code true} (as specified by {@link Collection#add})
       * @throws IllegalStateException if the element cannot be added at this
       *         time due to capacity restrictions
       * @throws ClassCastException if the class of the specified element
       *         prevents it from being added to this queue
       * @throws NullPointerException if the specified element is null and
       *         this queue does not permit null elements
       * @throws IllegalArgumentException if some property of this element
       *         prevents it from being added to this queue
       */
      boolean add(E e);
  
      /**
       * 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 {@link #add}, which can fail to insert an element only
       * by throwing an exception.
       *
       * @param e the element to add
       * @return {@code true} if the element was added to this queue, else
       *         {@code false}
       * @throws ClassCastException if the class of the specified element
       *         prevents it from being added to this queue
       * @throws NullPointerException if the specified element is null and
       *         this queue does not permit null elements
       * @throws IllegalArgumentException if some property of this element
       *         prevents it from being added to this queue
       */
      boolean offer(E e);
  
      /**
       * Retrieves and removes the head of this queue.  This method differs
       * from {@link #poll poll} only in that it throws an exception if this
       * queue is empty.
       *
       * @return the head of this queue
       * @throws NoSuchElementException if this queue is empty
       */
      E remove();
  
      /**
       * Retrieves and removes the head of this queue,
       * or returns {@code null} if this queue is empty.
       *
       * @return the head of this queue, or {@code null} if this queue is empty
       */
      E poll();
  
      /**
       * Retrieves, but does not remove, the head of this queue.  This method
       * differs from {@link #peek peek} only in that it throws an exception
       * if this queue is empty.
       *
       * @return the head of this queue
       * @throws NoSuchElementException if this queue is empty
       */
      E element();
  
      /**
       * Retrieves, but does not remove, the head of this queue,
       * or returns {@code null} if this queue is empty.
       *
       * @return the head of this queue, or {@code null} if this queue is empty
       */
      E peek();
  }
  