content: /*
   * 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
   * by Oracle in the LICENSE file that accompanied this code.
   *
   * 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
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   * or visit www.oracle.com if you need additional information or have any
   * questions.
   */
  
  /*
   * 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
  
  /**
   * This class provides skeletal implementations of some {@link Queue}
   * operations. The implementations in this class are appropriate when
   * the base implementation does <em>not</em> allow {@code null}
   * elements.  Methods {@link #add add}, {@link #remove remove}, and
   * {@link #element element} are based on {@link #offer offer}, {@link
   * #poll poll}, and {@link #peek peek}, respectively, but throw
   * exceptions instead of indicating failure via {@code false} or
   * {@code null} returns.
   *
   * <p>A {@code Queue} implementation that extends this class must
   * minimally define a method {@link Queue#offer} which does not permit
   * insertion of {@code null} elements, along with methods {@link
   * Queue#peek}, {@link Queue#poll}, {@link Collection#size}, and
   * {@link Collection#iterator}.  Typically, additional methods will be
   * overridden as well.  If these requirements cannot be met, consider
   * instead subclassing {@link AbstractCollection}.
   *
   * @since 1.5
   * @author Doug Lea
   * @param <E> the type of elements held in this queue
   */
  public abstract class AbstractQueue<E>
      extends AbstractCollection<E>
      implements Queue<E> {
  
      /**
       * Constructor for use by subclasses.
       */
      protected AbstractQueue() {
      }
  
      /**
       * 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.
       *
       * <p>This implementation returns {@code true} if {@code offer} succeeds,
       * else throws an {@code IllegalStateException}.
       *
       * @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
       */
      public boolean add(E e) {
          if (offer(e))
              return true;
          else
              throw new IllegalStateException("Queue full");
      }
  
      /**
       * 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.
       *
       * <p>This implementation returns the result of {@code poll}
       * unless the queue is empty.
       *
       * @return the head of this queue
       * @throws NoSuchElementException if this queue is empty
       */
      public E remove() {
          E x = poll();
          if (x != null)
              return x;
          else
              throw new NoSuchElementException();
      }
  
      /**
       * 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.
       *
       * <p>This implementation returns the result of {@code peek}
       * unless the queue is empty.
       *
       * @return the head of this queue
       * @throws NoSuchElementException if this queue is empty
       */
      public E element() {
          E x = peek();
          if (x != null)
              return x;
          else
              throw new NoSuchElementException();
      }
  
      /**
       * Removes all of the elements from this queue.
       * The queue will be empty after this call returns.
       *
       * <p>This implementation repeatedly invokes {@link #poll poll} until it
       * returns {@code null}.
       */
      public void clear() {
          while (poll() != null)
              ;
      }
  
      /**
       * Adds all of the elements in the specified collection to this
       * queue.  Attempts to addAll of a queue to itself result in
       * {@code IllegalArgumentException}. Further, the behavior of
       * this operation is undefined if the specified collection is
       * modified while the operation is in progress.
       *
       * <p>This implementation iterates over the specified collection,
       * and adds each element returned by the iterator to this
       * queue, in turn.  A runtime exception encountered while
       * trying to add an element (including, in particular, a
       * {@code null} element) may result in only some of the elements
       * having been successfully added when the associated exception is
       * thrown.
       *
       * @param c collection containing elements to be added to this queue
       * @return {@code true} if this queue changed as a result of the call
       * @throws ClassCastException if the class of an element of the specified
       *         collection prevents it from being added to this queue
       * @throws NullPointerException if the specified collection contains a
       *         null element and this queue does not permit null elements,
       *         or if the specified collection is null
       * @throws IllegalArgumentException if some property of an element of the
       *         specified collection prevents it from being added to this
       *         queue, or if the specified collection is this queue
       * @throws IllegalStateException if not all the elements can be added at
       *         this time due to insertion restrictions
       * @see #add(Object)
       */
      public boolean addAll(Collection<? extends E> c) {
          if (c == null)
              throw new NullPointerException();
          if (c == this)
              throw new IllegalArgumentException();
          boolean modified = false;
          for (E e : c)
              if (add(e))
                  modified = true;
          return modified;
      }
  
  }
  