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| 1 | +/* | |
| 2 | + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | |
| 3 | + * | |
| 4 | + * This code is free software; you can redistribute it and/or modify it | |
| 5 | + * under the terms of the GNU General Public License version 2 only, as | |
| 6 | + * published by the Free Software Foundation. Oracle designates this | |
| 7 | + * particular file as subject to the "Classpath" exception as provided | |
| 8 | + * by Oracle in the LICENSE file that accompanied this code. | |
| 9 | + * | |
| 10 | + * This code is distributed in the hope that it will be useful, but WITHOUT | |
| 11 | + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
| 12 | + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
| 13 | + * version 2 for more details (a copy is included in the LICENSE file that | |
| 14 | + * accompanied this code). | |
| 15 | + * | |
| 16 | + * You should have received a copy of the GNU General Public License version | |
| 17 | + * 2 along with this work; if not, write to the Free Software Foundation, | |
| 18 | + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | |
| 19 | + * | |
| 20 | + * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | |
| 21 | + * or visit www.oracle.com if you need additional information or have any | |
| 22 | + * questions. | |
| 23 | + */ | |
| 24 | + | |
| 25 | +/* | |
| 26 | + * This file is available under and governed by the GNU General Public | |
| 27 | + * License version 2 only, as published by the Free Software Foundation. | |
| 28 | + * However, the following notice accompanied the original version of this | |
| 29 | + * file: | |
| 30 | + * | |
| 31 | + * Written by Doug Lea with assistance from members of JCP JSR-166 | |
| 32 | + * Expert Group and released to the public domain, as explained at | |
| 33 | + * http://creativecommons.org/publicdomain/zero/1.0/ | |
| 34 | + */ | |
| 35 | + | |
| 36 | +package java.util; | |
| 37 | + | |
| 38 | +/** | |
| 39 | + * This class provides skeletal implementations of some {@link Queue} | |
| 40 | + * operations. The implementations in this class are appropriate when | |
| 41 | + * the base implementation does <em>not</em> allow <tt>null</tt> | |
| 42 | + * elements. Methods {@link #add add}, {@link #remove remove}, and | |
| 43 | + * {@link #element element} are based on {@link #offer offer}, {@link | |
| 44 | + * #poll poll}, and {@link #peek peek}, respectively, but throw | |
| 45 | + * exceptions instead of indicating failure via <tt>false</tt> or | |
| 46 | + * <tt>null</tt> returns. | |
| 47 | + * | |
| 48 | + * <p>A <tt>Queue</tt> implementation that extends this class must | |
| 49 | + * minimally define a method {@link Queue#offer} which does not permit | |
| 50 | + * insertion of <tt>null</tt> elements, along with methods {@link | |
| 51 | + * Queue#peek}, {@link Queue#poll}, {@link Collection#size}, and | |
| 52 | + * {@link Collection#iterator}. Typically, additional methods will be | |
| 53 | + * overridden as well. If these requirements cannot be met, consider | |
| 54 | + * instead subclassing {@link AbstractCollection}. | |
| 55 | + * | |
| 56 | + * <p>This class is a member of the | |
| 57 | + * <a href="{@docRoot}/../technotes/guides/collections/index.html"> | |
| 58 | + * Java Collections Framework</a>. | |
| 59 | + * | |
| 60 | + * @since 1.5 | |
| 61 | + * @author Doug Lea | |
| 62 | + * @param <E> the type of elements held in this collection | |
| 63 | + */ | |
| 64 | +public abstract class AbstractQueue<E> | |
| 65 | + extends AbstractCollection<E> | |
| 66 | + implements Queue<E> { | |
| 67 | + | |
| 68 | + /** | |
| 69 | + * Constructor for use by subclasses. | |
| 70 | + */ | |
| 71 | + protected AbstractQueue() { | |
| 72 | + } | |
| 73 | + | |
| 74 | + /** | |
| 75 | + * Inserts the specified element into this queue if it is possible to do so | |
| 76 | + * immediately without violating capacity restrictions, returning | |
| 77 | + * <tt>true</tt> upon success and throwing an <tt>IllegalStateException</tt> | |
| 78 | + * if no space is currently available. | |
| 79 | + * | |
| 80 | + * <p>This implementation returns <tt>true</tt> if <tt>offer</tt> succeeds, | |
| 81 | + * else throws an <tt>IllegalStateException</tt>. | |
| 82 | + * | |
| 83 | + * @param e the element to add | |
| 84 | + * @return <tt>true</tt> (as specified by {@link Collection#add}) | |
| 85 | + * @throws IllegalStateException if the element cannot be added at this | |
| 86 | + * time due to capacity restrictions | |
| 87 | + * @throws ClassCastException if the class of the specified element | |
| 88 | + * prevents it from being added to this queue | |
| 89 | + * @throws NullPointerException if the specified element is null and | |
| 90 | + * this queue does not permit null elements | |
| 91 | + * @throws IllegalArgumentException if some property of this element | |
| 92 | + * prevents it from being added to this queue | |
| 93 | + */ | |
| 94 | + public boolean add(E e) { | |
| 95 | + if (offer(e)) | |
| 96 | + return true; | |
| 97 | + else | |
| 98 | + throw new IllegalStateException("Queue full"); | |
| 99 | + } | |
| 100 | + | |
| 101 | + /** | |
| 102 | + * Retrieves and removes the head of this queue. This method differs | |
| 103 | + * from {@link #poll poll} only in that it throws an exception if this | |
| 104 | + * queue is empty. | |
| 105 | + * | |
| 106 | + * <p>This implementation returns the result of <tt>poll</tt> | |
| 107 | + * unless the queue is empty. | |
| 108 | + * | |
| 109 | + * @return the head of this queue | |
| 110 | + * @throws NoSuchElementException if this queue is empty | |
| 111 | + */ | |
| 112 | + public E remove() { | |
| 113 | + E x = poll(); | |
| 114 | + if (x != null) | |
| 115 | + return x; | |
| 116 | + else | |
| 117 | + throw new NoSuchElementException(); | |
| 118 | + } | |
| 119 | + | |
| 120 | + /** | |
| 121 | + * Retrieves, but does not remove, the head of this queue. This method | |
| 122 | + * differs from {@link #peek peek} only in that it throws an exception if | |
| 123 | + * this queue is empty. | |
| 124 | + * | |
| 125 | + * <p>This implementation returns the result of <tt>peek</tt> | |
| 126 | + * unless the queue is empty. | |
| 127 | + * | |
| 128 | + * @return the head of this queue | |
| 129 | + * @throws NoSuchElementException if this queue is empty | |
| 130 | + */ | |
| 131 | + public E element() { | |
| 132 | + E x = peek(); | |
| 133 | + if (x != null) | |
| 134 | + return x; | |
| 135 | + else | |
| 136 | + throw new NoSuchElementException(); | |
| 137 | + } | |
| 138 | + | |
| 139 | + /** | |
| 140 | + * Removes all of the elements from this queue. | |
| 141 | + * The queue will be empty after this call returns. | |
| 142 | + * | |
| 143 | + * <p>This implementation repeatedly invokes {@link #poll poll} until it | |
| 144 | + * returns <tt>null</tt>. | |
| 145 | + */ | |
| 146 | + public void clear() { | |
| 147 | + while (poll() != null) | |
| 148 | + ; | |
| 149 | + } | |
| 150 | + | |
| 151 | + /** | |
| 152 | + * Adds all of the elements in the specified collection to this | |
| 153 | + * queue. Attempts to addAll of a queue to itself result in | |
| 154 | + * <tt>IllegalArgumentException</tt>. Further, the behavior of | |
| 155 | + * this operation is undefined if the specified collection is | |
| 156 | + * modified while the operation is in progress. | |
| 157 | + * | |
| 158 | + * <p>This implementation iterates over the specified collection, | |
| 159 | + * and adds each element returned by the iterator to this | |
| 160 | + * queue, in turn. A runtime exception encountered while | |
| 161 | + * trying to add an element (including, in particular, a | |
| 162 | + * <tt>null</tt> element) may result in only some of the elements | |
| 163 | + * having been successfully added when the associated exception is | |
| 164 | + * thrown. | |
| 165 | + * | |
| 166 | + * @param c collection containing elements to be added to this queue | |
| 167 | + * @return <tt>true</tt> if this queue changed as a result of the call | |
| 168 | + * @throws ClassCastException if the class of an element of the specified | |
| 169 | + * collection prevents it from being added to this queue | |
| 170 | + * @throws NullPointerException if the specified collection contains a | |
| 171 | + * null element and this queue does not permit null elements, | |
| 172 | + * or if the specified collection is null | |
| 173 | + * @throws IllegalArgumentException if some property of an element of the | |
| 174 | + * specified collection prevents it from being added to this | |
| 175 | + * queue, or if the specified collection is this queue | |
| 176 | + * @throws IllegalStateException if not all the elements can be added at | |
| 177 | + * this time due to insertion restrictions | |
| 178 | + * @see #add(Object) | |
| 179 | + */ | |
| 180 | + public boolean addAll(Collection<? extends E> c) { | |
| 181 | + if (c == null) | |
| 182 | + throw new NullPointerException(); | |
| 183 | + if (c == this) | |
| 184 | + throw new IllegalArgumentException(); | |
| 185 | + boolean modified = false; | |
| 186 | + for (E e : c) | |
| 187 | + if (add(e)) | |
| 188 | + modified = true; | |
| 189 | + return modified; | |
| 190 | + } | |
| 191 | + | |
| 192 | +} | |