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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 | } | ||