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 {@code null}
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 {@code false} or
46 * {@code null} returns.
47 *
48 * <p>A {@code Queue} implementation that extends this class must
49 * minimally define a method {@link Queue#offer} which does not permit
50 * insertion of {@code null} 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 * {@code true} upon success and throwing an {@code IllegalStateException}
78 * if no space is currently available.
79 *
80 * <p>This implementation returns {@code true} if {@code offer} succeeds,
81 * else throws an {@code IllegalStateException}.
82 *
83 * @param e the element to add
84 * @return {@code true} (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 {@code poll}
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 {@code peek}
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 {@code null}.
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 * {@code IllegalArgumentException}. 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 * {@code null} 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 {@code true} 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 }