AbstractQueue.java revision 51b1b6997fd3f980076b8081f7f1165ccc2a4008 
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
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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
36package 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 */
64public 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}
193