AbstractQueue.java revision 5328e07d282bef36ac8b757bbee16a761415b2c4 
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.
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20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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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 * Written by Doug Lea with assistance from members of JCP JSR-166
31 * Expert Group and released to the public domain, as explained at
32 * http://creativecommons.org/publicdomain/zero/1.0/
33 */
34
35package java.util;
36
37// BEGIN android-note
38// removed link to collections framework docs
39// END android-note
40
41/**
42 * This class provides skeletal implementations of some {@link Queue}
43 * operations. The implementations in this class are appropriate when
44 * the base implementation does <em>not</em> allow {@code null}
45 * elements.  Methods {@link #add add}, {@link #remove remove}, and
46 * {@link #element element} are based on {@link #offer offer}, {@link
47 * #poll poll}, and {@link #peek peek}, respectively, but throw
48 * exceptions instead of indicating failure via {@code false} or
49 * {@code null} returns.
50 *
51 * <p>A {@code Queue} implementation that extends this class must
52 * minimally define a method {@link Queue#offer} which does not permit
53 * insertion of {@code null} elements, along with methods {@link
54 * Queue#peek}, {@link Queue#poll}, {@link Collection#size}, and
55 * {@link Collection#iterator}.  Typically, additional methods will be
56 * overridden as well.  If these requirements cannot be met, consider
57 * instead subclassing {@link AbstractCollection}.
58 *
59 * @since 1.5
60 * @author Doug Lea
61 * @param <E> the type of elements held in this queue
62 */
63public abstract class AbstractQueue<E>
64    extends AbstractCollection<E>
65    implements Queue<E> {
66
67    /**
68     * Constructor for use by subclasses.
69     */
70    protected AbstractQueue() {
71    }
72
73    /**
74     * Inserts the specified element into this queue if it is possible to do so
75     * immediately without violating capacity restrictions, returning
76     * {@code true} upon success and throwing an {@code IllegalStateException}
77     * if no space is currently available.
78     *
79     * <p>This implementation returns {@code true} if {@code offer} succeeds,
80     * else throws an {@code IllegalStateException}.
81     *
82     * @param e the element to add
83     * @return {@code true} (as specified by {@link Collection#add})
84     * @throws IllegalStateException if the element cannot be added at this
85     *         time due to capacity restrictions
86     * @throws ClassCastException if the class of the specified element
87     *         prevents it from being added to this queue
88     * @throws NullPointerException if the specified element is null and
89     *         this queue does not permit null elements
90     * @throws IllegalArgumentException if some property of this element
91     *         prevents it from being added to this queue
92     */
93    public boolean add(E e) {
94        if (offer(e))
95            return true;
96        else
97            throw new IllegalStateException("Queue full");
98    }
99
100    /**
101     * Retrieves and removes the head of this queue.  This method differs
102     * from {@link #poll poll} only in that it throws an exception if this
103     * queue is empty.
104     *
105     * <p>This implementation returns the result of {@code poll}
106     * unless the queue is empty.
107     *
108     * @return the head of this queue
109     * @throws NoSuchElementException if this queue is empty
110     */
111    public E remove() {
112        E x = poll();
113        if (x != null)
114            return x;
115        else
116            throw new NoSuchElementException();
117    }
118
119    /**
120     * Retrieves, but does not remove, the head of this queue.  This method
121     * differs from {@link #peek peek} only in that it throws an exception if
122     * this queue is empty.
123     *
124     * <p>This implementation returns the result of {@code peek}
125     * unless the queue is empty.
126     *
127     * @return the head of this queue
128     * @throws NoSuchElementException if this queue is empty
129     */
130    public E element() {
131        E x = peek();
132        if (x != null)
133            return x;
134        else
135            throw new NoSuchElementException();
136    }
137
138    /**
139     * Removes all of the elements from this queue.
140     * The queue will be empty after this call returns.
141     *
142     * <p>This implementation repeatedly invokes {@link #poll poll} until it
143     * returns {@code null}.
144     */
145    public void clear() {
146        while (poll() != null)
147            ;
148    }
149
150    /**
151     * Adds all of the elements in the specified collection to this
152     * queue.  Attempts to addAll of a queue to itself result in
153     * {@code IllegalArgumentException}. Further, the behavior of
154     * this operation is undefined if the specified collection is
155     * modified while the operation is in progress.
156     *
157     * <p>This implementation iterates over the specified collection,
158     * and adds each element returned by the iterator to this
159     * queue, in turn.  A runtime exception encountered while
160     * trying to add an element (including, in particular, a
161     * {@code null} element) may result in only some of the elements
162     * having been successfully added when the associated exception is
163     * thrown.
164     *
165     * @param c collection containing elements to be added to this queue
166     * @return {@code true} if this queue changed as a result of the call
167     * @throws ClassCastException if the class of an element of the specified
168     *         collection prevents it from being added to this queue
169     * @throws NullPointerException if the specified collection contains a
170     *         null element and this queue does not permit null elements,
171     *         or if the specified collection is null
172     * @throws IllegalArgumentException if some property of an element of the
173     *         specified collection prevents it from being added to this
174     *         queue, or if the specified collection is this queue
175     * @throws IllegalStateException if not all the elements can be added at
176     *         this time due to insertion restrictions
177     * @see #add(Object)
178     */
179    public boolean addAll(Collection<? extends E> c) {
180        if (c == null)
181            throw new NullPointerException();
182        if (c == this)
183            throw new IllegalArgumentException();
184        boolean modified = false;
185        for (E e : c)
186            if (add(e))
187                modified = true;
188        return modified;
189    }
190
191}
192