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
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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
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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 
36 package java.util;
37 
38 // BEGIN android-note
39 // removed link to collections framework docs
40 // END android-note
41 
42 /**
43  * This class provides skeletal implementations of some {@link Queue}
44  * operations. The implementations in this class are appropriate when
45  * the base implementation does <em>not</em> allow {@code null}
46  * elements.  Methods {@link #add add}, {@link #remove remove}, and
47  * {@link #element element} are based on {@link #offer offer}, {@link
48  * #poll poll}, and {@link #peek peek}, respectively, but throw
49  * exceptions instead of indicating failure via {@code false} or
50  * {@code null} returns.
51  *
52  * <p>A {@code Queue} implementation that extends this class must
53  * minimally define a method {@link Queue#offer} which does not permit
54  * insertion of {@code null} elements, along with methods {@link
55  * Queue#peek}, {@link Queue#poll}, {@link Collection#size}, and
56  * {@link Collection#iterator}.  Typically, additional methods will be
57  * overridden as well.  If these requirements cannot be met, consider
58  * instead subclassing {@link AbstractCollection}.
59  *
60  * @since 1.5
61  * @author Doug Lea
62  * @param <E> the type of elements held in this queue
63  */
64 public abstract class AbstractQueue<E>
65     extends AbstractCollection<E>
66     implements Queue<E> {
67 
68     /**
69      * Constructor for use by subclasses.
70      */
AbstractQueue()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      */
add(E e)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      */
remove()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      */
element()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      */
clear()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      */
addAll(Collection<? extends E> c)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