| AbstractQueue.java |
1 /*
2 * %W% %E%
3 *
4 * Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved.
5 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6 */
7
8 package java.util;
9
10 /**
11 * This class provides skeletal implementations of some {@link Queue}
12 * operations. The implementations in this class are appropriate when
13 * the base implementation does <em>not</em> allow <tt>null</tt>
14 * elements. Methods {@link #add add}, {@link #remove remove}, and
15 * {@link #element element} are based on {@link #offer offer}, {@link
16 * #poll poll}, and {@link #peek peek}, respectively but throw
17 * exceptions instead of indicating failure via <tt>false</tt> or
18 * <tt>null</tt> returns.
19 *
20 * <p> A <tt>Queue</tt> implementation that extends this class must
21 * minimally define a method {@link Queue#offer} which does not permit
22 * insertion of <tt>null</tt> elements, along with methods {@link
23 * Queue#peek}, {@link Queue#poll}, {@link Collection#size}, and a
24 * {@link Collection#iterator} supporting {@link
25 * Iterator#remove}. Typically, additional methods will be overridden
26 * as well. If these requirements cannot be met, consider instead
27 * subclassing {@link AbstractCollection}.
28 *
29 * <p>This class is a member of the
30 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
31 * Java Collections Framework</a>.
32 *
33 * @since 1.5
34 * @author Doug Lea
35 * @param <E> the type of elements held in this collection
36 */
37 public abstract class AbstractQueue<E>
38 extends AbstractCollection<E>
39 implements Queue<E> {
40
41 /**
42 * Constructor for use by subclasses.
43 */
44 protected AbstractQueue() {
45 }
46
47 /**
48 * Inserts the specified element into this queue if it is possible to do so
49 * immediately without violating capacity restrictions, returning
50 * <tt>true</tt> upon success and throwing an <tt>IllegalStateException</tt>
51 * if no space is currently available.
52 *
53 * <p>This implementation returns <tt>true</tt> if <tt>offer</tt> succeeds,
54 * else throws an <tt>IllegalStateException</tt>.
55 *
56 * @param e the element to add
57 * @return <tt>true</tt> (as specified by {@link Collection#add})
58 * @throws IllegalStateException if the element cannot be added at this
59 * time due to capacity restrictions
60 * @throws ClassCastException if the class of the specified element
61 * prevents it from being added to this queue
62 * @throws NullPointerException if the specified element is null and
63 * this queue does not permit null elements
64 * @throws IllegalArgumentException if some property of this element
65 * prevents it from being added to this queue
66 */
67 public boolean add(E e) {
68 if (offer(e))
69 return true;
70 else
71 throw new IllegalStateException("Queue full");
72 }
73
74 /**
75 * Retrieves and removes the head of this queue. This method differs
76 * from {@link #poll poll} only in that it throws an exception if this
77 * queue is empty.
78 *
79 * <p>This implementation returns the result of <tt>poll</tt>
80 * unless the queue is empty.
81 *
82 * @return the head of this queue
83 * @throws NoSuchElementException if this queue is empty
84 */
85 public E remove() {
86 E x = poll();
87 if (x != null)
88 return x;
89 else
90 throw new NoSuchElementException();
91 }
92
93 /**
94 * Retrieves, but does not remove, the head of this queue. This method
95 * differs from {@link #peek peek} only in that it throws an exception if
96 * this queue is empty.
97 *
98 * <p>This implementation returns the result of <tt>peek</tt>
99 * unless the queue is empty.
100 *
101 * @return the head of this queue
102 * @throws NoSuchElementException if this queue is empty
103 */
104 public E element() {
105 E x = peek();
106 if (x != null)
107 return x;
108 else
109 throw new NoSuchElementException();
110 }
111
112 /**
113 * Removes all of the elements from this queue.
114 * The queue will be empty after this call returns.
115 *
116 * <p>This implementation repeatedly invokes {@link #poll poll} until it
117 * returns <tt>null</tt>.
118 */
119 public void clear() {
120 while (poll() != null)
121 ;
122 }
123
124 /**
125 * Adds all of the elements in the specified collection to this
126 * queue. Attempts to addAll of a queue to itself result in
127 * <tt>IllegalArgumentException</tt>. Further, the behavior of
128 * this operation is undefined if the specified collection is
129 * modified while the operation is in progress.
130 *
131 * <p>This implementation iterates over the specified collection,
132 * and adds each element returned by the iterator to this
133 * queue, in turn. A runtime exception encountered while
134 * trying to add an element (including, in particular, a
135 * <tt>null</tt> element) may result in only some of the elements
136 * having been successfully added when the associated exception is
137 * thrown.
138 *
139 * @param c collection containing elements to be added to this queue
140 * @return <tt>true</tt> if this queue changed as a result of the call
141 * @throws ClassCastException if the class of an element of the specified
142 * collection prevents it from being added to this queue
143 * @throws NullPointerException if the specified collection contains a
144 * null element and this queue does not permit null elements,
145 * or if the specified collection is null
146 * @throws IllegalArgumentException if some property of an element of the
147 * specified collection prevents it from being added to this
148 * queue, or if the specified collection is this queue
149 * @throws IllegalStateException if not all the elements can be added at
150 * this time due to insertion restrictions
151 * @see #add(Object)
152 */
153 public boolean addAll(Collection<? extends E> c) {
154 if (c == null)
155 throw new NullPointerException();
156 if (c == this)
157 throw new IllegalArgumentException();
158 boolean modified = false;
159 Iterator<? extends E> e = c.iterator();
160 while (e.hasNext()) {
161 if (add(e.next()))
162 modified = true;
163 }
164 return modified;
165 }
166
167 }
168