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Comparing jsr166/src/main/java/util/Queue.java (file contents):
Revision 1.2 by tim, Sun May 18 18:10:02 2003 UTC vs.
Revision 1.38 by jsr166, Wed Jan 16 01:59:47 2013 UTC

#	Line 1 | Line 1
1	+	/*
2	+	* Written by Doug Lea with assistance from members of JCP JSR-166
3	+	* Expert Group and released to the public domain, as explained at
4	+	* http://creativecommons.org/publicdomain/zero/1.0/
5	+	*/
6	+
7		package java.util;
8
9		/**
10	<	* A Collection designed for holding elements prior to processing.
11	<	* Besides basic {@link Collection} operations, queues provide
12	<	* additional insertion, extraction, and inspection operations.
10	>	* A collection designed for holding elements prior to processing.
11	>	* Besides basic {@link java.util.Collection Collection} operations,
12	>	* queues provide additional insertion, extraction, and inspection
13	>	* operations.  Each of these methods exists in two forms: one throws
14	>	* an exception if the operation fails, the other returns a special
15	>	* value (either {@code null} or {@code false}, depending on the
16	>	* operation).  The latter form of the insert operation is designed
17	>	* specifically for use with capacity-restricted {@code Queue}
18	>	* implementations; in most implementations, insert operations cannot
19	>	* fail.
20	>	*
21	>	* <p>
22	>	* <table BORDER CELLPADDING=3 CELLSPACING=1>
23	>	*  <tr>
24	>	*    <td></td>
25	>	*    <td ALIGN=CENTER><em>Throws exception</em></td>
26	>	*    <td ALIGN=CENTER><em>Returns special value</em></td>
27	>	*  </tr>
28	>	*  <tr>
29	>	*    <td><b>Insert</b></td>
30	>	*    <td>{@link #add add(e)}</td>
31	>	*    <td>{@link #offer offer(e)}</td>
32	>	*  </tr>
33	>	*  <tr>
34	>	*    <td><b>Remove</b></td>
35	>	*    <td>{@link #remove remove()}</td>
36	>	*    <td>{@link #poll poll()}</td>
37	>	*  </tr>
38	>	*  <tr>
39	>	*    <td><b>Examine</b></td>
40	>	*    <td>{@link #element element()}</td>
41	>	*    <td>{@link #peek peek()}</td>
42	>	*  </tr>
43	>	* </table>
44		*
45		* <p>Queues typically, but do not necessarily, order elements in a
46	<	* FIFO (first-in-first-out) manner.  Among the exceptions are priority
47	<	* queues, which order elements according to a supplied comparators, or
48	<	* the elements natural ordering.  Every Queue implementation must specify
49	<	* its ordering guarantees.
50	<	*
51	<	* <p>The {@link #offer(E)} method adds an element if possible, otherwise
52	<	* returning <tt>false</tt>.  This differs from the {@link
53	<	* Collections#add(Object)} method, which throws an unchecked exception upon
54	<	* failure. It is designed for use in collections in which failure to
55	<	* add is a normal, rather than exceptional occurrence, for example,
56	<	* in fixed-capacity (or &ldquo;bounded&rdquo;) queues.
57	<	*
58	<	* <p>The {@link #remove()} and {@link #poll()} methods remove and return an
59	<	* element in accord with the implementation's ordering policy. For example,
60	<	* in FIFO queues, they remove and return the oldest element in the queue.
61	<	* The <tt>remove()</tt> and <tt>poll()</tt> methods differ only in their
62	<	* behavior when the queue is empty: the <tt>remove()</tt> method throws an
63	<	* exception, while the <tt>poll()</tt> method returns <tt>null</tt>.
64	<	*
65	<	* <p>The {@link #element()} and {@link #peek()} methods return but do
66	<	* not delete the element that would be obtained by a call to
67	<	* the <tt>remove</tt> and <tt>poll</tt> methods respectively.
46	>	* FIFO (first-in-first-out) manner.  Among the exceptions are
47	>	* priority queues, which order elements according to a supplied
48	>	* comparator, or the elements' natural ordering, and LIFO queues (or
49	>	* stacks) which order the elements LIFO (last-in-first-out).
50	>	* Whatever the ordering used, the <em>head</em> of the queue is that
51	>	* element which would be removed by a call to {@link #remove() } or
52	>	* {@link #poll()}.  In a FIFO queue, all new elements are inserted at
53	>	* the <em>tail</em> of the queue. Other kinds of queues may use
54	>	* different placement rules.  Every {@code Queue} implementation
55	>	* must specify its ordering properties.
56	>	*
57	>	* <p>The {@link #offer offer} method inserts an element if possible,
58	>	* otherwise returning {@code false}.  This differs from the {@link
59	>	* java.util.Collection#add Collection.add} method, which can fail to
60	>	* add an element only by throwing an unchecked exception.  The
61	>	* {@code offer} method is designed for use when failure is a normal,
62	>	* rather than exceptional occurrence, for example, in fixed-capacity
63	>	* (or &quot;bounded&quot;) queues.
64	>	*
65	>	* <p>The {@link #remove()} and {@link #poll()} methods remove and
66	>	* return the head of the queue.
67	>	* Exactly which element is removed from the queue is a
68	>	* function of the queue's ordering policy, which differs from
69	>	* implementation to implementation. The {@code remove()} and
70	>	* {@code poll()} methods differ only in their behavior when the
71	>	* queue is empty: the {@code remove()} method throws an exception,
72	>	* while the {@code poll()} method returns {@code null}.
73	>	*
74	>	* <p>The {@link #element()} and {@link #peek()} methods return, but do
75	>	* not remove, the head of the queue.
76		*
77	<	* <p>The <tt>Queue</tt> interface does not define the <i>blocking queue
77	>	* <p>The {@code Queue} interface does not define the <i>blocking queue
78		* methods</i>, which are common in concurrent programming.  These methods,
79		* which wait for elements to appear or for space to become available, are
80		* defined in the {@link java.util.concurrent.BlockingQueue} interface, which
81		* extends this interface.
82		*
83	<	* <p><tt>Queue</tt> implementations generally do not allow insertion of
84	<	* <tt>null</tt> elements.  Even in the few implementations that permit it,
85	<	* it is a bad idea, as <tt>null</tt> is also used as a special return value
86	<	* by the <tt>poll</tt> method to indicate that the queue contains no
87	<	* elements.
83	>	* <p>{@code Queue} implementations generally do not allow insertion
84	>	* of {@code null} elements, although some implementations, such as
85	>	* {@link LinkedList}, do not prohibit insertion of {@code null}.
86	>	* Even in the implementations that permit it, {@code null} should
87	>	* not be inserted into a {@code Queue}, as {@code null} is also
88	>	* used as a special return value by the {@code poll} method to
89	>	* indicate that the queue contains no elements.
90	>	*
91	>	* <p>{@code Queue} implementations generally do not define
92	>	* element-based versions of methods {@code equals} and
93	>	* {@code hashCode} but instead inherit the identity based versions
94	>	* from class {@code Object}, because element-based equality is not
95	>	* always well-defined for queues with the same elements but different
96	>	* ordering properties.
97	>	*
98		*
99		* <p>This interface is a member of the
100	<	* <a href="{@docRoot}/../guide/collections/index.html">
100	>	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
101		* Java Collections Framework</a>.
102		*
103	<	* @see Collection
103	>	* @see java.util.Collection
104		* @see LinkedList
105		* @see PriorityQueue
106	<	* @see LinkedQueue
106	>	* @see java.util.concurrent.LinkedBlockingQueue
107		* @see java.util.concurrent.BlockingQueue
108		* @see java.util.concurrent.ArrayBlockingQueue
109		* @see java.util.concurrent.LinkedBlockingQueue
110		* @see java.util.concurrent.PriorityBlockingQueue
111	+	* @since 1.5
112	+	* @author Doug Lea
113	+	* @param <E> the type of elements held in this collection
114		*/
115		public interface Queue<E> extends Collection<E> {
116		/**
117	<	* Add the specified element to this queue, if possible.
117	>	* Inserts the specified element into this queue if it is possible to do so
118	>	* immediately without violating capacity restrictions, returning
119	>	* {@code true} upon success and throwing an {@code IllegalStateException}
120	>	* if no space is currently available.
121		*
122	<	* @param element the element to add.
123	<	* @return true if it was possible to add the element to the queue.
122	>	* @param e the element to add
123	>	* @return {@code true} (as specified by {@link Collection#add})
124	>	* @throws IllegalStateException if the element cannot be added at this
125	>	*         time due to capacity restrictions
126	>	* @throws ClassCastException if the class of the specified element
127	>	*         prevents it from being added to this queue
128	>	* @throws NullPointerException if the specified element is null and
129	>	*         this queue does not permit null elements
130	>	* @throws IllegalArgumentException if some property of this element
131	>	*         prevents it from being added to this queue
132		*/
133	<	public boolean offer(E element);
133	>	boolean add(E e);
134
135		/**
136	<	* Remove and return an element from the queue if one is available.
137	<	* Exactly which element is removed from the queue is a function
138	<	* of the queue's ordering policy, which differs from implementation
139	<	* to implementation.  Possible orderings include (but are not limited
140	<	* to) first-in-first-out (FIFO), element priority, and arbitrary.
136	>	* Inserts the specified element into this queue if it is possible to do
137	>	* so immediately without violating capacity restrictions.
138	>	* When using a capacity-restricted queue, this method is generally
139	>	* preferable to {@link #add}, which can fail to insert an element only
140	>	* by throwing an exception.
141		*
142	<	* @return an element previously on the queue, or <tt>null</tt> if the
143	<	*         queue is empty.
142	>	* @param e the element to add
143	>	* @return {@code true} if the element was added to this queue, else
144	>	*         {@code false}
145	>	* @throws ClassCastException if the class of the specified element
146	>	*         prevents it from being added to this queue
147	>	* @throws NullPointerException if the specified element is null and
148	>	*         this queue does not permit null elements
149	>	* @throws IllegalArgumentException if some property of this element
150	>	*         prevents it from being added to this queue
151		*/
152	<	public E poll();
152	>	boolean offer(E e);
153
154		/**
155	<	* Remove and return an element from the queue.  This method differs
156	<	* from the <tt>poll</tt> method in that it throws an exception if the
155	>	* Retrieves and removes the head of this queue.  This method differs
156	>	* from {@link #poll poll} only in that it throws an exception if this
157		* queue is empty.
158		*
159	<	* @return an element previously on the queue.
160	<	* @throws NoSuchElementException if the queue is empty.
159	>	* @return the head of this queue
160	>	* @throws NoSuchElementException if this queue is empty
161	>	*/
162	>	E remove();
163	>
164	>	/**
165	>	* Retrieves and removes the head of this queue,
166	>	* or returns {@code null} if this queue is empty.
167	>	*
168	>	* @return the head of this queue, or {@code null} if this queue is empty
169		*/
170	<	public E remove() throws NoSuchElementException;
170	>	E poll();
171
172		/**
173	<	* Return, but do not remove, an element from the queue, or <tt>null</tt>
174	<	* if the queue is empty.  This method returns the same object reference
175	<	* that would be returned by by the <tt>poll</tt> method.  The two methods
92	<	* differ in that this method does not remove the element from the queue.
173	>	* Retrieves, but does not remove, the head of this queue.  This method
174	>	* differs from {@link #peek peek} only in that it throws an exception
175	>	* if this queue is empty.
176		*
177	<	* @return an element on the queue, or <tt>null</tt> if the queue is empty.
177	>	* @return the head of this queue
178	>	* @throws NoSuchElementException if this queue is empty
179		*/
180	<	public E peek();
180	>	E element();
181
182		/**
183	<	* Return, but do not remove, an element from the queue.  This method
184	<	* differs from the <tt>peek</tt> method in that it throws an exception if
101	<	* the queue is empty.
183	>	* Retrieves, but does not remove, the head of this queue,
184	>	* or returns {@code null} if this queue is empty.
185		*
186	<	* @return an element on the queue.
104	<	* @throws NoSuchElementException if the queue is empty.
186	>	* @return the head of this queue, or {@code null} if this queue is empty
187		*/
188	<	public E element() throws NoSuchElementException;
188	>	E peek();
189		}

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