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Comparing jsr166/src/main/java/util/Queue.java (file contents):
Revision 1.1 by tim, Wed May 14 21:30:45 2003 UTC vs.
Revision 1.45 by jsr166, Wed Apr 19 23:45:50 2017 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	<	* Queues are Collections supporting additional basic insertion,
11	<	* extraction, and inspection operations.
12	<	*
13	<	* <p> Queues typically, but do not necessarily order elements in a
14	<	* FIFO (first-in-first-out) manner. Among the exceptions are priority
15	<	* queues, that order elements in accord with supplied
16	<	* Comparators. Every Queue implementation must specify its ordering
17	<	* guarantees,
18	<	*
19	<	* <p> The <tt>offer</tt> method adds an element if possible,
20	<	* otherwise returning <tt>false</tt>. This differs from the
21	<	* Collections.add method, that throws an unchecked exception upon
22	<	* failure. It is designed for use in collections in which failure to
23	<	* add is a normal, rather than exceptional occurrence, for example,
24	<	* in fixed-capacity queues.
25	<	*
26	<	* <p> The <tt>remove</tt> and <tt>poll</tt> methods delete and return
27	<	* an element in accord with the implementation's ordering policies --
28	<	* for example, in FIFO queues, it will return the oldest element.
29	<	* The <tt>remove</tt> and <tt>poll</tt> differ only in their behavior
30	<	* when the queue is empty: <tt>poll</tt> returns <tt>null</tt> while
31	<	* <tt>remove</tt> throws an exception. These are designed for usage
32	<	* contexts in which emptiness is considered to be normal versus
33	<	* exceptional.
34	<	*
35	<	* <p> The <tt>element</tt> and <tt>peek</tt> methods return but do
36	<	* not delete the element that would be obtained by a call to
37	<	* <tt>remove</tt> and <tt>poll</tt> respectively.
38	<	*
39	<	* <p> The Queue interface does not define blocking queue methods
40	<	* (i.e., those that wait for elements to appear and/or for space to
41	<	* be available) that are common in concurrent programming. These are
42	<	* defined in the extended java.util.concurrent.BlockingQueue
43	<	* interface.
44	<	*
45	<	* <p> Queue implementations generally do not allow insertion of
46	<	* <tt>null</tt>. Even in those that allow it, it is a very bad idea
47	<	* to do so, since <tt>null</tt> is also used as a sentinel by
48	<	* <tt>poll</tt> to indicate that no elements exist.
49	<	**/
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.
13	>	* Each of these methods exists in two forms: one throws an exception
14	>	* if the operation fails, the other returns a special value (either
15	>	* {@code null} or {@code false}, depending on the operation).  The
16	>	* latter form of the insert operation is designed specifically for
17	>	* use with capacity-restricted {@code Queue} implementations; in most
18	>	* implementations, insert operations cannot fail.
19	>	*
20	>	* <table BORDER CELLPADDING=3 CELLSPACING=1>
21	>	* <caption>Summary of Queue methods</caption>
22	>	*  <tr>
23	>	*    <td></td>
24	>	*    <td ALIGN=CENTER><em>Throws exception</em></td>
25	>	*    <td ALIGN=CENTER><em>Returns special value</em></td>
26	>	*  </tr>
27	>	*  <tr>
28	>	*    <td><b>Insert</b></td>
29	>	*    <td>{@link #add(Object) add(e)}</td>
30	>	*    <td>{@link #offer(Object) offer(e)}</td>
31	>	*  </tr>
32	>	*  <tr>
33	>	*    <td><b>Remove</b></td>
34	>	*    <td>{@link #remove() remove()}</td>
35	>	*    <td>{@link #poll() poll()}</td>
36	>	*  </tr>
37	>	*  <tr>
38	>	*    <td><b>Examine</b></td>
39	>	*    <td>{@link #element() element()}</td>
40	>	*    <td>{@link #peek() peek()}</td>
41	>	*  </tr>
42	>	* </table>
43	>	*
44	>	* <p>Queues typically, but do not necessarily, order elements in a
45	>	* FIFO (first-in-first-out) manner.  Among the exceptions are
46	>	* priority queues, which order elements according to a supplied
47	>	* comparator, or the elements' natural ordering, and LIFO queues (or
48	>	* stacks) which order the elements LIFO (last-in-first-out).
49	>	* Whatever the ordering used, the <em>head</em> of the queue is that
50	>	* element which would be removed by a call to {@link #remove()} or
51	>	* {@link #poll()}.  In a FIFO queue, all new elements are inserted at
52	>	* the <em>tail</em> of the queue. Other kinds of queues may use
53	>	* different placement rules.  Every {@code Queue} implementation
54	>	* must specify its ordering properties.
55	>	*
56	>	* <p>The {@link #offer offer} method inserts an element if possible,
57	>	* otherwise returning {@code false}.  This differs from the {@link
58	>	* java.util.Collection#add Collection.add} method, which can fail to
59	>	* add an element only by throwing an unchecked exception.  The
60	>	* {@code offer} method is designed for use when failure is a normal,
61	>	* rather than exceptional occurrence, for example, in fixed-capacity
62	>	* (or &quot;bounded&quot;) queues.
63	>	*
64	>	* <p>The {@link #remove()} and {@link #poll()} methods remove and
65	>	* return the head of the queue.
66	>	* Exactly which element is removed from the queue is a
67	>	* function of the queue's ordering policy, which differs from
68	>	* implementation to implementation. The {@code remove()} and
69	>	* {@code poll()} methods differ only in their behavior when the
70	>	* queue is empty: the {@code remove()} method throws an exception,
71	>	* while the {@code poll()} method returns {@code null}.
72	>	*
73	>	* <p>The {@link #element()} and {@link #peek()} methods return, but do
74	>	* not remove, the head of the queue.
75	>	*
76	>	* <p>The {@code Queue} interface does not define the <i>blocking queue
77	>	* methods</i>, which are common in concurrent programming.  These methods,
78	>	* which wait for elements to appear or for space to become available, are
79	>	* defined in the {@link java.util.concurrent.BlockingQueue} interface, which
80	>	* extends this interface.
81	>	*
82	>	* <p>{@code Queue} implementations generally do not allow insertion
83	>	* of {@code null} elements, although some implementations, such as
84	>	* {@link LinkedList}, do not prohibit insertion of {@code null}.
85	>	* Even in the implementations that permit it, {@code null} should
86	>	* not be inserted into a {@code Queue}, as {@code null} is also
87	>	* used as a special return value by the {@code poll} method to
88	>	* indicate that the queue contains no elements.
89	>	*
90	>	* <p>{@code Queue} implementations generally do not define
91	>	* element-based versions of methods {@code equals} and
92	>	* {@code hashCode} but instead inherit the identity based versions
93	>	* from class {@code Object}, because element-based equality is not
94	>	* always well-defined for queues with the same elements but different
95	>	* ordering properties.
96	>	*
97	>	* <p>This interface is a member of the
98	>	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
99	>	* Java Collections Framework</a>.
100	>	*
101	>	* @since 1.5
102	>	* @author Doug Lea
103	>	* @param <E> the type of elements held in this queue
104	>	*/
105		public interface Queue<E> extends Collection<E> {
106	+	/**
107	+	* Inserts the specified element into this queue if it is possible to do so
108	+	* immediately without violating capacity restrictions, returning
109	+	* {@code true} upon success and throwing an {@code IllegalStateException}
110	+	* if no space is currently available.
111	+	*
112	+	* @param e the element to add
113	+	* @return {@code true} (as specified by {@link Collection#add})
114	+	* @throws IllegalStateException if the element cannot be added at this
115	+	*         time due to capacity restrictions
116	+	* @throws ClassCastException if the class of the specified element
117	+	*         prevents it from being added to this queue
118	+	* @throws NullPointerException if the specified element is null and
119	+	*         this queue does not permit null elements
120	+	* @throws IllegalArgumentException if some property of this element
121	+	*         prevents it from being added to this queue
122	+	*/
123	+	boolean add(E e);
124	+
125	+	/**
126	+	* Inserts the specified element into this queue if it is possible to do
127	+	* so immediately without violating capacity restrictions.
128	+	* When using a capacity-restricted queue, this method is generally
129	+	* preferable to {@link #add}, which can fail to insert an element only
130	+	* by throwing an exception.
131	+	*
132	+	* @param e the element to add
133	+	* @return {@code true} if the element was added to this queue, else
134	+	*         {@code false}
135	+	* @throws ClassCastException if the class of the specified element
136	+	*         prevents it from being added to this queue
137	+	* @throws NullPointerException if the specified element is null and
138	+	*         this queue does not permit null elements
139	+	* @throws IllegalArgumentException if some property of this element
140	+	*         prevents it from being added to this queue
141	+	*/
142	+	boolean offer(E e);
143	+
144	+	/**
145	+	* Retrieves and removes the head of this queue.  This method differs
146	+	* from {@link #poll() poll()} only in that it throws an exception if
147	+	* this queue is empty.
148	+	*
149	+	* @return the head of this queue
150	+	* @throws NoSuchElementException if this queue is empty
151	+	*/
152	+	E remove();
153	+
154	+	/**
155	+	* Retrieves and removes the head of this queue,
156	+	* or returns {@code null} if this queue is empty.
157	+	*
158	+	* @return the head of this queue, or {@code null} if this queue is empty
159	+	*/
160	+	E poll();
161	+
162	+	/**
163	+	* Retrieves, but does not remove, the head of this queue.  This method
164	+	* differs from {@link #peek peek} only in that it throws an exception
165	+	* if this queue is empty.
166	+	*
167	+	* @return the head of this queue
168	+	* @throws NoSuchElementException if this queue is empty
169	+	*/
170	+	E element();
171
172		/**
173	<	* Add the given object to this queue if possible.
174	<	* @param x the object to add
175	<	* @return true if successful
176	<	**/
177	<	public boolean offer(E x);
178	<
53	<	/**
54	<	* Delete and return an object from the queue if one is available.
55	<	* @return the object, or null if the queue is empty.
56	<	**/
57	<	public E poll();
58	<
59	<	/**
60	<	* Delete and return the element produced by poll, if the queue is
61	<	* not empty.
62	<	* @return an element
63	<	* @throws NoSuchElementException if empty
64	<	**/
65	<	public E remove() throws NoSuchElementException;
66	<
67	<	/**
68	<	* Return but do not delete the element that will be returned by
69	<	* the next call to poll.
70	<	* @return an element, or null if empty
71	<	**/
72	<	public E peek();
73	<
74	<	/**
75	<	* Return but do not delete the element that will be returned by
76	<	* the next call to poll, if the queue is not empty.
77	<	* @return an element
78	<	* @throws NoSuchElementException if empty
79	<	**/
80	<	public E element() throws NoSuchElementException;
173	>	* Retrieves, but does not remove, the head of this queue,
174	>	* or returns {@code null} if this queue is empty.
175	>	*
176	>	* @return the head of this queue, or {@code null} if this queue is empty
177	>	*/
178	>	E peek();
179		}

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