ViewVC Help

View File | Revision Log | Show Annotations | Download File | Root Listing

root/jsr166/jsr166/src/main/java/util/Queue.java

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 1.7 by dl, Tue Jun 24 14:34:30 2003 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. Use, modify, and
4	+	* redistribute this code in any way without acknowledgement.
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
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	>	0 *
14	>	* <p>Queues typically, but do not necessarily, order elements in a
15	>	* FIFO (first-in-first-out) manner.  Among the exceptions are
16	>	* priority queues, which order elements according to a supplied
17	>	* comparator, or the elements' natural ordering.  Every Queue
18	>	* implementation must specify its ordering guarantees.
19	>	*
20	>	* <p>The {@link #offer(E)} method adds an element if possible, otherwise
21	>	* returning <tt>false</tt>.  This differs from the {@link
22	>	* Collections#add(Object)} method, which throws an unchecked exception upon
23		* failure. It is designed for use in collections in which failure to
24		* add is a normal, rather than exceptional occurrence, for example,
25	<	* in fixed-capacity queues.
26	<	*
27	<	* <p> The <tt>remove</tt> and <tt>poll</tt> methods delete and return
28	<	* an element in accord with the implementation's ordering policies --
29	<	* for example, in FIFO queues, it will return the oldest element.
30	<	* The <tt>remove</tt> and <tt>poll</tt> differ only in their behavior
31	<	* when the queue is empty: <tt>poll</tt> returns <tt>null</tt> while
32	<	* <tt>remove</tt> throws an exception. These are designed for usage
33	<	* contexts in which emptiness is considered to be normal versus
34	<	* exceptional.
25	>	* in fixed-capacity (or &ldquo;bounded&rdquo;) queues.
26	>
27	>	*
28	>	* <p>The {@link #remove()} and {@link #poll()} methods remove and
29	>	* return an element in accord with the implementation's ordering
30	>	* policy.  Exactly which element is removed from the queue is a
31	>	* function of the queue's ordering policy, which differs from
32	>	* implementation to implementation.  Possible orderings include (but
33	>	* are not limited to) first-in-first-out (FIFO), last-in-first-out
34	>	* (LIFO), element priority, and arbitrary.  The <tt>remove()</tt> and
35	>	* <tt>poll()</tt> methods differ only in their behavior when the
36	>	* queue is empty: the <tt>remove()</tt> method throws an exception,
37	>	* while the <tt>poll()</tt> method returns <tt>null</tt>.
38		*
39	<	* <p> The <tt>element</tt> and <tt>peek</tt> methods return but do
39	>	* <p>The {@link #element()} and {@link #peek()} methods return but do
40		* not delete the element that would be obtained by a call to
41	<	* <tt>remove</tt> and <tt>poll</tt> respectively.
41	>	* the <tt>remove</tt> and <tt>poll</tt> methods respectively.
42		*
43	<	* <p> The Queue interface does not define blocking queue methods
44	<	* (i.e., those that wait for elements to appear and/or for space to
45	<	* be available) that are common in concurrent programming. These are
46	<	* defined in the extended java.util.concurrent.BlockingQueue
47	<	* interface.
48	<	*
49	<	* <p> Queue implementations generally do not allow insertion of
50	<	* <tt>null</tt>. Even in those that allow it, it is a very bad idea
51	<	* to do so, since <tt>null</tt> is also used as a sentinel by
52	<	* <tt>poll</tt> to indicate that no elements exist.
53	<	**/
43	>	* <p>The <tt>Queue</tt> interface does not define the <i>blocking queue
44	>	* methods</i>, which are common in concurrent programming.  These methods,
45	>	* which wait for elements to appear or for space to become available, are
46	>	* defined in the {@link java.util.concurrent.BlockingQueue} interface, which
47	>	* extends this interface.
48	>	*
49	>	* <p><tt>Queue</tt> implementations generally do not allow insertion
50	>	* of <tt>null</tt> elements, although some implementations, such as
51	>	* {@link LinkedList}, do not prohibit insertion of <tt>null</tt>.
52	>	* Even in the implementations that permit it, <tt>null</tt> should
53	>	* not be inserted into a <tt>Queue</tt>, as <tt>null</tt> is also
54	>	* used as a special return value by the <tt>poll</tt> method to
55	>	* indicate that the queue contains no elements.
56	>	*
57	>	* <p>This interface is a member of the
58	>	* <a href="{@docRoot}/../guide/collections/index.html">
59	>	* Java Collections Framework</a>.
60	>	*
61	>	* @see Collection
62	>	* @see LinkedList
63	>	* @see PriorityQueue
64	>	* @see java.util.concurrent.LinkedQueue
65	>	* @see java.util.concurrent.BlockingQueue
66	>	* @see java.util.concurrent.ArrayBlockingQueue
67	>	* @see java.util.concurrent.LinkedBlockingQueue
68	>	* @see java.util.concurrent.PriorityBlockingQueue
69	>	* @since 1.5
70	>	* @author Doug Lea
71	>	*/
72		public interface Queue<E> extends Collection<E> {
45	–
73		/**
74	<	* Add the given object to this queue if possible.
75	<	* @param x the object to add
76	<	* @return true if successful
77	<	**/
78	<	public boolean offer(E x);
74	>	* Add the specified element to this queue, if possible.
75	>	*
76	>	* @param element the element to add.
77	>	* @return true if it was possible to add the element to the queue.
78	>	*/
79	>	boolean offer(E element);
80
81		/**
82	<	* Delete and return an object from the queue if one is available.
83	<	* @return the object, or null if the queue is empty.
84	<	**/
85	<	public E poll();
82	>	* Remove and return an element from the queue if one is available.
83	>	*
84	>	* @return an element previously on the queue, or <tt>null</tt> if the
85	>	*         queue is empty.
86	>	*/
87	>	E poll();
88
89		/**
90	<	* Delete and return the element produced by poll, if the queue is
91	<	* not empty.
92	<	* @return an element
93	<	* @throws NoSuchElementException if empty
94	<	**/
95	<	public E remove() throws NoSuchElementException;
90	>	* Remove and return an element from the queue.  This method differs
91	>	* from the <tt>poll</tt> method in that it throws an exception if the
92	>	* queue is empty.
93	>	*
94	>	* @return an element previously on the queue.
95	>	* @throws NoSuchElementException if the queue is empty.
96	>	*/
97	>	E remove() throws NoSuchElementException;
98
99		/**
100	<	* Return but do not delete the element that will be returned by
101	<	* the next call to poll.
102	<	* @return an element, or null if empty
103	<	**/
104	<	public E peek();
100	>	* Return, but do not remove, an element from the queue, or <tt>null</tt>
101	>	* if the queue is empty.  This method returns the same object reference
102	>	* that would be returned by by the <tt>poll</tt> method.  The two methods
103	>	* differ in that this method does not remove the element from the queue.
104	>	*
105	>	* @return an element on the queue, or <tt>null</tt> if the queue is empty.
106	>	*/
107	>	E peek();
108
109		/**
110	<	* Return but do not delete the element that will be returned by
111	<	* the next call to poll, if the queue is not empty.
112	<	* @return an element
113	<	* @throws NoSuchElementException if empty
114	<	**/
115	<	public E element() throws NoSuchElementException;
110	>	* Return, but do not remove, an element from the queue.  This method
111	>	* differs from the <tt>peek</tt> method in that it throws an exception if
112	>	* the queue is empty.
113	>	*
114	>	* @return an element on the queue.
115	>	* @throws NoSuchElementException if the queue is empty.
116	>	*/
117	>	E element() throws NoSuchElementException;
118		}

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines