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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 1.2 by tim, Sun May 18 18:10:02 2003 UTC

#	Line 1 | Line 1
1		package java.util;
2
3		/**
4	<	* Queues are Collections supporting additional basic insertion,
5	<	* extraction, and inspection operations.
6	<	*
7	<	* <p> Queues typically, but do not necessarily order elements in a
8	<	* FIFO (first-in-first-out) manner. Among the exceptions are priority
9	<	* queues, that order elements in accord with supplied
10	<	* Comparators. Every Queue implementation must specify its ordering
11	<	* guarantees,
12	<	*
13	<	* <p> The <tt>offer</tt> method adds an element if possible,
14	<	* otherwise returning <tt>false</tt>. This differs from the
15	<	* Collections.add method, that throws an unchecked exception upon
4	>	* A Collection designed for holding elements prior to processing.
5	>	* Besides basic {@link Collection} operations, queues provide
6	>	* additional insertion, extraction, and inspection operations.
7	>	*
8	>	* <p>Queues typically, but do not necessarily, order elements in a
9	>	* FIFO (first-in-first-out) manner.  Among the exceptions are priority
10	>	* queues, which order elements according to a supplied comparators, or
11	>	* the elements natural ordering.  Every Queue implementation must specify
12	>	* its ordering guarantees.
13	>	*
14	>	* <p>The {@link #offer(E)} method adds an element if possible, otherwise
15	>	* returning <tt>false</tt>.  This differs from the {@link
16	>	* Collections#add(Object)} method, which throws an unchecked exception upon
17		* failure. It is designed for use in collections in which failure to
18		* add is a normal, rather than exceptional occurrence, for example,
19	<	* in fixed-capacity queues.
19	>	* in fixed-capacity (or &ldquo;bounded&rdquo;) queues.
20		*
21	<	* <p> The <tt>remove</tt> and <tt>poll</tt> methods delete and return
22	<	* an element in accord with the implementation's ordering policies --
23	<	* for example, in FIFO queues, it will return the oldest element.
24	<	* The <tt>remove</tt> and <tt>poll</tt> differ only in their behavior
25	<	* when the queue is empty: <tt>poll</tt> returns <tt>null</tt> while
26	<	* <tt>remove</tt> throws an exception. These are designed for usage
26	<	* contexts in which emptiness is considered to be normal versus
27	<	* exceptional.
21	>	* <p>The {@link #remove()} and {@link #poll()} methods remove and return an
22	>	* element in accord with the implementation's ordering policy. For example,
23	>	* in FIFO queues, they remove and return the oldest element in the queue.
24	>	* The <tt>remove()</tt> and <tt>poll()</tt> methods differ only in their
25	>	* behavior when the queue is empty: the <tt>remove()</tt> method throws an
26	>	* exception, while the <tt>poll()</tt> method returns <tt>null</tt>.
27		*
28	<	* <p> The <tt>element</tt> and <tt>peek</tt> methods return but do
28	>	* <p>The {@link #element()} and {@link #peek()} methods return but do
29		* not delete the element that would be obtained by a call to
30	<	* <tt>remove</tt> and <tt>poll</tt> respectively.
30	>	* the <tt>remove</tt> and <tt>poll</tt> methods respectively.
31		*
32	<	* <p> The Queue interface does not define blocking queue methods
33	<	* (i.e., those that wait for elements to appear and/or for space to
34	<	* be available) that are common in concurrent programming. These are
35	<	* defined in the extended java.util.concurrent.BlockingQueue
36	<	* interface.
37	<	*
38	<	* <p> Queue implementations generally do not allow insertion of
39	<	* <tt>null</tt>. Even in those that allow it, it is a very bad idea
40	<	* to do so, since <tt>null</tt> is also used as a sentinel by
41	<	* <tt>poll</tt> to indicate that no elements exist.
42	<	**/
32	>	* <p>The <tt>Queue</tt> interface does not define the <i>blocking queue
33	>	* methods</i>, which are common in concurrent programming.  These methods,
34	>	* which wait for elements to appear or for space to become available, are
35	>	* defined in the {@link java.util.concurrent.BlockingQueue} interface, which
36	>	* extends this interface.
37	>	*
38	>	* <p><tt>Queue</tt> implementations generally do not allow insertion of
39	>	* <tt>null</tt> elements.  Even in the few implementations that permit it,
40	>	* it is a bad idea, as <tt>null</tt> is also used as a special return value
41	>	* by the <tt>poll</tt> method to indicate that the queue contains no
42	>	* elements.
43	>	*
44	>	* <p>This interface is a member of the
45	>	* <a href="{@docRoot}/../guide/collections/index.html">
46	>	* Java Collections Framework</a>.
47	>	*
48	>	* @see Collection
49	>	* @see LinkedList
50	>	* @see PriorityQueue
51	>	* @see LinkedQueue
52	>	* @see java.util.concurrent.BlockingQueue
53	>	* @see java.util.concurrent.ArrayBlockingQueue
54	>	* @see java.util.concurrent.LinkedBlockingQueue
55	>	* @see java.util.concurrent.PriorityBlockingQueue
56	>	*/
57		public interface Queue<E> extends Collection<E> {
45	–
58		/**
59	<	* Add the given object to this queue if possible.
60	<	* @param x the object to add
61	<	* @return true if successful
62	<	**/
63	<	public boolean offer(E x);
59	>	* Add the specified element to this queue, if possible.
60	>	*
61	>	* @param element the element to add.
62	>	* @return true if it was possible to add the element to the queue.
63	>	*/
64	>	public boolean offer(E element);
65
66		/**
67	<	* Delete and return an object from the queue if one is available.
68	<	* @return the object, or null if the queue is empty.
69	<	**/
67	>	* Remove and return an element from the queue if one is available.
68	>	* Exactly which element is removed from the queue is a function
69	>	* of the queue's ordering policy, which differs from implementation
70	>	* to implementation.  Possible orderings include (but are not limited
71	>	* to) first-in-first-out (FIFO), element priority, and arbitrary.
72	>	*
73	>	* @return an element previously on the queue, or <tt>null</tt> if the
74	>	*         queue is empty.
75	>	*/
76		public E poll();
77
78		/**
79	<	* Delete and return the element produced by poll, if the queue is
80	<	* not empty.
81	<	* @return an element
82	<	* @throws NoSuchElementException if empty
83	<	**/
79	>	* Remove and return an element from the queue.  This method differs
80	>	* from the <tt>poll</tt> method in that it throws an exception if the
81	>	* queue is empty.
82	>	*
83	>	* @return an element previously on the queue.
84	>	* @throws NoSuchElementException if the queue is empty.
85	>	*/
86		public E remove() throws NoSuchElementException;
87
88		/**
89	<	* Return but do not delete the element that will be returned by
90	<	* the next call to poll.
91	<	* @return an element, or null if empty
92	<	**/
89	>	* Return, but do not remove, an element from the queue, or <tt>null</tt>
90	>	* if the queue is empty.  This method returns the same object reference
91	>	* 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.
93	>	*
94	>	* @return an element on the queue, or <tt>null</tt> if the queue is empty.
95	>	*/
96		public E peek();
97
98		/**
99	<	* Return but do not delete the element that will be returned by
100	<	* the next call to poll, if the queue is not empty.
101	<	* @return an element
102	<	* @throws NoSuchElementException if empty
103	<	**/
99	>	* Return, but do not remove, an element from the queue.  This method
100	>	* differs from the <tt>peek</tt> method in that it throws an exception if
101	>	* the queue is empty.
102	>	*
103	>	* @return an element on the queue.
104	>	* @throws NoSuchElementException if the queue is empty.
105	>	*/
106		public E element() throws NoSuchElementException;
107		}

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