util/concurrent/BlockingQueue.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

package java.util.concurrent;

import java.util.Collection;
import java.util.Queue;

/**
 * A {@link java.util.Queue} that additionally supports operations
 * that wait for the queue to become non-empty when retrieving an
 * element, and wait for space to become available in the queue when
 * storing an element.
 *
 * <p>{@code BlockingQueue} methods come in four forms, with different ways
 * of handling operations that cannot be satisfied immediately, but may be
 * satisfied at some point in the future:
 * one throws an exception, the second returns a special value (either
 * {@code null} or {@code false}, depending on the operation), the third
 * blocks the current thread indefinitely until the operation can succeed,
 * and the fourth blocks for only a given maximum time limit before giving
 * up.  These methods are summarized in the following table:
 *
 * <p>
 * <table BORDER CELLPADDING=3 CELLSPACING=1>
 * <caption>Summary of BlockingQueue methods</caption>
 *  <tr>
 *    <td></td>
 *    <td ALIGN=CENTER><em>Throws exception</em></td>
 *    <td ALIGN=CENTER><em>Special value</em></td>
 *    <td ALIGN=CENTER><em>Blocks</em></td>
 *    <td ALIGN=CENTER><em>Times out</em></td>
 *  </tr>
 *  <tr>
 *    <td><b>Insert</b></td>
 *    <td>{@link #add add(e)}</td>
 *    <td>{@link #offer offer(e)}</td>
 *    <td>{@link #put put(e)}</td>
 *    <td>{@link #offer(Object, long, TimeUnit) offer(e, time, unit)}</td>
 *  </tr>
 *  <tr>
 *    <td><b>Remove</b></td>
 *    <td>{@link #remove remove()}</td>
 *    <td>{@link #poll poll()}</td>
 *    <td>{@link #take take()}</td>
 *    <td>{@link #poll(long, TimeUnit) poll(time, unit)}</td>
 *  </tr>
 *  <tr>
 *    <td><b>Examine</b></td>
 *    <td>{@link #element element()}</td>
 *    <td>{@link #peek peek()}</td>
 *    <td><em>not applicable</em></td>
 *    <td><em>not applicable</em></td>
 *  </tr>
 * </table>
 *
 * <p>A {@code BlockingQueue} does not accept {@code null} elements.
 * Implementations throw {@code NullPointerException} on attempts
 * to {@code add}, {@code put} or {@code offer} a {@code null}.  A
 * {@code null} is used as a sentinel value to indicate failure of
 * {@code poll} operations.
 *
 * <p>A {@code BlockingQueue} may be capacity bounded. At any given
 * time it may have a {@code remainingCapacity} beyond which no
 * additional elements can be {@code put} without blocking.
 * A {@code BlockingQueue} without any intrinsic capacity constraints always
 * reports a remaining capacity of {@code Integer.MAX_VALUE}.
 *
 * <p>{@code BlockingQueue} implementations are designed to be used
 * primarily for producer-consumer queues, but additionally support
 * the {@link java.util.Collection} interface.  So, for example, it is
 * possible to remove an arbitrary element from a queue using
 * {@code remove(x)}. However, such operations are in general
 * <em>not</em> performed very efficiently, and are intended for only
 * occasional use, such as when a queued message is cancelled.
 *
 * <p>{@code BlockingQueue} implementations are thread-safe.  All
 * queuing methods achieve their effects atomically using internal
 * locks or other forms of concurrency control. However, the
 * <em>bulk</em> Collection operations {@code addAll},
 * {@code containsAll}, {@code retainAll} and {@code removeAll} are
 * <em>not</em> necessarily performed atomically unless specified
 * otherwise in an implementation. So it is possible, for example, for
 * {@code addAll(c)} to fail (throwing an exception) after adding
 * only some of the elements in {@code c}.
 *
 * <p>A {@code BlockingQueue} does <em>not</em> intrinsically support
 * any kind of &quot;close&quot; or &quot;shutdown&quot; operation to
 * indicate that no more items will be added.  The needs and usage of
 * such features tend to be implementation-dependent. For example, a
 * common tactic is for producers to insert special
 * <em>end-of-stream</em> or <em>poison</em> objects, that are
 * interpreted accordingly when taken by consumers.
 *
 * <p>
 * Usage example, based on a typical producer-consumer scenario.
 * Note that a {@code BlockingQueue} can safely be used with multiple
 * producers and multiple consumers.
 *  <pre> {@code
 * class Producer implements Runnable {
 *   private final BlockingQueue queue;
 *   Producer(BlockingQueue q) { queue = q; }
 *   public void run() {
 *     try {
 *       while (true) { queue.put(produce()); }
 *     } catch (InterruptedException ex) { ... handle ...}
 *   }
 *   Object produce() { ... }
 * }
 *
 * class Consumer implements Runnable {
 *   private final BlockingQueue queue;
 *   Consumer(BlockingQueue q) { queue = q; }
 *   public void run() {
 *     try {
 *       while (true) { consume(queue.take()); }
 *     } catch (InterruptedException ex) { ... handle ...}
 *   }
 *   void consume(Object x) { ... }
 * }
 *
 * class Setup {
 *   void main() {
 *     BlockingQueue q = new SomeQueueImplementation();
 *     Producer p = new Producer(q);
 *     Consumer c1 = new Consumer(q);
 *     Consumer c2 = new Consumer(q);
 *     new Thread(p).start();
 *     new Thread(c1).start();
 *     new Thread(c2).start();
 *   }
 * }}</pre>
 *
 * <p>Memory consistency effects: As with other concurrent
 * collections, actions in a thread prior to placing an object into a
 * {@code BlockingQueue}
 * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
 * actions subsequent to the access or removal of that element from
 * the {@code BlockingQueue} in another thread.
 *
 * <p>This interface is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @since 1.5
 * @author Doug Lea
 * @param <E> the type of elements held in this collection
 */
public interface BlockingQueue<E> extends Queue<E> {
    /**
     * Inserts the specified element into this queue if it is possible to do
     * so immediately without violating capacity restrictions, returning
     * {@code true} upon success and throwing an
     * {@code IllegalStateException} if no space is currently available.
     * When using a capacity-restricted queue, it is generally preferable to
     * use {@link #offer(Object) offer}.
     *
     * @param e the element to add
     * @return {@code true} (as specified by {@link Collection#add})
     * @throws IllegalStateException if the element cannot be added at this
     *         time due to capacity restrictions
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this queue
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException if some property of the specified
     *         element prevents it from being added to this queue
     */
    boolean add(E e);

    /**
     * Inserts the specified element into this queue if it is possible to do
     * so immediately without violating capacity restrictions, returning
     * {@code true} upon success and {@code false} if no space is currently
     * available.  When using a capacity-restricted queue, this method is
     * generally preferable to {@link #add}, which can fail to insert an
     * element only by throwing an exception.
     *
     * @param e the element to add
     * @return {@code true} if the element was added to this queue, else
     *         {@code false}
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this queue
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException if some property of the specified
     *         element prevents it from being added to this queue
     */
    boolean offer(E e);

    /**
     * Inserts the specified element into this queue, waiting if necessary
     * for space to become available.
     *
     * @param e the element to add
     * @throws InterruptedException if interrupted while waiting
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this queue
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException if some property of the specified
     *         element prevents it from being added to this queue
     */
    void put(E e) throws InterruptedException;

    /**
     * Inserts the specified element into this queue, waiting up to the
     * specified wait time if necessary for space to become available.
     *
     * @param e the element to add
     * @param timeout how long to wait before giving up, in units of
     *        {@code unit}
     * @param unit a {@code TimeUnit} determining how to interpret the
     *        {@code timeout} parameter
     * @return {@code true} if successful, or {@code false} if
     *         the specified waiting time elapses before space is available
     * @throws InterruptedException if interrupted while waiting
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this queue
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException if some property of the specified
     *         element prevents it from being added to this queue
     */
    boolean offer(E e, long timeout, TimeUnit unit)
        throws InterruptedException;

    /**
     * Retrieves and removes the head of this queue, waiting if necessary
     * until an element becomes available.
     *
     * @return the head of this queue
     * @throws InterruptedException if interrupted while waiting
     */
    E take() throws InterruptedException;

    /**
     * Retrieves and removes the head of this queue, waiting up to the
     * specified wait time if necessary for an element to become available.
     *
     * @param timeout how long to wait before giving up, in units of
     *        {@code unit}
     * @param unit a {@code TimeUnit} determining how to interpret the
     *        {@code timeout} parameter
     * @return the head of this queue, or {@code null} if the
     *         specified waiting time elapses before an element is available
     * @throws InterruptedException if interrupted while waiting
     */
    E poll(long timeout, TimeUnit unit)
        throws InterruptedException;

    /**
     * Returns the number of additional elements that this queue can ideally
     * (in the absence of memory or resource constraints) accept without
     * blocking, or {@code Integer.MAX_VALUE} if there is no intrinsic
     * limit.
     *
     * <p>Note that you <em>cannot</em> always tell if an attempt to insert
     * an element will succeed by inspecting {@code remainingCapacity}
     * because it may be the case that another thread is about to
     * insert or remove an element.
     *
     * @return the remaining capacity
     */
    int remainingCapacity();

    /**
     * Removes a single instance of the specified element from this queue,
     * if it is present.  More formally, removes an element {@code e} such
     * that {@code o.equals(e)}, if this queue contains one or more such
     * elements.
     * Returns {@code true} if this queue contained the specified element
     * (or equivalently, if this queue changed as a result of the call).
     *
     * @param o element to be removed from this queue, if present
     * @return {@code true} if this queue changed as a result of the call
     * @throws ClassCastException if the class of the specified element
     *         is incompatible with this queue
     *         (<a href="../Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if the specified element is null
     *         (<a href="../Collection.html#optional-restrictions">optional</a>)
     */
    boolean remove(Object o);

    /**
     * Returns {@code true} if this queue contains the specified element.
     * More formally, returns {@code true} if and only if this queue contains
     * at least one element {@code e} such that {@code o.equals(e)}.
     *
     * @param o object to be checked for containment in this queue
     * @return {@code true} if this queue contains the specified element
     * @throws ClassCastException if the class of the specified element
     *         is incompatible with this queue
     *         (<a href="../Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if the specified element is null
     *         (<a href="../Collection.html#optional-restrictions">optional</a>)
     */
    public boolean contains(Object o);

    /**
     * Removes all available elements from this queue and adds them
     * to the given collection.  This operation may be more
     * efficient than repeatedly polling this queue.  A failure
     * encountered while attempting to add elements to
     * collection {@code c} may result in elements being in neither,
     * either or both collections when the associated exception is
     * thrown.  Attempts to drain a queue to itself result in
     * {@code IllegalArgumentException}. Further, the behavior of
     * this operation is undefined if the specified collection is
     * modified while the operation is in progress.
     *
     * @param c the collection to transfer elements into
     * @return the number of elements transferred
     * @throws UnsupportedOperationException if addition of elements
     *         is not supported by the specified collection
     * @throws ClassCastException if the class of an element of this queue
     *         prevents it from being added to the specified collection
     * @throws NullPointerException if the specified collection is null
     * @throws IllegalArgumentException if the specified collection is this
     *         queue, or some property of an element of this queue prevents
     *         it from being added to the specified collection
     */
    int drainTo(Collection<? super E> c);

    /**
     * Removes at most the given number of available elements from
     * this queue and adds them to the given collection.  A failure
     * encountered while attempting to add elements to
     * collection {@code c} may result in elements being in neither,
     * either or both collections when the associated exception is
     * thrown.  Attempts to drain a queue to itself result in
     * {@code IllegalArgumentException}. Further, the behavior of
     * this operation is undefined if the specified collection is
     * modified while the operation is in progress.
     *
     * @param c the collection to transfer elements into
     * @param maxElements the maximum number of elements to transfer
     * @return the number of elements transferred
     * @throws UnsupportedOperationException if addition of elements
     *         is not supported by the specified collection
     * @throws ClassCastException if the class of an element of this queue
     *         prevents it from being added to the specified collection
     * @throws NullPointerException if the specified collection is null
     * @throws IllegalArgumentException if the specified collection is this
     *         queue, or some property of an element of this queue prevents
     *         it from being added to the specified collection
     */
    int drainTo(Collection<? super E> c, int maxElements);
}
Revision:	1.3
Committed:	Sat Jul 20 19:49:43 2013 UTC (10 years, 10 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.2:	+1 -0 lines
Log Message:	sync javadoc fixes from src/main
#	User	Rev	Content
1	dl	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.concurrent;
8
9			import java.util.Collection;
10			import java.util.Queue;
11
12			/**
13			* A {@link java.util.Queue} that additionally supports operations
14			* that wait for the queue to become non-empty when retrieving an
15			* element, and wait for space to become available in the queue when
16			* storing an element.
17			*
18	jsr166	1.2	* <p>{@code BlockingQueue} methods come in four forms, with different ways
19	dl	1.1	* of handling operations that cannot be satisfied immediately, but may be
20			* satisfied at some point in the future:
21			* one throws an exception, the second returns a special value (either
22	jsr166	1.2	* {@code null} or {@code false}, depending on the operation), the third
23	dl	1.1	* blocks the current thread indefinitely until the operation can succeed,
24			* and the fourth blocks for only a given maximum time limit before giving
25			* up. These methods are summarized in the following table:
26			*
27			* <p>
28			* <table BORDER CELLPADDING=3 CELLSPACING=1>
29	jsr166	1.3	* <caption>Summary of BlockingQueue methods</caption>
30	dl	1.1	* <tr>
31			* <td></td>
32			* <td ALIGN=CENTER><em>Throws exception</em></td>
33			* <td ALIGN=CENTER><em>Special value</em></td>
34			* <td ALIGN=CENTER><em>Blocks</em></td>
35			* <td ALIGN=CENTER><em>Times out</em></td>
36			* </tr>
37			* <tr>
38			* <td><b>Insert</b></td>
39			* <td>{@link #add add(e)}</td>
40			* <td>{@link #offer offer(e)}</td>
41			* <td>{@link #put put(e)}</td>
42			* <td>{@link #offer(Object, long, TimeUnit) offer(e, time, unit)}</td>
43			* </tr>
44			* <tr>
45			* <td><b>Remove</b></td>
46			* <td>{@link #remove remove()}</td>
47			* <td>{@link #poll poll()}</td>
48			* <td>{@link #take take()}</td>
49			* <td>{@link #poll(long, TimeUnit) poll(time, unit)}</td>
50			* </tr>
51			* <tr>
52			* <td><b>Examine</b></td>
53			* <td>{@link #element element()}</td>
54			* <td>{@link #peek peek()}</td>
55			* <td><em>not applicable</em></td>
56			* <td><em>not applicable</em></td>
57			* </tr>
58			* </table>
59			*
60	jsr166	1.2	* <p>A {@code BlockingQueue} does not accept {@code null} elements.
61			* Implementations throw {@code NullPointerException} on attempts
62			* to {@code add}, {@code put} or {@code offer} a {@code null}. A
63			* {@code null} is used as a sentinel value to indicate failure of
64			* {@code poll} operations.
65			*
66			* <p>A {@code BlockingQueue} may be capacity bounded. At any given
67			* time it may have a {@code remainingCapacity} beyond which no
68			* additional elements can be {@code put} without blocking.
69			* A {@code BlockingQueue} without any intrinsic capacity constraints always
70			* reports a remaining capacity of {@code Integer.MAX_VALUE}.
71	dl	1.1	*
72	jsr166	1.2	* <p>{@code BlockingQueue} implementations are designed to be used
73	dl	1.1	* primarily for producer-consumer queues, but additionally support
74			* the {@link java.util.Collection} interface. So, for example, it is
75			* possible to remove an arbitrary element from a queue using
76	jsr166	1.2	* {@code remove(x)}. However, such operations are in general
77	dl	1.1	* <em>not</em> performed very efficiently, and are intended for only
78			* occasional use, such as when a queued message is cancelled.
79			*
80	jsr166	1.2	* <p>{@code BlockingQueue} implementations are thread-safe. All
81	dl	1.1	* queuing methods achieve their effects atomically using internal
82			* locks or other forms of concurrency control. However, the
83	jsr166	1.2	* <em>bulk</em> Collection operations {@code addAll},
84			* {@code containsAll}, {@code retainAll} and {@code removeAll} are
85	dl	1.1	* <em>not</em> necessarily performed atomically unless specified
86			* otherwise in an implementation. So it is possible, for example, for
87	jsr166	1.2	* {@code addAll(c)} to fail (throwing an exception) after adding
88			* only some of the elements in {@code c}.
89	dl	1.1	*
90	jsr166	1.2	* <p>A {@code BlockingQueue} does <em>not</em> intrinsically support
91	dl	1.1	* any kind of "close" or "shutdown" operation to
92			* indicate that no more items will be added. The needs and usage of
93			* such features tend to be implementation-dependent. For example, a
94			* common tactic is for producers to insert special
95			* <em>end-of-stream</em> or <em>poison</em> objects, that are
96			* interpreted accordingly when taken by consumers.
97			*
98			* <p>
99			* Usage example, based on a typical producer-consumer scenario.
100	jsr166	1.2	* Note that a {@code BlockingQueue} can safely be used with multiple
101	dl	1.1	* producers and multiple consumers.
102			* <pre> {@code
103			* class Producer implements Runnable {
104			* private final BlockingQueue queue;
105			* Producer(BlockingQueue q) { queue = q; }
106			* public void run() {
107			* try {
108			* while (true) { queue.put(produce()); }
109			* } catch (InterruptedException ex) { ... handle ...}
110			* }
111			* Object produce() { ... }
112			* }
113			*
114			* class Consumer implements Runnable {
115			* private final BlockingQueue queue;
116			* Consumer(BlockingQueue q) { queue = q; }
117			* public void run() {
118			* try {
119			* while (true) { consume(queue.take()); }
120			* } catch (InterruptedException ex) { ... handle ...}
121			* }
122			* void consume(Object x) { ... }
123			* }
124			*
125			* class Setup {
126			* void main() {
127			* BlockingQueue q = new SomeQueueImplementation();
128			* Producer p = new Producer(q);
129			* Consumer c1 = new Consumer(q);
130			* Consumer c2 = new Consumer(q);
131			* new Thread(p).start();
132			* new Thread(c1).start();
133			* new Thread(c2).start();
134			* }
135			* }}</pre>
136			*
137			* <p>Memory consistency effects: As with other concurrent
138			* collections, actions in a thread prior to placing an object into a
139			* {@code BlockingQueue}
140			* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
141			* actions subsequent to the access or removal of that element from
142			* the {@code BlockingQueue} in another thread.
143			*
144			* <p>This interface is a member of the
145			* <a href="{@docRoot}/../technotes/guides/collections/index.html">
146			* Java Collections Framework</a>.
147			*
148			* @since 1.5
149			* @author Doug Lea
150			* @param <E> the type of elements held in this collection
151			*/
152			public interface BlockingQueue<E> extends Queue<E> {
153			/**
154			* Inserts the specified element into this queue if it is possible to do
155			* so immediately without violating capacity restrictions, returning
156	jsr166	1.2	* {@code true} upon success and throwing an
157			* {@code IllegalStateException} if no space is currently available.
158	dl	1.1	* When using a capacity-restricted queue, it is generally preferable to
159			* use {@link #offer(Object) offer}.
160			*
161			* @param e the element to add
162	jsr166	1.2	* @return {@code true} (as specified by {@link Collection#add})
163	dl	1.1	* @throws IllegalStateException if the element cannot be added at this
164			* time due to capacity restrictions
165			* @throws ClassCastException if the class of the specified element
166			* prevents it from being added to this queue
167			* @throws NullPointerException if the specified element is null
168			* @throws IllegalArgumentException if some property of the specified
169			* element prevents it from being added to this queue
170			*/
171			boolean add(E e);
172
173			/**
174			* Inserts the specified element into this queue if it is possible to do
175			* so immediately without violating capacity restrictions, returning
176	jsr166	1.2	* {@code true} upon success and {@code false} if no space is currently
177	dl	1.1	* available. When using a capacity-restricted queue, this method is
178			* generally preferable to {@link #add}, which can fail to insert an
179			* element only by throwing an exception.
180			*
181			* @param e the element to add
182	jsr166	1.2	* @return {@code true} if the element was added to this queue, else
183			* {@code false}
184	dl	1.1	* @throws ClassCastException if the class of the specified element
185			* prevents it from being added to this queue
186			* @throws NullPointerException if the specified element is null
187			* @throws IllegalArgumentException if some property of the specified
188			* element prevents it from being added to this queue
189			*/
190			boolean offer(E e);
191
192			/**
193			* Inserts the specified element into this queue, waiting if necessary
194			* for space to become available.
195			*
196			* @param e the element to add
197			* @throws InterruptedException if interrupted while waiting
198			* @throws ClassCastException if the class of the specified element
199			* prevents it from being added to this queue
200			* @throws NullPointerException if the specified element is null
201			* @throws IllegalArgumentException if some property of the specified
202			* element prevents it from being added to this queue
203			*/
204			void put(E e) throws InterruptedException;
205
206			/**
207			* Inserts the specified element into this queue, waiting up to the
208			* specified wait time if necessary for space to become available.
209			*
210			* @param e the element to add
211			* @param timeout how long to wait before giving up, in units of
212	jsr166	1.2	* {@code unit}
213			* @param unit a {@code TimeUnit} determining how to interpret the
214			* {@code timeout} parameter
215			* @return {@code true} if successful, or {@code false} if
216	dl	1.1	* the specified waiting time elapses before space is available
217			* @throws InterruptedException if interrupted while waiting
218			* @throws ClassCastException if the class of the specified element
219			* prevents it from being added to this queue
220			* @throws NullPointerException if the specified element is null
221			* @throws IllegalArgumentException if some property of the specified
222			* element prevents it from being added to this queue
223			*/
224			boolean offer(E e, long timeout, TimeUnit unit)
225			throws InterruptedException;
226
227			/**
228			* Retrieves and removes the head of this queue, waiting if necessary
229			* until an element becomes available.
230			*
231			* @return the head of this queue
232			* @throws InterruptedException if interrupted while waiting
233			*/
234			E take() throws InterruptedException;
235
236			/**
237			* Retrieves and removes the head of this queue, waiting up to the
238			* specified wait time if necessary for an element to become available.
239			*
240			* @param timeout how long to wait before giving up, in units of
241	jsr166	1.2	* {@code unit}
242			* @param unit a {@code TimeUnit} determining how to interpret the
243			* {@code timeout} parameter
244			* @return the head of this queue, or {@code null} if the
245	dl	1.1	* specified waiting time elapses before an element is available
246			* @throws InterruptedException if interrupted while waiting
247			*/
248			E poll(long timeout, TimeUnit unit)
249			throws InterruptedException;
250
251			/**
252			* Returns the number of additional elements that this queue can ideally
253			* (in the absence of memory or resource constraints) accept without
254	jsr166	1.2	* blocking, or {@code Integer.MAX_VALUE} if there is no intrinsic
255	dl	1.1	* limit.
256			*
257			* <p>Note that you <em>cannot</em> always tell if an attempt to insert
258	jsr166	1.2	* an element will succeed by inspecting {@code remainingCapacity}
259	dl	1.1	* because it may be the case that another thread is about to
260			* insert or remove an element.
261			*
262			* @return the remaining capacity
263			*/
264			int remainingCapacity();
265
266			/**
267			* Removes a single instance of the specified element from this queue,
268	jsr166	1.2	* if it is present. More formally, removes an element {@code e} such
269			* that {@code o.equals(e)}, if this queue contains one or more such
270	dl	1.1	* elements.
271	jsr166	1.2	* Returns {@code true} if this queue contained the specified element
272	dl	1.1	* (or equivalently, if this queue changed as a result of the call).
273			*
274			* @param o element to be removed from this queue, if present
275	jsr166	1.2	* @return {@code true} if this queue changed as a result of the call
276	dl	1.1	* @throws ClassCastException if the class of the specified element
277			* is incompatible with this queue
278			* (<a href="../Collection.html#optional-restrictions">optional</a>)
279			* @throws NullPointerException if the specified element is null
280			* (<a href="../Collection.html#optional-restrictions">optional</a>)
281			*/
282			boolean remove(Object o);
283
284			/**
285	jsr166	1.2	* Returns {@code true} if this queue contains the specified element.
286			* More formally, returns {@code true} if and only if this queue contains
287			* at least one element {@code e} such that {@code o.equals(e)}.
288	dl	1.1	*
289			* @param o object to be checked for containment in this queue
290	jsr166	1.2	* @return {@code true} if this queue contains the specified element
291	dl	1.1	* @throws ClassCastException if the class of the specified element
292			* is incompatible with this queue
293			* (<a href="../Collection.html#optional-restrictions">optional</a>)
294			* @throws NullPointerException if the specified element is null
295			* (<a href="../Collection.html#optional-restrictions">optional</a>)
296			*/
297			public boolean contains(Object o);
298
299			/**
300			* Removes all available elements from this queue and adds them
301			* to the given collection. This operation may be more
302			* efficient than repeatedly polling this queue. A failure
303			* encountered while attempting to add elements to
304	jsr166	1.2	* collection {@code c} may result in elements being in neither,
305	dl	1.1	* either or both collections when the associated exception is
306			* thrown. Attempts to drain a queue to itself result in
307	jsr166	1.2	* {@code IllegalArgumentException}. Further, the behavior of
308	dl	1.1	* this operation is undefined if the specified collection is
309			* modified while the operation is in progress.
310			*
311			* @param c the collection to transfer elements into
312			* @return the number of elements transferred
313			* @throws UnsupportedOperationException if addition of elements
314			* is not supported by the specified collection
315			* @throws ClassCastException if the class of an element of this queue
316			* prevents it from being added to the specified collection
317			* @throws NullPointerException if the specified collection is null
318			* @throws IllegalArgumentException if the specified collection is this
319			* queue, or some property of an element of this queue prevents
320			* it from being added to the specified collection
321			*/
322			int drainTo(Collection<? super E> c);
323
324			/**
325			* Removes at most the given number of available elements from
326			* this queue and adds them to the given collection. A failure
327			* encountered while attempting to add elements to
328	jsr166	1.2	* collection {@code c} may result in elements being in neither,
329	dl	1.1	* either or both collections when the associated exception is
330			* thrown. Attempts to drain a queue to itself result in
331	jsr166	1.2	* {@code IllegalArgumentException}. Further, the behavior of
332	dl	1.1	* this operation is undefined if the specified collection is
333			* modified while the operation is in progress.
334			*
335			* @param c the collection to transfer elements into
336			* @param maxElements the maximum number of elements to transfer
337			* @return the number of elements transferred
338			* @throws UnsupportedOperationException if addition of elements
339			* is not supported by the specified collection
340			* @throws ClassCastException if the class of an element of this queue
341			* prevents it from being added to the specified collection
342			* @throws NullPointerException if the specified collection is null
343			* @throws IllegalArgumentException if the specified collection is this
344			* queue, or some property of an element of this queue prevents
345			* it from being added to the specified collection
346			*/
347			int drainTo(Collection<? super E> c, int maxElements);
348			}