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, 9 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.2:	+1 -0 lines
Log Message:	sync javadoc fixes from src/main
#	Content
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	* <p>{@code BlockingQueue} methods come in four forms, with different ways
19	* 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	* {@code null} or {@code false}, depending on the operation), the third
23	* 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	* <caption>Summary of BlockingQueue methods</caption>
30	* <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	* <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	*
72	* <p>{@code BlockingQueue} implementations are designed to be used
73	* 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	* {@code remove(x)}. However, such operations are in general
77	* <em>not</em> performed very efficiently, and are intended for only
78	* occasional use, such as when a queued message is cancelled.
79	*
80	* <p>{@code BlockingQueue} implementations are thread-safe. All
81	* queuing methods achieve their effects atomically using internal
82	* locks or other forms of concurrency control. However, the
83	* <em>bulk</em> Collection operations {@code addAll},
84	* {@code containsAll}, {@code retainAll} and {@code removeAll} are
85	* <em>not</em> necessarily performed atomically unless specified
86	* otherwise in an implementation. So it is possible, for example, for
87	* {@code addAll(c)} to fail (throwing an exception) after adding
88	* only some of the elements in {@code c}.
89	*
90	* <p>A {@code BlockingQueue} does <em>not</em> intrinsically support
91	* 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	* Note that a {@code BlockingQueue} can safely be used with multiple
101	* 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	* {@code true} upon success and throwing an
157	* {@code IllegalStateException} if no space is currently available.
158	* 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	* @return {@code true} (as specified by {@link Collection#add})
163	* @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	* {@code true} upon success and {@code false} if no space is currently
177	* 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	* @return {@code true} if the element was added to this queue, else
183	* {@code false}
184	* @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	* {@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	* 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	* {@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	* 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	* blocking, or {@code Integer.MAX_VALUE} if there is no intrinsic
255	* limit.
256	*
257	* <p>Note that you <em>cannot</em> always tell if an attempt to insert
258	* an element will succeed by inspecting {@code remainingCapacity}
259	* 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	* 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	* elements.
271	* Returns {@code true} if this queue contained the specified element
272	* (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	* @return {@code true} if this queue changed as a result of the call
276	* @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	* 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	*
289	* @param o object to be checked for containment in this queue
290	* @return {@code true} if this queue contains the specified element
291	* @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	* collection {@code c} may result in elements being in neither,
305	* either or both collections when the associated exception is
306	* thrown. Attempts to drain a queue to itself result in
307	* {@code IllegalArgumentException}. Further, the behavior of
308	* 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	* collection {@code c} may result in elements being in neither,
329	* either or both collections when the associated exception is
330	* thrown. Attempts to drain a queue to itself result in
331	* {@code IllegalArgumentException}. Further, the behavior of
332	* 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	}