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><tt>BlockingQueue</tt> 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
 * <tt>null</tt> or <tt>false</tt>, 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>
 *  <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 <tt>BlockingQueue</tt> does not accept <tt>null</tt> elements.
 * Implementations throw <tt>NullPointerException</tt> on attempts
 * to <tt>add</tt>, <tt>put</tt> or <tt>offer</tt> a <tt>null</tt>.  A
 * <tt>null</tt> is used as a sentinel value to indicate failure of
 * <tt>poll</tt> operations.
 *
 * <p>A <tt>BlockingQueue</tt> may be capacity bounded. At any given
 * time it may have a <tt>remainingCapacity</tt> beyond which no
 * additional elements can be <tt>put</tt> without blocking.
 * A <tt>BlockingQueue</tt> without any intrinsic capacity constraints always
 * reports a remaining capacity of <tt>Integer.MAX_VALUE</tt>.
 *
 * <p><tt>BlockingQueue</tt> 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
 * <tt>remove(x)</tt>. 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><tt>BlockingQueue</tt> 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 <tt>addAll</tt>,
 * <tt>containsAll</tt>, <tt>retainAll</tt> and <tt>removeAll</tt> are
 * <em>not</em> necessarily performed atomically unless specified
 * otherwise in an implementation. So it is possible, for example, for
 * <tt>addAll(c)</tt> to fail (throwing an exception) after adding
 * only some of the elements in <tt>c</tt>.
 *
 * <p>A <tt>BlockingQueue</tt> 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 <tt>BlockingQueue</tt> 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
     * <tt>true</tt> upon success and throwing an
     * <tt>IllegalStateException</tt> 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 <tt>true</tt> (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
     * <tt>true</tt> upon success and <tt>false</tt> 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 <tt>true</tt> if the element was added to this queue, else
     *         <tt>false</tt>
     * @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
     *        <tt>unit</tt>
     * @param unit a <tt>TimeUnit</tt> determining how to interpret the
     *        <tt>timeout</tt> parameter
     * @return <tt>true</tt> if successful, or <tt>false</tt> 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
     *        <tt>unit</tt>
     * @param unit a <tt>TimeUnit</tt> determining how to interpret the
     *        <tt>timeout</tt> parameter
     * @return the head of this queue, or <tt>null</tt> 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 <tt>Integer.MAX_VALUE</tt> 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 <tt>remainingCapacity</tt>
     * 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 <tt>e</tt> such
     * that <tt>o.equals(e)</tt>, if this queue contains one or more such
     * elements.
     * Returns <tt>true</tt> 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 <tt>true</tt> 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 <tt>true</tt> if this queue contains the specified element.
     * More formally, returns <tt>true</tt> if and only if this queue contains
     * at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
     *
     * @param o object to be checked for containment in this queue
     * @return <tt>true</tt> 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 <tt>c</tt> 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
     * <tt>IllegalArgumentException</tt>. 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 <tt>c</tt> 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
     * <tt>IllegalArgumentException</tt>. 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:	1.1
Committed:	Sun Dec 16 20:55:15 2012 UTC (11 years, 5 months ago) by dl
Branch:	MAIN
Log Message:	Create src/jdk7 package
#	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			* <p><tt>BlockingQueue</tt> 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			* <tt>null</tt> or <tt>false</tt>, 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			* <tr>
30			* <td></td>
31			* <td ALIGN=CENTER><em>Throws exception</em></td>
32			* <td ALIGN=CENTER><em>Special value</em></td>
33			* <td ALIGN=CENTER><em>Blocks</em></td>
34			* <td ALIGN=CENTER><em>Times out</em></td>
35			* </tr>
36			* <tr>
37			* <td><b>Insert</b></td>
38			* <td>{@link #add add(e)}</td>
39			* <td>{@link #offer offer(e)}</td>
40			* <td>{@link #put put(e)}</td>
41			* <td>{@link #offer(Object, long, TimeUnit) offer(e, time, unit)}</td>
42			* </tr>
43			* <tr>
44			* <td><b>Remove</b></td>
45			* <td>{@link #remove remove()}</td>
46			* <td>{@link #poll poll()}</td>
47			* <td>{@link #take take()}</td>
48			* <td>{@link #poll(long, TimeUnit) poll(time, unit)}</td>
49			* </tr>
50			* <tr>
51			* <td><b>Examine</b></td>
52			* <td>{@link #element element()}</td>
53			* <td>{@link #peek peek()}</td>
54			* <td><em>not applicable</em></td>
55			* <td><em>not applicable</em></td>
56			* </tr>
57			* </table>
58			*
59			* <p>A <tt>BlockingQueue</tt> does not accept <tt>null</tt> elements.
60			* Implementations throw <tt>NullPointerException</tt> on attempts
61			* to <tt>add</tt>, <tt>put</tt> or <tt>offer</tt> a <tt>null</tt>. A
62			* <tt>null</tt> is used as a sentinel value to indicate failure of
63			* <tt>poll</tt> operations.
64			*
65			* <p>A <tt>BlockingQueue</tt> may be capacity bounded. At any given
66			* time it may have a <tt>remainingCapacity</tt> beyond which no
67			* additional elements can be <tt>put</tt> without blocking.
68			* A <tt>BlockingQueue</tt> without any intrinsic capacity constraints always
69			* reports a remaining capacity of <tt>Integer.MAX_VALUE</tt>.
70			*
71			* <p><tt>BlockingQueue</tt> implementations are designed to be used
72			* primarily for producer-consumer queues, but additionally support
73			* the {@link java.util.Collection} interface. So, for example, it is
74			* possible to remove an arbitrary element from a queue using
75			* <tt>remove(x)</tt>. However, such operations are in general
76			* <em>not</em> performed very efficiently, and are intended for only
77			* occasional use, such as when a queued message is cancelled.
78			*
79			* <p><tt>BlockingQueue</tt> implementations are thread-safe. All
80			* queuing methods achieve their effects atomically using internal
81			* locks or other forms of concurrency control. However, the
82			* <em>bulk</em> Collection operations <tt>addAll</tt>,
83			* <tt>containsAll</tt>, <tt>retainAll</tt> and <tt>removeAll</tt> are
84			* <em>not</em> necessarily performed atomically unless specified
85			* otherwise in an implementation. So it is possible, for example, for
86			* <tt>addAll(c)</tt> to fail (throwing an exception) after adding
87			* only some of the elements in <tt>c</tt>.
88			*
89			* <p>A <tt>BlockingQueue</tt> does <em>not</em> intrinsically support
90			* any kind of "close" or "shutdown" operation to
91			* indicate that no more items will be added. The needs and usage of
92			* such features tend to be implementation-dependent. For example, a
93			* common tactic is for producers to insert special
94			* <em>end-of-stream</em> or <em>poison</em> objects, that are
95			* interpreted accordingly when taken by consumers.
96			*
97			* <p>
98			* Usage example, based on a typical producer-consumer scenario.
99			* Note that a <tt>BlockingQueue</tt> can safely be used with multiple
100			* producers and multiple consumers.
101			* <pre> {@code
102			* class Producer implements Runnable {
103			* private final BlockingQueue queue;
104			* Producer(BlockingQueue q) { queue = q; }
105			* public void run() {
106			* try {
107			* while (true) { queue.put(produce()); }
108			* } catch (InterruptedException ex) { ... handle ...}
109			* }
110			* Object produce() { ... }
111			* }
112			*
113			* class Consumer implements Runnable {
114			* private final BlockingQueue queue;
115			* Consumer(BlockingQueue q) { queue = q; }
116			* public void run() {
117			* try {
118			* while (true) { consume(queue.take()); }
119			* } catch (InterruptedException ex) { ... handle ...}
120			* }
121			* void consume(Object x) { ... }
122			* }
123			*
124			* class Setup {
125			* void main() {
126			* BlockingQueue q = new SomeQueueImplementation();
127			* Producer p = new Producer(q);
128			* Consumer c1 = new Consumer(q);
129			* Consumer c2 = new Consumer(q);
130			* new Thread(p).start();
131			* new Thread(c1).start();
132			* new Thread(c2).start();
133			* }
134			* }}</pre>
135			*
136			* <p>Memory consistency effects: As with other concurrent
137			* collections, actions in a thread prior to placing an object into a
138			* {@code BlockingQueue}
139			* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
140			* actions subsequent to the access or removal of that element from
141			* the {@code BlockingQueue} in another thread.
142			*
143			* <p>This interface is a member of the
144			* <a href="{@docRoot}/../technotes/guides/collections/index.html">
145			* Java Collections Framework</a>.
146			*
147			* @since 1.5
148			* @author Doug Lea
149			* @param <E> the type of elements held in this collection
150			*/
151			public interface BlockingQueue<E> extends Queue<E> {
152			/**
153			* Inserts the specified element into this queue if it is possible to do
154			* so immediately without violating capacity restrictions, returning
155			* <tt>true</tt> upon success and throwing an
156			* <tt>IllegalStateException</tt> if no space is currently available.
157			* When using a capacity-restricted queue, it is generally preferable to
158			* use {@link #offer(Object) offer}.
159			*
160			* @param e the element to add
161			* @return <tt>true</tt> (as specified by {@link Collection#add})
162			* @throws IllegalStateException if the element cannot be added at this
163			* time due to capacity restrictions
164			* @throws ClassCastException if the class of the specified element
165			* prevents it from being added to this queue
166			* @throws NullPointerException if the specified element is null
167			* @throws IllegalArgumentException if some property of the specified
168			* element prevents it from being added to this queue
169			*/
170			boolean add(E e);
171
172			/**
173			* Inserts the specified element into this queue if it is possible to do
174			* so immediately without violating capacity restrictions, returning
175			* <tt>true</tt> upon success and <tt>false</tt> if no space is currently
176			* available. When using a capacity-restricted queue, this method is
177			* generally preferable to {@link #add}, which can fail to insert an
178			* element only by throwing an exception.
179			*
180			* @param e the element to add
181			* @return <tt>true</tt> if the element was added to this queue, else
182			* <tt>false</tt>
183			* @throws ClassCastException if the class of the specified element
184			* prevents it from being added to this queue
185			* @throws NullPointerException if the specified element is null
186			* @throws IllegalArgumentException if some property of the specified
187			* element prevents it from being added to this queue
188			*/
189			boolean offer(E e);
190
191			/**
192			* Inserts the specified element into this queue, waiting if necessary
193			* for space to become available.
194			*
195			* @param e the element to add
196			* @throws InterruptedException if interrupted while waiting
197			* @throws ClassCastException if the class of the specified element
198			* prevents it from being added to this queue
199			* @throws NullPointerException if the specified element is null
200			* @throws IllegalArgumentException if some property of the specified
201			* element prevents it from being added to this queue
202			*/
203			void put(E e) throws InterruptedException;
204
205			/**
206			* Inserts the specified element into this queue, waiting up to the
207			* specified wait time if necessary for space to become available.
208			*
209			* @param e the element to add
210			* @param timeout how long to wait before giving up, in units of
211			* <tt>unit</tt>
212			* @param unit a <tt>TimeUnit</tt> determining how to interpret the
213			* <tt>timeout</tt> parameter
214			* @return <tt>true</tt> if successful, or <tt>false</tt> if
215			* the specified waiting time elapses before space is available
216			* @throws InterruptedException if interrupted while waiting
217			* @throws ClassCastException if the class of the specified element
218			* prevents it from being added to this queue
219			* @throws NullPointerException if the specified element is null
220			* @throws IllegalArgumentException if some property of the specified
221			* element prevents it from being added to this queue
222			*/
223			boolean offer(E e, long timeout, TimeUnit unit)
224			throws InterruptedException;
225
226			/**
227			* Retrieves and removes the head of this queue, waiting if necessary
228			* until an element becomes available.
229			*
230			* @return the head of this queue
231			* @throws InterruptedException if interrupted while waiting
232			*/
233			E take() throws InterruptedException;
234
235			/**
236			* Retrieves and removes the head of this queue, waiting up to the
237			* specified wait time if necessary for an element to become available.
238			*
239			* @param timeout how long to wait before giving up, in units of
240			* <tt>unit</tt>
241			* @param unit a <tt>TimeUnit</tt> determining how to interpret the
242			* <tt>timeout</tt> parameter
243			* @return the head of this queue, or <tt>null</tt> if the
244			* specified waiting time elapses before an element is available
245			* @throws InterruptedException if interrupted while waiting
246			*/
247			E poll(long timeout, TimeUnit unit)
248			throws InterruptedException;
249
250			/**
251			* Returns the number of additional elements that this queue can ideally
252			* (in the absence of memory or resource constraints) accept without
253			* blocking, or <tt>Integer.MAX_VALUE</tt> if there is no intrinsic
254			* limit.
255			*
256			* <p>Note that you <em>cannot</em> always tell if an attempt to insert
257			* an element will succeed by inspecting <tt>remainingCapacity</tt>
258			* because it may be the case that another thread is about to
259			* insert or remove an element.
260			*
261			* @return the remaining capacity
262			*/
263			int remainingCapacity();
264
265			/**
266			* Removes a single instance of the specified element from this queue,
267			* if it is present. More formally, removes an element <tt>e</tt> such
268			* that <tt>o.equals(e)</tt>, if this queue contains one or more such
269			* elements.
270			* Returns <tt>true</tt> if this queue contained the specified element
271			* (or equivalently, if this queue changed as a result of the call).
272			*
273			* @param o element to be removed from this queue, if present
274			* @return <tt>true</tt> if this queue changed as a result of the call
275			* @throws ClassCastException if the class of the specified element
276			* is incompatible with this queue
277			* (<a href="../Collection.html#optional-restrictions">optional</a>)
278			* @throws NullPointerException if the specified element is null
279			* (<a href="../Collection.html#optional-restrictions">optional</a>)
280			*/
281			boolean remove(Object o);
282
283			/**
284			* Returns <tt>true</tt> if this queue contains the specified element.
285			* More formally, returns <tt>true</tt> if and only if this queue contains
286			* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
287			*
288			* @param o object to be checked for containment in this queue
289			* @return <tt>true</tt> if this queue contains the specified element
290			* @throws ClassCastException if the class of the specified element
291			* is incompatible with this queue
292			* (<a href="../Collection.html#optional-restrictions">optional</a>)
293			* @throws NullPointerException if the specified element is null
294			* (<a href="../Collection.html#optional-restrictions">optional</a>)
295			*/
296			public boolean contains(Object o);
297
298			/**
299			* Removes all available elements from this queue and adds them
300			* to the given collection. This operation may be more
301			* efficient than repeatedly polling this queue. A failure
302			* encountered while attempting to add elements to
303			* collection <tt>c</tt> may result in elements being in neither,
304			* either or both collections when the associated exception is
305			* thrown. Attempts to drain a queue to itself result in
306			* <tt>IllegalArgumentException</tt>. Further, the behavior of
307			* this operation is undefined if the specified collection is
308			* modified while the operation is in progress.
309			*
310			* @param c the collection to transfer elements into
311			* @return the number of elements transferred
312			* @throws UnsupportedOperationException if addition of elements
313			* is not supported by the specified collection
314			* @throws ClassCastException if the class of an element of this queue
315			* prevents it from being added to the specified collection
316			* @throws NullPointerException if the specified collection is null
317			* @throws IllegalArgumentException if the specified collection is this
318			* queue, or some property of an element of this queue prevents
319			* it from being added to the specified collection
320			*/
321			int drainTo(Collection<? super E> c);
322
323			/**
324			* Removes at most the given number of available elements from
325			* this queue and adds them to the given collection. A failure
326			* encountered while attempting to add elements to
327			* collection <tt>c</tt> may result in elements being in neither,
328			* either or both collections when the associated exception is
329			* thrown. Attempts to drain a queue to itself result in
330			* <tt>IllegalArgumentException</tt>. Further, the behavior of
331			* this operation is undefined if the specified collection is
332			* modified while the operation is in progress.
333			*
334			* @param c the collection to transfer elements into
335			* @param maxElements the maximum number of elements to transfer
336			* @return the number of elements transferred
337			* @throws UnsupportedOperationException if addition of elements
338			* is not supported by the specified collection
339			* @throws ClassCastException if the class of an element of this queue
340			* prevents it from being added to the specified collection
341			* @throws NullPointerException if the specified collection is null
342			* @throws IllegalArgumentException if the specified collection is this
343			* queue, or some property of an element of this queue prevents
344			* it from being added to the specified collection
345			*/
346			int drainTo(Collection<? super E> c, int maxElements);
347			}