LinkedBlockingQueue (Java Platform SE 6) (original) (raw)

java.util.concurrent

Class LinkedBlockingQueue

java.lang.Object extended by java.util.AbstractCollection java.util.AbstractQueue java.util.concurrent.LinkedBlockingQueue

Type Parameters:

E - the type of elements held in this collection

All Implemented Interfaces:

Serializable, Iterable, Collection, BlockingQueue, Queue

public class LinkedBlockingQueue

extends AbstractQueue

implements BlockingQueue, Serializable

An optionally-bounded blocking queue based on linked nodes. This queue orders elements FIFO (first-in-first-out). The head of the queue is that element that has been on the queue the longest time. The tail of the queue is that element that has been on the queue the shortest time. New elements are inserted at the tail of the queue, and the queue retrieval operations obtain elements at the head of the queue. Linked queues typically have higher throughput than array-based queues but less predictable performance in most concurrent applications.

The optional capacity bound constructor argument serves as a way to prevent excessive queue expansion. The capacity, if unspecified, is equal to Integer.MAX_VALUE. Linked nodes are dynamically created upon each insertion unless this would bring the queue above capacity.

This class and its iterator implement all of the_optional_ methods of the Collection and Iterator interfaces.

This class is a member of the Java Collections Framework.

Since:

1.5

See Also:

Serialized Form

Constructor Summary
LinkedBlockingQueue() Creates a LinkedBlockingQueue with a capacity ofInteger.MAX_VALUE.
LinkedBlockingQueue(Collection<? extends E> c) Creates a LinkedBlockingQueue with a capacity ofInteger.MAX_VALUE, initially containing the elements of the given collection, added in traversal order of the collection's iterator.
LinkedBlockingQueue(int capacity) Creates a LinkedBlockingQueue with the given (fixed) capacity.

Method Summary
void	clear() Atomically removes all of the elements from this queue.
int	drainTo(Collection<? super E> c) Removes all available elements from this queue and adds them to the given collection.
int	[drainTo](../../../java/util/concurrent/LinkedBlockingQueue.html#drainTo%28java.util.Collection, int%29)(Collection<? super E> c, int maxElements) Removes at most the given number of available elements from this queue and adds them to the given collection.
Iterator<E>	iterator() Returns an iterator over the elements in this queue in proper sequence.
boolean	offer(E e) Inserts the specified element at the tail of this queue if it is possible to do so immediately without exceeding the queue's capacity, returning true upon success and false if this queue is full.
boolean	[offer](../../../java/util/concurrent/LinkedBlockingQueue.html#offer%28E, long, java.util.concurrent.TimeUnit%29)(E e, long timeout,TimeUnit unit) Inserts the specified element at the tail of this queue, waiting if necessary up to the specified wait time for space to become available.
E	peek() Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.
E	poll() Retrieves and removes the head of this queue, or returns null if this queue is empty.
E	[poll](../../../java/util/concurrent/LinkedBlockingQueue.html#poll%28long, java.util.concurrent.TimeUnit%29)(long timeout,TimeUnit unit) Retrieves and removes the head of this queue, waiting up to the specified wait time if necessary for an element to become available.
void	put(E e) Inserts the specified element at the tail of this queue, waiting if necessary for space to become available.
int	remainingCapacity() Returns the number of additional elements that this queue can ideally (in the absence of memory or resource constraints) accept without blocking.
boolean	remove(Object o) Removes a single instance of the specified element from this queue, if it is present.
int	size() Returns the number of elements in this queue.
E	take() Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.
Object[]	toArray() Returns an array containing all of the elements in this queue, in proper sequence.
T[]	toArray(T[] a) Returns an array containing all of the elements in this queue, in proper sequence; the runtime type of the returned array is that of the specified array.
String	toString() Returns a string representation of this collection.

Methods inherited from class java.util.AbstractQueue
add, addAll, element, remove

Methods inherited from class java.util.AbstractCollection
contains, containsAll, isEmpty, removeAll, retainAll

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, [wait](../../../java/lang/Object.html#wait%28long, int%29)

Methods inherited from interface java.util.concurrent.BlockingQueue
add, contains

Methods inherited from interface java.util.Queue
element, remove

Methods inherited from interface java.util.Collection
addAll, containsAll, equals, hashCode, isEmpty, removeAll, retainAll

Constructor Detail

LinkedBlockingQueue

public LinkedBlockingQueue()

Creates a LinkedBlockingQueue with a capacity ofInteger.MAX_VALUE.

LinkedBlockingQueue

public LinkedBlockingQueue(int capacity)

Creates a LinkedBlockingQueue with the given (fixed) capacity.

Parameters:

capacity - the capacity of this queue

Throws:

[IllegalArgumentException](../../../java/lang/IllegalArgumentException.html "class in java.lang") - if capacity is not greater than zero

LinkedBlockingQueue

public LinkedBlockingQueue(Collection<? extends E> c)

Creates a LinkedBlockingQueue with a capacity ofInteger.MAX_VALUE, initially containing the elements of the given collection, added in traversal order of the collection's iterator.

Parameters:

c - the collection of elements to initially contain

Throws:

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if the specified collection or any of its elements are null

Method Detail

size

public int size()

Returns the number of elements in this queue.

Specified by:

[size](../../../java/util/Collection.html#size%28%29) in interface [Collection](../../../java/util/Collection.html "interface in java.util")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Specified by:

[size](../../../java/util/AbstractCollection.html#size%28%29) in class [AbstractCollection](../../../java/util/AbstractCollection.html "class in java.util")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Returns:

the number of elements in this queue

remainingCapacity

public int remainingCapacity()

Returns the number of additional elements that this queue can ideally (in the absence of memory or resource constraints) accept without blocking. This is always equal to the initial capacity of this queue less the current size of this queue.

Note that you cannot always tell if an attempt to insert an element will succeed by inspecting remainingCapacity because it may be the case that another thread is about to insert or remove an element.

Specified by:

[remainingCapacity](../../../java/util/concurrent/BlockingQueue.html#remainingCapacity%28%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Returns:

the remaining capacity

put

public void put(E e) throws InterruptedException

Inserts the specified element at the tail of this queue, waiting if necessary for space to become available.

Specified by:

[put](../../../java/util/concurrent/BlockingQueue.html#put%28E%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Parameters:

e - the element to add

Throws:

[InterruptedException](../../../java/lang/InterruptedException.html "class in java.lang") - if interrupted while waiting

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if the specified element is null

offer

public boolean offer(E e, long timeout, TimeUnit unit) throws InterruptedException

Inserts the specified element at the tail of this queue, waiting if necessary up to the specified wait time for space to become available.

Specified by:

[offer](../../../java/util/concurrent/BlockingQueue.html#offer%28E, long, java.util.concurrent.TimeUnit%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Parameters:

e - the element to add

timeout - how long to wait before giving up, in units ofunit

unit - a TimeUnit determining how to interpret thetimeout parameter

Returns:

true if successful, or false if the specified waiting time elapses before space is available.

Throws:

[InterruptedException](../../../java/lang/InterruptedException.html "class in java.lang") - if interrupted while waiting

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if the specified element is null

offer

public boolean offer(E e)

Inserts the specified element at the tail of this queue if it is possible to do so immediately without exceeding the queue's capacity, returning true upon success and false if this queue is full. When using a capacity-restricted queue, this method is generally preferable to method add, which can fail to insert an element only by throwing an exception.

Specified by:

[offer](../../../java/util/concurrent/BlockingQueue.html#offer%28E%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Specified by:

[offer](../../../java/util/Queue.html#offer%28E%29) in interface [Queue](../../../java/util/Queue.html "interface in java.util")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Parameters:

e - the element to add

Returns:

true if the element was added to this queue, elsefalse

Throws:

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if the specified element is null

take

public E take() throws InterruptedException

Description copied from interface: [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html#take%28%29)

Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.

Specified by:

[take](../../../java/util/concurrent/BlockingQueue.html#take%28%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Returns:

the head of this queue

Throws:

[InterruptedException](../../../java/lang/InterruptedException.html "class in java.lang") - if interrupted while waiting

poll

public E poll(long timeout, TimeUnit unit) throws InterruptedException

Description copied from interface: [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html#poll%28long, java.util.concurrent.TimeUnit%29)

Retrieves and removes the head of this queue, waiting up to the specified wait time if necessary for an element to become available.

Specified by:

[poll](../../../java/util/concurrent/BlockingQueue.html#poll%28long, java.util.concurrent.TimeUnit%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Parameters:

timeout - how long to wait before giving up, in units ofunit

unit - a TimeUnit determining how to interpret thetimeout parameter

Returns:

the head of this queue, or null if the specified waiting time elapses before an element is available

Throws:

[InterruptedException](../../../java/lang/InterruptedException.html "class in java.lang") - if interrupted while waiting

poll

public E poll()

Description copied from interface: [Queue](../../../java/util/Queue.html#poll%28%29)

Retrieves and removes the head of this queue, or returns null if this queue is empty.

Specified by:

[poll](../../../java/util/Queue.html#poll%28%29) in interface [Queue](../../../java/util/Queue.html "interface in java.util")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Returns:

the head of this queue, or null if this queue is empty

peek

public E peek()

Description copied from interface: [Queue](../../../java/util/Queue.html#peek%28%29)

Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.

Specified by:

[peek](../../../java/util/Queue.html#peek%28%29) in interface [Queue](../../../java/util/Queue.html "interface in java.util")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Returns:

the head of this queue, or null if this queue is empty

remove

public boolean remove(Object o)

Removes a single instance of the specified element from this queue, if it is present. More formally, removes an element e such that o.equals(e), if this queue contains one or more such elements. Returns true if this queue contained the specified element (or equivalently, if this queue changed as a result of the call).

Specified by:

[remove](../../../java/util/Collection.html#remove%28java.lang.Object%29) in interface [Collection](../../../java/util/Collection.html "interface in java.util")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Specified by:

[remove](../../../java/util/concurrent/BlockingQueue.html#remove%28java.lang.Object%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Overrides:

[remove](../../../java/util/AbstractCollection.html#remove%28java.lang.Object%29) in class [AbstractCollection](../../../java/util/AbstractCollection.html "class in java.util")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Parameters:

o - element to be removed from this queue, if present

Returns:

true if this queue changed as a result of the call

toArray

public Object[] toArray()

Returns an array containing all of the elements in this queue, in proper sequence.

The returned array will be "safe" in that no references to it are maintained by this queue. (In other words, this method must allocate a new array). The caller is thus free to modify the returned array.

This method acts as bridge between array-based and collection-based APIs.

Specified by:

[toArray](../../../java/util/Collection.html#toArray%28%29) in interface [Collection](../../../java/util/Collection.html "interface in java.util")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Overrides:

[toArray](../../../java/util/AbstractCollection.html#toArray%28%29) in class [AbstractCollection](../../../java/util/AbstractCollection.html "class in java.util")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Returns:

an array containing all of the elements in this queue

toArray

public T[] toArray(T[] a)

Returns an array containing all of the elements in this queue, in proper sequence; the runtime type of the returned array is that of the specified array. If the queue fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this queue.

If this queue fits in the specified array with room to spare (i.e., the array has more elements than this queue), the element in the array immediately following the end of the queue is set tonull.

Like the toArray() method, this method acts as bridge between array-based and collection-based APIs. Further, this method allows precise control over the runtime type of the output array, and may, under certain circumstances, be used to save allocation costs.

Suppose x is a queue known to contain only strings. The following code can be used to dump the queue into a newly allocated array of String:

 String[] y = x.toArray(new String[0]);

Note that toArray(new Object[0]) is identical in function totoArray().

Specified by:

[toArray](../../../java/util/Collection.html#toArray%28T[]%29) in interface [Collection](../../../java/util/Collection.html "interface in java.util")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Overrides:

[toArray](../../../java/util/AbstractCollection.html#toArray%28T[]%29) in class [AbstractCollection](../../../java/util/AbstractCollection.html "class in java.util")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Parameters:

a - the array into which the elements of the queue are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose

Returns:

an array containing all of the elements in this queue

Throws:

[ArrayStoreException](../../../java/lang/ArrayStoreException.html "class in java.lang") - if the runtime type of the specified array is not a supertype of the runtime type of every element in this queue

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if the specified array is null

toString

public String toString()

Description copied from class: [AbstractCollection](../../../java/util/AbstractCollection.html#toString%28%29)

Returns a string representation of this collection. The string representation consists of a list of the collection's elements in the order they are returned by its iterator, enclosed in square brackets ("[]"). Adjacent elements are separated by the characters", " (comma and space). Elements are converted to strings as by String.valueOf(Object).

Overrides:

[toString](../../../java/util/AbstractCollection.html#toString%28%29) in class [AbstractCollection](../../../java/util/AbstractCollection.html "class in java.util")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Returns:

a string representation of this collection

clear

public void clear()

Atomically removes all of the elements from this queue. The queue will be empty after this call returns.

Specified by:

[clear](../../../java/util/Collection.html#clear%28%29) in interface [Collection](../../../java/util/Collection.html "interface in java.util")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Overrides:

[clear](../../../java/util/AbstractQueue.html#clear%28%29) in class [AbstractQueue](../../../java/util/AbstractQueue.html "class in java.util")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

drainTo

public int drainTo(Collection<? super E> c)

Description copied from interface: [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html#drainTo%28java.util.Collection%29)

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 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 inIllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.

Specified by:

[drainTo](../../../java/util/concurrent/BlockingQueue.html#drainTo%28java.util.Collection%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Parameters:

c - the collection to transfer elements into

Returns:

the number of elements transferred

Throws:

[UnsupportedOperationException](../../../java/lang/UnsupportedOperationException.html "class in java.lang") - if addition of elements is not supported by the specified collection

[ClassCastException](../../../java/lang/ClassCastException.html "class in java.lang") - if the class of an element of this queue prevents it from being added to the specified collection

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if the specified collection is null

[IllegalArgumentException](../../../java/lang/IllegalArgumentException.html "class in java.lang") - 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

drainTo

public int drainTo(Collection<? super E> c, int maxElements)

Description copied from interface: [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html#drainTo%28java.util.Collection, int%29)

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 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 inIllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.

Specified by:

[drainTo](../../../java/util/concurrent/BlockingQueue.html#drainTo%28java.util.Collection, int%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Parameters:

c - the collection to transfer elements into

maxElements - the maximum number of elements to transfer

Returns:

the number of elements transferred

Throws:

[UnsupportedOperationException](../../../java/lang/UnsupportedOperationException.html "class in java.lang") - if addition of elements is not supported by the specified collection

[ClassCastException](../../../java/lang/ClassCastException.html "class in java.lang") - if the class of an element of this queue prevents it from being added to the specified collection

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if the specified collection is null

iterator

public Iterator<E> iterator()

Returns an iterator over the elements in this queue in proper sequence. The returned Iterator is a "weakly consistent" iterator that will never throw ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

Specified by:

[iterator](../../../java/lang/Iterable.html#iterator%28%29) in interface [Iterable](../../../java/lang/Iterable.html "interface in java.lang")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Specified by:

[iterator](../../../java/util/Collection.html#iterator%28%29) in interface [Collection](../../../java/util/Collection.html "interface in java.util")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Specified by:

[iterator](../../../java/util/AbstractCollection.html#iterator%28%29) in class [AbstractCollection](../../../java/util/AbstractCollection.html "class in java.util")<[E](../../../java/util/concurrent/LinkedBlockingQueue.html "type parameter in LinkedBlockingQueue")>

Returns:

an iterator over the elements in this queue in proper sequence

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