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LinkedBlockingQueue

public class LinkedBlockingQueue
extends AbstractQueue<E> implements BlockingQueue<E>, Serializable

java.lang.Object
   ↳ java.util.AbstractCollection<E>
     ↳ java.util.AbstractQueue<E>
       ↳ java.util.concurrent.LinkedBlockingQueue<E>


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 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.

Summary

Public constructors

LinkedBlockingQueue()

Creates a LinkedBlockingQueue with a capacity of MAX_VALUE.

LinkedBlockingQueue(int capacity)

Creates a LinkedBlockingQueue with the given (fixed) capacity.

LinkedBlockingQueue(Collection<? extends E> c)

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

Public methods

void clear()

Atomically removes all of the elements from this queue.

boolean contains(Object o)

Returns true if this queue contains the specified element.

int drainTo(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.

int drainTo(Collection<? super E> c)

Removes all 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(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(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.

E poll()

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

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.

Spliterator<E> spliterator()

Returns a Spliterator over the elements in this queue.

E take()

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

<T> 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.

Object[] toArray()

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

String toString()

Returns a string representation of this collection.

Inherited methods

From class java.util.AbstractQueue
From class java.util.AbstractCollection
From class java.lang.Object
From interface java.util.Queue
From interface java.util.Collection
From interface java.util.concurrent.BlockingQueue
From interface java.lang.Iterable

Public constructors

LinkedBlockingQueue

Added in API level 1
LinkedBlockingQueue ()

Creates a LinkedBlockingQueue with a capacity of MAX_VALUE.

LinkedBlockingQueue

Added in API level 1
LinkedBlockingQueue (int capacity)

Creates a LinkedBlockingQueue with the given (fixed) capacity.

Parameters
capacity int: the capacity of this queue
Throws
IllegalArgumentException if capacity is not greater than zero

LinkedBlockingQueue

Added in API level 1
LinkedBlockingQueue (Collection<? extends E> c)

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

Parameters
c Collection: the collection of elements to initially contain
Throws
NullPointerException if the specified collection or any of its elements are null

Public methods

clear

Added in API level 1
void clear ()

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

contains

Added in API level 1
boolean contains (Object o)

Returns true if this queue contains the specified element. More formally, returns true if and only if this queue contains at least one element e such that o.equals(e).

Parameters
o Object: object to be checked for containment in this queue
Returns
boolean true if this queue contains the specified element

drainTo

Added in API level 1
int drainTo (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. 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 in IllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.

Parameters
c Collection: the collection to transfer elements into
maxElements int: the maximum number of elements to transfer
Returns
int the number of elements transferred
Throws
UnsupportedOperationException
ClassCastException
NullPointerException
IllegalArgumentException

drainTo

Added in API level 1
int drainTo (Collection<? super E> c)

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

Parameters
c Collection: the collection to transfer elements into
Returns
int the number of elements transferred
Throws
UnsupportedOperationException
ClassCastException
NullPointerException
IllegalArgumentException

iterator

Added in API level 1
Iterator<E> iterator ()

Returns an iterator over the elements in this queue in proper sequence. The elements will be returned in order from first (head) to last (tail).

The returned iterator is weakly consistent.

Returns
Iterator<E> an iterator over the elements in this queue in proper sequence

offer

Added in API level 1
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.

Parameters
e E: the element to add
Returns
boolean true if the element was added to this queue, else false
Throws
NullPointerException if the specified element is null

offer

Added in API level 1
boolean offer (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.

Parameters
e E: the element to add
timeout long: how long to wait before giving up, in units of unit
unit TimeUnit: a TimeUnit determining how to interpret the timeout parameter
Returns
boolean true if successful, or false if the specified waiting time elapses before space is available
Throws
InterruptedException
NullPointerException

peek

Added in API level 1
E peek ()

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

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

poll

Added in API level 1
E poll (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.

Parameters
timeout long: how long to wait before giving up, in units of unit
unit TimeUnit: a TimeUnit determining how to interpret the timeout parameter
Returns
E the head of this queue, or null if the specified waiting time elapses before an element is available
Throws
InterruptedException

poll

Added in API level 1
E poll ()

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

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

put

Added in API level 1
void put (E e)

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

Parameters
e E: the element to add
Throws
InterruptedException
NullPointerException

remainingCapacity

Added in API level 1
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.

Returns
int the remaining capacity

remove

Added in API level 1
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).

Parameters
o Object: element to be removed from this queue, if present
Returns
boolean true if this queue changed as a result of the call

size

Added in API level 1
int size ()

Returns the number of elements in this queue.

Returns
int the number of elements in this queue

spliterator

Added in API level 24
Spliterator<E> spliterator ()

Returns a Spliterator over the elements in this queue.

The returned spliterator is weakly consistent.

The Spliterator reports CONCURRENT, ORDERED, and NONNULL.

Implementation Note:
  • The Spliterator implements trySplit to permit limited parallelism.
Returns
Spliterator<E> a Spliterator over the elements in this queue

take

Added in API level 1
E take ()

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

Returns
E the head of this queue
Throws
InterruptedException

toArray

Added in API level 1
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 to null.

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 to toArray().

Parameters
a T: 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
T[] an array containing all of the elements in this queue
Throws
ArrayStoreException if the runtime type of the specified array is not a supertype of the runtime type of every element in this queue
NullPointerException if the specified array is null

toArray

Added in API level 1
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.

Returns
Object[] an array containing all of the elements in this queue

toString

Added in API level 1
String toString ()

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 valueOf(Object).

Returns
String a string representation of this collection
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