Added in API level 1

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 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.

Summary

Public constructors

LinkedBlockingQueue()

Creates a LinkedBlockingQueue with a capacity of Integer.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 Integer.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.

void forEach(Consumer<? super E> action)
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.

boolean removeAll(Collection<?> c)

Removes all of this collection's elements that are also contained in the specified collection (optional operation).

boolean removeIf(Predicate<? super E> filter)

Removes all of the elements of this collection that satisfy the given predicate.

boolean retainAll(Collection<?> c)

Retains only the elements in this collection that are contained in the specified collection (optional operation).

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

boolean add(E e)

Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions, returning true upon success and throwing an IllegalStateException if no space is currently available.

boolean addAll(Collection<? extends E> c)

Adds all of the elements in the specified collection to this queue.

void clear()

Removes all of the elements from this queue.

E element()

Retrieves, but does not remove, the head of this queue.

E remove()

Retrieves and removes the head of this queue.

boolean add(E e)

Ensures that this collection contains the specified element (optional operation).

boolean addAll(Collection<? extends E> c)

Adds all of the elements in the specified collection to this collection (optional operation).

void clear()

Removes all of the elements from this collection (optional operation).

boolean contains(Object o)

Returns true if this collection contains the specified element.

boolean containsAll(Collection<?> c)

Returns true if this collection contains all of the elements in the specified collection.

boolean isEmpty()

Returns true if this collection contains no elements.

abstract Iterator<E> iterator()

Returns an iterator over the elements contained in this collection.

boolean remove(Object o)

Removes a single instance of the specified element from this collection, if it is present (optional operation).

boolean removeAll(Collection<?> c)

Removes all of this collection's elements that are also contained in the specified collection (optional operation).

boolean retainAll(Collection<?> c)

Retains only the elements in this collection that are contained in the specified collection (optional operation).

abstract int size()

Returns the number of elements in this collection.

<T> T[] toArray(T[] a)

Returns an array containing all of the elements in this collection; 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 collection.

String toString()

Returns a string representation of this collection.

Object clone()

Creates and returns a copy of this object.

boolean equals(Object obj)

Indicates whether some other object is "equal to" this one.

void finalize()

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.

final Class<?> getClass()

Returns the runtime class of this Object.

int hashCode()

Returns a hash code value for the object.

final void notify()

Wakes up a single thread that is waiting on this object's monitor.

final void notifyAll()

Wakes up all threads that are waiting on this object's monitor.

String toString()

Returns a string representation of the object.

final void wait(long timeoutMillis, int nanos)

Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.

final void wait(long timeoutMillis)

Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.

final void wait()

Causes the current thread to wait until it is awakened, typically by being notified or interrupted.

abstract boolean add(E e)

Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions, returning true upon success and throwing an IllegalStateException if no space is currently available.

abstract E element()

Retrieves, but does not remove, the head of this queue.

abstract boolean offer(E e)

Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions.

abstract E peek()

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

abstract E poll()

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

abstract E remove()

Retrieves and removes the head of this queue.

abstract boolean add(E e)

Ensures that this collection contains the specified element (optional operation).

abstract boolean addAll(Collection<? extends E> c)

Adds all of the elements in the specified collection to this collection (optional operation).

abstract void clear()

Removes all of the elements from this collection (optional operation).

abstract boolean contains(Object o)

Returns true if this collection contains the specified element.

abstract boolean containsAll(Collection<?> c)

Returns true if this collection contains all of the elements in the specified collection.

abstract boolean equals(Object o)

Compares the specified object with this collection for equality.

abstract int hashCode()

Returns the hash code value for this collection.

abstract boolean isEmpty()

Returns true if this collection contains no elements.

abstract Iterator<E> iterator()

Returns an iterator over the elements in this collection.

default Stream<E> parallelStream()

Returns a possibly parallel Stream with this collection as its source.

abstract boolean remove(Object o)

Removes a single instance of the specified element from this collection, if it is present (optional operation).

abstract boolean removeAll(Collection<?> c)

Removes all of this collection's elements that are also contained in the specified collection (optional operation).

default boolean removeIf(Predicate<? super E> filter)

Removes all of the elements of this collection that satisfy the given predicate.

abstract boolean retainAll(Collection<?> c)

Retains only the elements in this collection that are contained in the specified collection (optional operation).

abstract int size()

Returns the number of elements in this collection.

default Spliterator<E> spliterator()

Creates a Spliterator over the elements in this collection.

default Stream<E> stream()

Returns a sequential Stream with this collection as its source.

abstract <T> T[] toArray(T[] a)

Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array.

abstract Object[] toArray()

Returns an array containing all of the elements in this collection.

default <T> T[] toArray(IntFunction<T[]> generator)

Returns an array containing all of the elements in this collection, using the provided generator function to allocate the returned array.

abstract boolean add(E e)

Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions, returning true upon success and throwing an IllegalStateException if no space is currently available.

abstract boolean contains(Object o)

Returns true if this queue contains the specified element.

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

Removes all available elements from this queue and adds them to the given collection.

abstract 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.

abstract boolean offer(E e)

Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions, returning true upon success and false if no space is currently available.

abstract boolean offer(E e, long timeout, TimeUnit unit)

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

abstract 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.

abstract void put(E e)

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

abstract int remainingCapacity()

Returns the number of additional elements that this queue can ideally (in the absence of memory or resource constraints) accept without blocking, or Integer.MAX_VALUE if there is no intrinsic limit.

abstract boolean remove(Object o)

Removes a single instance of the specified element from this queue, if it is present.

abstract E take()

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

default void forEach(Consumer<? super T> action)

Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception.

abstract Iterator<E> iterator()

Returns an iterator over elements of type T.

default Spliterator<E> spliterator()

Creates a Spliterator over the elements described by this Iterable.

Public constructors

LinkedBlockingQueue

Added in API level 1
public LinkedBlockingQueue ()

Creates a LinkedBlockingQueue with a capacity of Integer.MAX_VALUE.

LinkedBlockingQueue

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

Creates a LinkedBlockingQueue with a capacity of Integer.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
public 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
public 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
public 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

drainTo

Added in API level 1
public 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

forEach

Added in API level 24
public void forEach (Consumer<? super E> action)

Parameters
action Consumer

iterator

Added in API level 1
public 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
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.

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
public 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

peek

Added in API level 1
public 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
public 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

poll

Added in API level 1
public 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
public 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

remainingCapacity

Added in API level 1
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.

Returns
int the remaining capacity

remove

Added in API level 1
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).

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

removeAll

Added in API level 1
public boolean removeAll (Collection<?> c)

Removes all of this collection's elements that are also contained in the specified collection (optional operation). After this call returns, this collection will contain no elements in common with the specified collection.

Parameters
c Collection: collection containing elements to be removed from this collection

Returns
boolean true if this collection changed as a result of the call

removeIf

Added in API level 24
public boolean removeIf (Predicate<? super E> filter)

Removes all of the elements of this collection that satisfy the given predicate. Errors or runtime exceptions thrown during iteration or by the predicate are relayed to the caller.

Parameters
filter Predicate: a predicate which returns true for elements to be removed

Returns
boolean true if any elements were removed

retainAll

Added in API level 1
public boolean retainAll (Collection<?> c)

Retains only the elements in this collection that are contained in the specified collection (optional operation). In other words, removes from this collection all of its elements that are not contained in the specified collection.

Parameters
c Collection: collection containing elements to be retained in this collection

Returns
boolean true if this collection changed as a result of the call

size

Added in API level 1
public 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
public Spliterator<E> spliterator ()

Returns a Spliterator over the elements in this queue.

The returned spliterator is weakly consistent.

The Spliterator reports Spliterator.CONCURRENT, Spliterator.ORDERED, and Spliterator.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
public 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

toArray

Added in API level 1
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 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
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.

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

toString

Added in API level 1
public 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 String.valueOf(Object).

Returns
String a string representation of this collection