java.util.concurrent
Class LinkedBlockingQueue<E>

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

Type Parameters:

E - the type of elements held in this collection

All Implemented Interfaces:

Serializable , Iterable <E>, Collection <E>, BlockingQueue <E>, Queue <E>

public class LinkedBlockingQueue<E>
extends AbstractQueue<E>
implements BlockingQueue<E>, 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 of Integer.MAX_VALUE .
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.
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           Removes all available elements from this queue and adds them to into the given collection.
int	drainTo ( Collection <? super E           Removes at most the given number of available elements from this queue and adds them to into the given collection.
Iterator < E >	iterator ()           Returns an iterator over the elements in this queue in proper sequence.
boolean	offer ( E           Inserts the specified element at the tail of this queue if it is possible to do so possible, returning immediately without exceeding the queue's capacity, returning true upon success and false if this queue is full.
boolean	offer ( E  e,  o, long timeout, TimeUnit           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 returning 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 (long timeout, TimeUnit           Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time if necessary for an element to become available. no elements are present on this queue.
void	put ( E           Inserts           Adds the specified element at to 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. no elements are present on this queue.
Object	toArray ()           Returns an array containing all of the elements in this queue, in proper sequence. collection.
<T> T[]	toArray (T[] a)           Returns an array containing all of the elements in this queue, in proper sequence; collection; 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

 

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 , contains , containsAll , equals , hashCode , isEmpty , removeAll , retainAll

 

Constructor Detail

LinkedBlockingQueue

public LinkedBlockingQueue()

Creates a LinkedBlockingQueue with a capacity of Integer.MAX_VALUE .

LinkedBlockingQueue

public LinkedBlockingQueue(int capacity)

Creates a LinkedBlockingQueue with the given (fixed) capacity.

Parameters:

capacity - the capacity of this queue queue.

Throws:

IllegalArgumentException - if capacity is not greater than zero zero.

LinkedBlockingQueue

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 - the collection of elements to initially contain

Throws:

NullPointerException - if the specified collection or any of its elements are null - if c or any element within it is null

size

public int size()

Returns the number of elements in this queue.

Specified by:

size in interface Collection < E >

Specified by:

size in class AbstractCollection < E >

Returns:

the number of elements in this queue 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 add an element will succeed by inspecting remainingCapacity because it may be the case that another thread is about to insert or remove an element. because it may be the case that a waiting consumer is ready to take an element out of an otherwise full queue.

Specified by:

remainingCapacity in interface BlockingQueue < E >

Returns:

the remaining capacity

put

public void put(E e)
  o)
 throws InterruptedException

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

Specified by:

put in interface BlockingQueue < E >

Parameters:

e o - the element to add

Throws:

InterruptedException - if interrupted while waiting waiting.

NullPointerException - if the specified element is null .

offer

public boolean offer(E e,
  o,
 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 in interface BlockingQueue < E >

Parameters:

e o - the element to add

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

unit - a TimeUnit determining how to interpret the timeout parameter

Returns:

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

Throws:

InterruptedException - if interrupted while waiting waiting.

NullPointerException - if the specified element is null .

offer

public boolean offer(E e)  o) 

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. Inserts the specified element at the tail of this queue if possible, returning immediately if this queue is full.

Specified by:

offer in interface BlockingQueue < E >

Specified by:

offer in interface Queue < E >

Parameters:

e o - the element to add add.

Returns:

true if it was possible to add the element was added to this queue, else false

Throws:

NullPointerException - if the specified element is null

take

public E take()
       throws InterruptedException

Description copied from interface: BlockingQueue

Retrieves and removes the head of this queue, waiting if necessary until an element becomes available. no elements are present on this queue.

Specified by:

take in interface BlockingQueue < E >

Returns:

the head of this queue

Throws:

InterruptedException - if interrupted while waiting waiting.

poll

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

Description copied from interface: BlockingQueue

Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time if necessary for an element to become available. no elements are present on this queue.

Specified by:

poll in interface BlockingQueue < E >

Parameters:

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

unit - a TimeUnit determining how to interpret the timeout parameter

Returns:

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

Throws:

InterruptedException - if interrupted while waiting waiting.

poll

public E poll()

Description copied from interface: Queue

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

Specified by:

poll in interface Queue < E >

Returns:

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

peek

public E peek()

Description copied from interface: Queue

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

Specified by:

peek in interface Queue < E >

Returns:

the head of this queue, or null if this queue is empty 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 in interface Collection < E >

Specified by:

remove in interface BlockingQueue < E >

Overrides:

remove in class AbstractCollection < E >

Parameters:

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

Returns:

true if this queue changed as a result of the call if the collection contained the specified element.

toArray

public Object[] toArray()

Description copied from class: AbstractCollection

Returns an array containing all of the elements in this queue, collection. If the collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in proper sequence.

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

This method acts as bridge between array-based and collection-based APIs. This implementation allocates the array to be returned, and iterates over the elements in the collection, storing each object reference in the next consecutive element of the array, starting with element 0.

Specified by:

toArray in interface Collection < E >

Overrides:

toArray in class AbstractCollection < E >

Returns:

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

toArray

public <T> T[] toArray(T[] a)

Description copied from class: AbstractCollection

Returns an array containing all of the elements in this queue, in proper sequence; collection; the runtime type of the returned array is that of the specified array. If the queue collection 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. collection.

If this queue the collection fits in the specified array with room to spare (i.e., the array has more elements than this queue), the collection), the element in the array immediately following the end of the queue collection is set to null . This is useful in determining the length of the collection only if the caller knows that the collection does not contain any null elements.)

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. If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.

Suppose This implementation checks if the array is large enough to contain the collection; if not, it allocates a new array of the correct size and type (using reflection). Then, it iterates over the collection, storing each object reference in the next consecutive element of the array, starting with element 0. If the array is larger than the collection, a x null 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() . is stored in the first location after the end of the collection.

Specified by:

toArray in interface Collection < E >

Overrides:

toArray in class AbstractCollection < E >

Parameters:

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

Returns:

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 an array containing the elements of the collection.

toString

public String toString()

Description copied from class: AbstractCollection

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) String.valueOf(Object) .

This implementation creates an empty string buffer, appends a left square bracket, and iterates over the collection appending the string representation of each element in turn. After appending each element except the last, the string ", " is appended. Finally a right bracket is appended. A string is obtained from the string buffer, and returned.

Overrides:

toString in class AbstractCollection < E >

Returns:

a string representation of this collection 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 in interface Collection < E >

Overrides:

clear in class AbstractQueue < E >

drainTo

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

Description copied from interface: BlockingQueue

Removes all available elements from this queue and adds them to into the given collection. This operation may be more efficient than repeatedly polling this queue. A failure encountered while attempting to add elements to collection 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.

Specified by:

drainTo in interface BlockingQueue < E >

Parameters:

c - the collection to transfer elements into

Returns:

the number of elements transferred

Throws:

UnsupportedOperationException - if addition of elements is not supported by the specified collection

ClassCastException - if the class of an element of this queue prevents it from being added to the specified collection

NullPointerException - if the specified collection is null

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 the number of elements transferred.

drainTo

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

Description copied from interface: BlockingQueue

Removes at most the given number of available elements from this queue and adds them to into the given collection. A failure encountered while attempting to add elements to collection 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.

Specified by:

drainTo in interface BlockingQueue < E >

Parameters:

c - the collection to transfer elements into

maxElements - the maximum number of elements to transfer

Returns:

the number of elements transferred

Throws:

UnsupportedOperationException - if addition of elements is not supported by the specified collection

ClassCastException - if the class of an element of this queue prevents it from being added to the specified collection

NullPointerException - if the specified collection is null

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 the number of elements transferred.

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 in interface Iterable < E >

Specified by:

iterator in interface Collection < E >

Specified by:

iterator in class AbstractCollection < E >

Returns:

an iterator over the elements in this queue in proper sequence sequence.