Summary: Ctors | Methods | Inherited Methods | [Expand All]

public class

ConcurrentLinkedQueue

extends AbstractQueue<E>
implements Serializable Queue<E>

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

Class Overview

An unbounded thread-safe 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. A ConcurrentLinkedQueue is an appropriate choice when many threads will share access to a common collection. This queue does not permit null elements.

This implementation employs an efficient "wait-free" algorithm based on one described in Simple, Fast, and Practical Non-Blocking and Blocking Concurrent Queue Algorithms by Maged M. Michael and Michael L. Scott.

Beware that, unlike in most collections, the size method is NOT a constant-time operation. Because of the asynchronous nature of these queues, determining the current number of elements requires a traversal of the elements.

This class implements all of the optional methods of the Collection and Iterator interfaces.

Summary

Public Constructors
	ConcurrentLinkedQueue() Creates a `ConcurrentLinkedQueue` that is initially empty.
	ConcurrentLinkedQueue(Collection<? extends E> c) Creates a `ConcurrentLinkedQueue` initially containing the elements of the given collection, added in traversal order of the collection's iterator.

Public Methods
boolean	add(E o) Adds the specified element to the tail of this queue.
boolean	contains(Object o) Searches this Collection for the specified object.
boolean	isEmpty() Returns true if the collection has no element, otherwise false.
Iterator<E>	iterator() Returns an iterator over the elements in this queue in proper sequence.
boolean	offer(E o) Inserts the specified element to the tail of this queue.
E	peek() Gets but not removes the element in the head of the queue, or throws exception if there is no element in the queue.
E	poll() Gets and removes the element in the head of the queue, or returns null if there is no element in the queue.
boolean	remove(Object o) Removes the first occurrence of the specified object from this Collection.
int	size() Returns the number of elements in this queue.
<T> T[]	toArray(T[] a) Returns an array containing all elements contained in this Collection.
Object[]	toArray() Returns a new array containing all elements contained in this Collection.

[Expand]

Inherited Methods

From class java.util.AbstractQueue

From class java.util.AbstractCollection

boolean	add(E object) If the specified element is not contained within this collection, and addition of this element succeeds, then true will be returned.
boolean	addAll(Collection<? extends E> collection) Adds the objects in the specified Collection to this Collection.
void	clear() Removes all the elements in this collection.
boolean	contains(Object object) Searches this Collection for the specified object.
boolean	containsAll(Collection<?> collection) Searches this Collection for all objects in the specified Collection.
boolean	isEmpty() Returns true if the collection has no element, otherwise false.
abstract Iterator<E>	iterator() Returns an Iterator on the elements of this Collection.
boolean	remove(Object object) Removes the first occurrence of the specified object from this Collection.
boolean	removeAll(Collection<?> collection) Removes all occurrences in this Collection of each object in the specified Collection.
boolean	retainAll(Collection<?> collection) Removes all objects from this Collection that are not contained in the specified Collection.
abstract int	size() Returns the number of elements in this Collection.
<T> T[]	toArray(T[] contents) Returns an array containing all elements contained in this Collection.
Object[]	toArray() Returns a new array containing all elements contained in this Collection.
String	toString() Returns the string representation of this Collection.

From class java.lang.Object

Object	clone() Returns a new instance of the same class as the receiver, whose slots have been filled in with the values in the slots of the receiver.
boolean	equals(Object o) Compares the argument to the receiver, and returns true if they represent the same object using a class specific comparison.
void	finalize() Called by the virtual machine when there are no longer any (non-weak) references to the receiver.
final Class<? extends Object>	getClass() Returns the unique instance of java.lang.Class which represents the class of the receiver.
int	hashCode() Returns an integer hash code for the receiver.
final void	notify() Causes one thread which is `wait` ing on the receiver to be made ready to run.
final void	notifyAll() Causes all threads which are `wait` ing on the receiver to be made ready to run.
String	toString() Returns a string containing a concise, human-readable description of the receiver.
final void	wait(long time, int frac) Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by `notify` or `notifyAll`) or the expiration of the timeout.
final void	wait(long time) Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by `notify` or `notifyAll`) or the expiration of the timeout.
final void	wait() Causes the thread which sent this message to be made not ready to run pending some change in the receiver (as indicated by `notify` or `notifyAll`).

From interface java.lang.Iterable

From interface java.util.Collection

abstract boolean	add(E object) Attempts to add `object` to the contents of this `Collection`.
abstract boolean	addAll(Collection<? extends E> collection) Attempts to add all of the objects contained in `collection` to the contents of this collection.
abstract void	clear() Removes all elements from this Collection, leaving it empty.
abstract boolean	contains(Object object) Searches this Collection for the specified object.
abstract boolean	containsAll(Collection<?> collection) Searches this Collection for all objects in the specified Collection.
abstract boolean	equals(Object object) Compares the argument to the receiver, and returns true if they represent the same object using a class specific comparison.
abstract int	hashCode() Returns an integer hash code for the receiver.
abstract boolean	isEmpty() Returns if this Collection has no elements, a size of zero.
abstract Iterator<E>	iterator() Returns an instance of Iterator that may be used to access the objects contained by this collection.
abstract boolean	remove(Object object) Removes the first occurrence of the specified object from this Collection.
abstract boolean	removeAll(Collection<?> collection) Removes all occurrences in this Collection of each object in the specified Collection.
abstract boolean	retainAll(Collection<?> collection) Removes all objects from this Collection that are not also found in the contents of `collection`.
abstract int	size() Returns a count of how many objects are contained by this collection.
abstract <T> T[]	toArray(T[] array) Returns an array containing all elements contained in this Collection.
abstract Object[]	toArray() Returns a new array containing all elements contained in this Collection.

From interface java.util.Queue

Public Constructors

public ConcurrentLinkedQueue ()

Creates a ConcurrentLinkedQueue that is initially empty.

public ConcurrentLinkedQueue (Collection<? extends E> c)

Creates a ConcurrentLinkedQueue 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 `c` or any element within it is `null`

Public Methods

public boolean add (E o)

Adds the specified element to the tail of this queue.

Parameters

o	the element to add.

Returns

true (as per the general contract of Collection.add).

Throws

NullPointerException	if the specified element is `null`

public boolean contains (Object o)

Searches this Collection for the specified object.

Parameters

o	the object to search for

Returns

true if object is an element of this Collection, false otherwise

public boolean isEmpty ()

Returns true if the collection has no element, otherwise false.

Returns

true if the collection has no element.

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.

Returns

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

public boolean offer (E o)

Inserts the specified element to the tail of this queue.

Parameters

o	the element to add.

Returns

true (as per the general contract of Queue.offer).

Throws

NullPointerException	if the specified element is `null`

public E peek ()

Gets but not removes the element in the head of the queue, or throws exception if there is no element in the queue.

Returns

the element in the head of the queue or null if there is no element in the queue.

public E poll ()

Gets and removes the element in the head of the queue, or returns null if there is no element in the queue.

Returns

the element in the head of the queue or null if there is no element in the queue.

public boolean remove (Object o)

Removes the first occurrence of the specified object from this Collection. This operation traverses over the collection, looking for the specified object. Once the object is found, the object will be removed from the collection using the iterator's remove method. This collection will throw an UnsupportedOperationException if the iterator returned does not implement remove method, and the specified object is in this collection.

Parameters

o	the object to remove

Returns

true if this Collection is modified, false otherwise

public int size ()

Returns the number of elements in this queue. If this queue contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

Beware that, unlike in most collections, this method is NOT a constant-time operation. Because of the asynchronous nature of these queues, determining the current number of elements requires an O(n) traversal.

Returns

the number of elements in this queue.

public T[] toArray (T[] a)

Returns an array containing all elements contained in this Collection. If the specified array is large enough to hold the elements, the specified array is used, otherwise an array of the same type is created. If the specified array is used and is larger than this Collection, the array element following the collection elements is set to null.

Parameters

a	the array

Returns

an array of the elements from this Collection

public Object[] toArray ()

Returns a new array containing all elements contained in this Collection. All the elements in the array will not be referenced by the collection. The elements in the returned array will be sorted to the same order as those returned by the iterator of this collection itself if the collection guarantees the order.

Returns

an array of the elements from this Collection

Feb	MAR	Apr
	22
2008	2009	2010

Interfaces

Classes

Enums

Exceptions

ConcurrentLinkedQueue

Class Overview

Summary

Public Constructors

public ConcurrentLinkedQueue ()

public ConcurrentLinkedQueue (Collection<? extends E> c)

Parameters

Throws

Public Methods

public boolean add (E o)

Parameters

Returns

Throws

public boolean contains (Object o)

Parameters

Returns

public boolean isEmpty ()

Returns

public Iterator<E> iterator ()

Returns

public boolean offer (E o)

Parameters

Returns

Throws

public E peek ()

Returns

public E poll ()

Returns

public boolean remove (Object o)

Parameters

Returns

public int size ()

Returns

public T[] toArray (T[] a)

Parameters

Returns

public Object[] toArray ()

Returns