程序包 java.util.concurrent

类 ConcurrentLinkedQueue<E>

java.lang.Object

java.util.AbstractCollection<E>

java.util.AbstractQueue<E>

java.util.concurrent.ConcurrentLinkedQueue<E>

类型参数:

E - the type of elements held in this collection

所有已实现的接口:

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

public class ConcurrentLinkedQueue<E>
extends AbstractQueue<E>
implements Queue<E>, Serializable

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. Like most other concurrent collection implementations, this class does not permit the use of null elements.

This implementation employs an efficient non-blocking 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.

Iterators are weakly consistent, returning elements reflecting the state of the queue at some point at or since the creation of the iterator. They do not throw ConcurrentModificationException, and may proceed concurrently with other operations. Elements contained in the queue since the creation of the iterator will be returned exactly once.

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, and so may report inaccurate results if this collection is modified during traversal. Additionally, the bulk operations addAll, removeAll, retainAll, containsAll, equals, and toArray are not guaranteed to be performed atomically. For example, an iterator operating concurrently with an addAll operation might view only some of the added elements.

This class and its iterator implement all of the optional methods of the Queue and Iterator interfaces.

Memory consistency effects: As with other concurrent collections, actions in a thread prior to placing an object into a ConcurrentLinkedQueue happen-before actions subsequent to the access or removal of that element from the ConcurrentLinkedQueue in another thread.

This class is a member of the Java Collections Framework.

从以下版本开始:

1.5

另请参阅:

序列化表格

构造器概要

构造器

构造器	说明
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.

方法概要

限定符和类型	方法	说明
boolean	add(E e)	Inserts the specified element at the tail of this queue.
boolean	addAll(Collection<? extends E> c)	Appends all of the elements in the specified collection to the end of this queue, in the order that they are returned by the specified collection's iterator.
boolean	contains(Object o)	Returns true if this queue contains the specified element.
boolean	isEmpty()	Returns true if this queue contains no elements.
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.
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.
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.
Object[]	toArray()	Returns an array containing all of the elements in this queue, in proper sequence.
<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.

从类继承的方法 java.util.AbstractCollection

containsAll, removeAll, retainAll, toString

从类继承的方法 java.util.AbstractQueue

clear, element, remove

从接口继承的方法 java.util.Collection

clear, containsAll, equals, hashCode, parallelStream, removeAll, removeIf, retainAll, stream

从接口继承的方法 java.lang.Iterable

forEach

从类继承的方法 java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

从接口继承的方法 java.util.Queue

element, remove

构造器详细资料

ConcurrentLinkedQueue

public ConcurrentLinkedQueue()

Creates a ConcurrentLinkedQueue that is initially empty.

ConcurrentLinkedQueue

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.

参数:

c - the collection of elements to initially contain

抛出:

NullPointerException - if the specified collection or any of its elements are null

方法详细资料

add

public boolean add(E e)

Inserts the specified element at the tail of this queue. As the queue is unbounded, this method will never throw IllegalStateException or return false.

指定者:

add 在接口中 Collection<E>

指定者:

add 在接口中 Queue<E>

覆盖:

add 在类中 AbstractQueue<E>

参数:

e - the element to add

返回:

true (as specified by Collection#add)

抛出:

NullPointerException - if the specified element is null

offer

public boolean offer(E e)

Inserts the specified element at the tail of this queue. As the queue is unbounded, this method will never return false.

指定者:

offer 在接口中 Queue<E>

参数:

e - the element to add

返回:

true (as specified by Queue#offer)

抛出:

NullPointerException - if the specified element is null

poll

public E poll()

从接口复制的说明: Queue

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

指定者:

poll 在接口中 Queue<E>

返回:

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

peek

public E peek()

从接口复制的说明: Queue

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

指定者:

peek 在接口中 Queue<E>

返回:

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

isEmpty

public boolean isEmpty()

Returns true if this queue contains no elements.

指定者:

isEmpty 在接口中 Collection<E>

覆盖:

isEmpty 在类中 AbstractCollection<E>

返回:

true if this queue contains no elements

size

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. Additionally, if elements are added or removed during execution of this method, the returned result may be inaccurate. Thus, this method is typically not very useful in concurrent applications.

指定者:

size 在接口中 Collection<E>

指定者:

size 在类中 AbstractCollection<E>

返回:

the number of elements in this queue

contains

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).

指定者:

contains 在接口中 Collection<E>

覆盖:

contains 在类中 AbstractCollection<E>

参数:

o - object to be checked for containment in this queue

返回:

true if this queue contains the specified element

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).

指定者:

remove 在接口中 Collection<E>

覆盖:

remove 在类中 AbstractCollection<E>

参数:

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

返回:

true if this queue changed as a result of the call

addAll

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

Appends all of the elements in the specified collection to the end of this queue, in the order that they are returned by the specified collection's iterator. Attempts to addAll of a queue to itself result in IllegalArgumentException.

指定者:

addAll 在接口中 Collection<E>

覆盖:

addAll 在类中 AbstractQueue<E>

参数:

c - the elements to be inserted into this queue

返回:

true if this queue changed as a result of the call

抛出:

NullPointerException - if the specified collection or any of its elements are null

IllegalArgumentException - if the collection is this queue

另请参阅:

AbstractQueue.add(Object)

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.

指定者:

toArray 在接口中 Collection<E>

覆盖:

toArray 在类中 AbstractCollection<E>

返回:

an array containing all of the elements in this queue

toArray

public <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. 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().

指定者:

toArray 在接口中 Collection<E>

覆盖:

toArray 在类中 AbstractCollection<E>

类型参数:

T - the runtime type of the array to contain the collection

参数:

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

返回:

an array containing all of the elements in this queue

抛出:

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

iterator

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.

指定者:

iterator 在接口中 Collection<E>

指定者:

iterator 在接口中 Iterable<E>

指定者:

iterator 在类中 AbstractCollection<E>

返回:

an iterator over the elements in this queue in proper sequence

spliterator

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.

指定者:

spliterator 在接口中 Collection<E>

指定者:

spliterator 在接口中 Iterable<E>

返回:

a Spliterator over the elements in this queue

从以下版本开始:

1.8