java.util.concurrent
E - the type of elements held in this collectionpublic class ConcurrentLinkedQueue<E> extends AbstractQueue<E> implements Queue<E>, Serializable
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 and its iterator implement all of the
optional methods of the Collection 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.
| Constructor and Description |
|---|
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.
|
| Modifier and Type | Method and Description |
|---|---|
boolean |
add(E e)
Inserts the specified element at the tail of this queue.
|
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.
|
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.
|
addAll, clear, element, removecontainsAll, removeAll, retainAll, toStringclone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, waitaddAll, clear, containsAll, equals, hashCode, removeAll, retainAllpublic ConcurrentLinkedQueue()
public ConcurrentLinkedQueue(Collection<? extends E> c)
c - the collection of elements to initially containNullPointerException - if the specified collection or any
of its elements are nullpublic boolean add(E e)
add in interface Collection<E>add in interface Queue<E>add in class AbstractQueue<E>e - the element to addCollection.add(E))NullPointerException - if the specified element is nullpublic boolean offer(E e)
offer in interface Queue<E>e - the element to addQueue.offer(E))NullPointerException - if the specified element is nullpublic E poll()
Queuepublic E peek()
Queuepublic boolean isEmpty()
isEmpty in interface Collection<E>isEmpty in class AbstractCollection<E>public int size()
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.
size in interface Collection<E>size in class AbstractCollection<E>public boolean contains(Object o)
contains in interface Collection<E>contains in class AbstractCollection<E>o - object to be checked for containment in this queuepublic boolean remove(Object o)
remove in interface Collection<E>remove in class AbstractCollection<E>o - element to be removed from this queue, if presentpublic Object[] toArray()
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.
toArray in interface Collection<E>toArray in class AbstractCollection<E>public <T> T[] toArray(T[] a)
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().toArray in interface Collection<E>toArray in class AbstractCollection<E>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 purposeArrayStoreException - if the runtime type of the specified array
is not a supertype of the runtime type of every element in
this queueNullPointerException - if the specified array is nullpublic Iterator<E> iterator()
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.iterator in interface Iterable<E>iterator in interface Collection<E>iterator in class AbstractCollection<E> Submit a bug or feature Copyright © 1993, 2017, Oracle and/or its affiliates. All rights reserved.
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.