public class java.util.concurrent
ConcurrentLinkedQueue<E>


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Java SE 6
  
Extends: AbstractCollection > AbstractQueue
Implements: Queue, Serializable
Details
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 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.
since1.5
Ethe type of elements held in this collection


Constructors
public ConcurrentLinkedQueue()
Creates a ConcurrentLinkedQueue that is initially empty.
public ConcurrentLinkedQueue(Collection c) Details
Creates a ConcurrentLinkedQueue initially containing the elements of the given collection, added in traversal order of the collection's iterator.
cthe collection of elements to initially contain
ThrowsNullPointerException: if the specified collection or any of its elements are null

Methods
public boolean add(Object e) Details
Inserts the specified element at the tail of this queue.
returntrue (as specified by Collection#add)
ThrowsNullPointerException: als het gespecifieerde element null is
public boolean contains(Object o) Details
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).
oobject to be checked for containment in this queue
returntrue if this queue contains the specified element
public Iterator iterator() Details
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.
returnan iterator over the elements in this queue in proper sequence
public boolean offer(Object e) Details
Inserts the specified element at the tail of this queue.
returntrue (as specified by Queue#offer)
ThrowsNullPointerException: als het gespecifieerde element null is
public Object peek()
public Object poll()
public boolean remove(Object o) Details
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).
oelement to be removed from this queue, if present
returntrue if this queue changed as a result of the call
public int size() Details
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.
returnthe number of elements in this queue

public Object[] toArray() Details
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.
returnan array containing all of the elements in this queue

public Object[]<T> toArray(Object[] a) Details
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().
athe 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
returnan array containing all of the elements in this queue
ThrowsArrayStoreException: if the runtime type of the specified array is not a supertype of the runtime type of every element in this queue
ThrowsNullPointerException: if the specified array is null

Properties
public boolean isEmpty() Details
Returns true if this queue contains no elements.
returntrue if this queue contains no elements
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Java SE 6
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