java.util.concurrent
Class ConcurrentLinkedQueue<E>

java.lang.Object sample code for java.lang.Object definition code for java.lang.Object 
  extended by java.util.AbstractCollection sample code for java.util.AbstractCollection definition code for java.util.AbstractCollection <E>
      extended by java.util.AbstractQueue sample code for java.util.AbstractQueue definition code for java.util.AbstractQueue <E>
          extended by java.util.concurrent.ConcurrentLinkedQueue<E>
Type Parameters:
E - the type of elements held in this collection
All Implemented Interfaces:
Serializable sample code for java.io.Serializable definition code for java.io.Serializable , Iterable sample code for java.lang.Iterable definition code for java.lang.Iterable <E>, Collection sample code for java.util.Collection definition code for java.util.Collection <E>, Queue sample code for java.util.Queue definition code for java.util.Queue <E>

public class ConcurrentLinkedQueue<E>
extends AbstractQueue sample code for java.util.AbstractQueue definition code for java.util.AbstractQueue <E>
implements Queue sample code for java.util.Queue definition code for java.util.Queue <E>, Serializable sample code for java.io.Serializable definition code for java.io.Serializable

An unbounded thread-safe queue sample code for java.util.Queue definition code for java.util.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 sample code for java.util.Collection definition code for java.util.Collection and Iterator sample code for java.util.Iterator definition code for java.util.Iterator interfaces.

This class is a member of the Java Collections Framework.

Since:
1.5
See Also:
Serialized Form

Constructor Summary
ConcurrentLinkedQueue sample code for java.util.concurrent.ConcurrentLinkedQueue.ConcurrentLinkedQueue() definition code for java.util.concurrent.ConcurrentLinkedQueue.ConcurrentLinkedQueue() ()
          Creates a ConcurrentLinkedQueue that is initially empty.
ConcurrentLinkedQueue sample code for java.util.concurrent.ConcurrentLinkedQueue.ConcurrentLinkedQueue(java.util.Collection) definition code for java.util.concurrent.ConcurrentLinkedQueue.ConcurrentLinkedQueue(java.util.Collection) (Collection sample code for java.util.Collection definition code for java.util.Collection <? extends E> c)
          Creates a ConcurrentLinkedQueue initially containing the elements of the given collection, added in traversal order of the collection's iterator.
 
Method Summary
 boolean add sample code for java.util.concurrent.ConcurrentLinkedQueue.add(E) definition code for java.util.concurrent.ConcurrentLinkedQueue.add(E) (E o)
          Adds the specified element to the tail of this queue.
 boolean contains sample code for java.util.concurrent.ConcurrentLinkedQueue.contains(java.lang.Object) definition code for java.util.concurrent.ConcurrentLinkedQueue.contains(java.lang.Object) (Object sample code for java.lang.Object definition code for java.lang.Object  o)
          Returns true if this collection contains the specified element.
 boolean isEmpty sample code for java.util.concurrent.ConcurrentLinkedQueue.isEmpty() definition code for java.util.concurrent.ConcurrentLinkedQueue.isEmpty() ()
          Returns true if this collection contains no elements.
 Iterator sample code for java.util.Iterator definition code for java.util.Iterator <E> iterator sample code for java.util.concurrent.ConcurrentLinkedQueue.iterator() definition code for java.util.concurrent.ConcurrentLinkedQueue.iterator() ()
          Returns an iterator over the elements in this queue in proper sequence.
 boolean offer sample code for java.util.concurrent.ConcurrentLinkedQueue.offer(E) definition code for java.util.concurrent.ConcurrentLinkedQueue.offer(E) (E o)
          Inserts the specified element to the tail of this queue.
 E peek sample code for java.util.concurrent.ConcurrentLinkedQueue.peek() definition code for java.util.concurrent.ConcurrentLinkedQueue.peek() ()
          Retrieves, but does not remove, the head of this queue, returning null if this queue is empty.
 E poll sample code for java.util.concurrent.ConcurrentLinkedQueue.poll() definition code for java.util.concurrent.ConcurrentLinkedQueue.poll() ()
          Retrieves and removes the head of this queue, or null if this queue is empty.
 boolean remove sample code for java.util.concurrent.ConcurrentLinkedQueue.remove(java.lang.Object) definition code for java.util.concurrent.ConcurrentLinkedQueue.remove(java.lang.Object) (Object sample code for java.lang.Object definition code for java.lang.Object  o)
          Removes a single instance of the specified element from this collection, if it is present (optional operation).
 int size sample code for java.util.concurrent.ConcurrentLinkedQueue.size() definition code for java.util.concurrent.ConcurrentLinkedQueue.size() ()
          Returns the number of elements in this queue.
 Object sample code for java.lang.Object definition code for java.lang.Object [] toArray sample code for java.util.concurrent.ConcurrentLinkedQueue.toArray() definition code for java.util.concurrent.ConcurrentLinkedQueue.toArray() ()
          Returns an array containing all of the elements in this collection.
<T> T[]
toArray sample code for java.util.concurrent.ConcurrentLinkedQueue.toArray(T[]) definition code for java.util.concurrent.ConcurrentLinkedQueue.toArray(T[]) (T[] a)
          Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array.
 
Methods inherited from class java.util.AbstractQueue sample code for java.util.AbstractQueue definition code for java.util.AbstractQueue
addAll sample code for java.util.AbstractQueue.addAll(java.util.Collection) definition code for java.util.AbstractQueue.addAll(java.util.Collection) , clear sample code for java.util.AbstractQueue.clear() definition code for java.util.AbstractQueue.clear() , element sample code for java.util.AbstractQueue.element() definition code for java.util.AbstractQueue.element() , remove sample code for java.util.AbstractQueue.remove() definition code for java.util.AbstractQueue.remove()
 
Methods inherited from class java.util.AbstractCollection sample code for java.util.AbstractCollection definition code for java.util.AbstractCollection
containsAll sample code for java.util.AbstractCollection.containsAll(java.util.Collection) definition code for java.util.AbstractCollection.containsAll(java.util.Collection) , removeAll sample code for java.util.AbstractCollection.removeAll(java.util.Collection) definition code for java.util.AbstractCollection.removeAll(java.util.Collection) , retainAll sample code for java.util.AbstractCollection.retainAll(java.util.Collection) definition code for java.util.AbstractCollection.retainAll(java.util.Collection) , toString sample code for java.util.AbstractCollection.toString() definition code for java.util.AbstractCollection.toString()
 
Methods inherited from class java.lang.Object sample code for java.lang.Object definition code for java.lang.Object
clone sample code for java.lang.Object.clone() definition code for java.lang.Object.clone() , equals sample code for java.lang.Object.equals(java.lang.Object) definition code for java.lang.Object.equals(java.lang.Object) , finalize sample code for java.lang.Object.finalize() definition code for java.lang.Object.finalize() , getClass sample code for java.lang.Object.getClass() definition code for java.lang.Object.getClass() , hashCode sample code for java.lang.Object.hashCode() definition code for java.lang.Object.hashCode() , notify sample code for java.lang.Object.notify() definition code for java.lang.Object.notify() , notifyAll sample code for java.lang.Object.notifyAll() definition code for java.lang.Object.notifyAll() , wait sample code for java.lang.Object.wait() definition code for java.lang.Object.wait() , wait sample code for java.lang.Object.wait(long) definition code for java.lang.Object.wait(long) , wait sample code for java.lang.Object.wait(long, int) definition code for java.lang.Object.wait(long, int)
 
Methods inherited from interface java.util.Queue sample code for java.util.Queue definition code for java.util.Queue
element sample code for java.util.Queue.element() definition code for java.util.Queue.element() , remove sample code for java.util.Queue.remove() definition code for java.util.Queue.remove()
 
Methods inherited from interface java.util.Collection sample code for java.util.Collection definition code for java.util.Collection
addAll sample code for java.util.Collection.addAll(java.util.Collection) definition code for java.util.Collection.addAll(java.util.Collection) , clear sample code for java.util.Collection.clear() definition code for java.util.Collection.clear() , containsAll sample code for java.util.Collection.containsAll(java.util.Collection) definition code for java.util.Collection.containsAll(java.util.Collection) , equals sample code for java.util.Collection.equals(java.lang.Object) definition code for java.util.Collection.equals(java.lang.Object) , hashCode sample code for java.util.Collection.hashCode() definition code for java.util.Collection.hashCode() , removeAll sample code for java.util.Collection.removeAll(java.util.Collection) definition code for java.util.Collection.removeAll(java.util.Collection) , retainAll sample code for java.util.Collection.retainAll(java.util.Collection) definition code for java.util.Collection.retainAll(java.util.Collection)
 

Constructor Detail

ConcurrentLinkedQueue sample code for java.util.concurrent.ConcurrentLinkedQueue() definition code for java.util.concurrent.ConcurrentLinkedQueue()

public ConcurrentLinkedQueue()
Creates a ConcurrentLinkedQueue that is initially empty.


ConcurrentLinkedQueue sample code for java.util.concurrent.ConcurrentLinkedQueue(java.util.Collection<? extends E>) definition code for java.util.concurrent.ConcurrentLinkedQueue(java.util.Collection<? extends E>)

public ConcurrentLinkedQueue(Collection sample code for java.util.Collection definition code for java.util.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 sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if c or any element within it is null
Method Detail

add sample code for java.util.concurrent.ConcurrentLinkedQueue.add(E) definition code for java.util.concurrent.ConcurrentLinkedQueue.add(E)

public boolean add(E o)
Adds the specified element to the tail of this queue.

Specified by:
add sample code for java.util.Collection.add(E) definition code for java.util.Collection.add(E) in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Overrides:
add sample code for java.util.AbstractQueue.add(E) definition code for java.util.AbstractQueue.add(E) in class AbstractQueue sample code for java.util.AbstractQueue definition code for java.util.AbstractQueue <E>
Parameters:
o - the element to add.
Returns:
true (as per the general contract of Collection.add).
Throws:
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the specified element is null

offer sample code for java.util.concurrent.ConcurrentLinkedQueue.offer(E) definition code for java.util.concurrent.ConcurrentLinkedQueue.offer(E)

public boolean offer(E o)
Inserts the specified element to the tail of this queue.

Specified by:
offer sample code for java.util.Queue.offer(E) definition code for java.util.Queue.offer(E) in interface Queue sample code for java.util.Queue definition code for java.util.Queue <E>
Parameters:
o - the element to add.
Returns:
true (as per the general contract of Queue.offer).
Throws:
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the specified element is null

poll sample code for java.util.concurrent.ConcurrentLinkedQueue.poll() definition code for java.util.concurrent.ConcurrentLinkedQueue.poll()

public E poll()
Description copied from interface: Queue sample code for java.util.Queue.poll() definition code for java.util.Queue.poll()
Retrieves and removes the head of this queue, or null if this queue is empty.

Specified by:
poll sample code for java.util.Queue.poll() definition code for java.util.Queue.poll() in interface Queue sample code for java.util.Queue definition code for java.util.Queue <E>
Returns:
the head of this queue, or null if this queue is empty.

peek sample code for java.util.concurrent.ConcurrentLinkedQueue.peek() definition code for java.util.concurrent.ConcurrentLinkedQueue.peek()

public E peek()
Description copied from interface: Queue sample code for java.util.Queue.peek() definition code for java.util.Queue.peek()
Retrieves, but does not remove, the head of this queue, returning null if this queue is empty.

Specified by:
peek sample code for java.util.Queue.peek() definition code for java.util.Queue.peek() in interface Queue sample code for java.util.Queue definition code for java.util.Queue <E>
Returns:
the head of this queue, or null if this queue is empty.

isEmpty sample code for java.util.concurrent.ConcurrentLinkedQueue.isEmpty() definition code for java.util.concurrent.ConcurrentLinkedQueue.isEmpty()

public boolean isEmpty()
Description copied from class: AbstractCollection sample code for java.util.AbstractCollection.isEmpty() definition code for java.util.AbstractCollection.isEmpty()
Returns true if this collection contains no elements.

This implementation returns size() == 0.

Specified by:
isEmpty sample code for java.util.Collection.isEmpty() definition code for java.util.Collection.isEmpty() in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Overrides:
isEmpty sample code for java.util.AbstractCollection.isEmpty() definition code for java.util.AbstractCollection.isEmpty() in class AbstractCollection sample code for java.util.AbstractCollection definition code for java.util.AbstractCollection <E>
Returns:
true if this collection contains no elements.

size sample code for java.util.concurrent.ConcurrentLinkedQueue.size() definition code for java.util.concurrent.ConcurrentLinkedQueue.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.

Specified by:
size sample code for java.util.Collection.size() definition code for java.util.Collection.size() in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Specified by:
size sample code for java.util.AbstractCollection.size() definition code for java.util.AbstractCollection.size() in class AbstractCollection sample code for java.util.AbstractCollection definition code for java.util.AbstractCollection <E>
Returns:
the number of elements in this queue.

contains sample code for java.util.concurrent.ConcurrentLinkedQueue.contains(java.lang.Object) definition code for java.util.concurrent.ConcurrentLinkedQueue.contains(java.lang.Object)

public boolean contains(Object sample code for java.lang.Object definition code for java.lang.Object  o)
Description copied from class: AbstractCollection sample code for java.util.AbstractCollection.contains(java.lang.Object) definition code for java.util.AbstractCollection.contains(java.lang.Object)
Returns true if this collection contains the specified element. More formally, returns true if and only if this collection contains at least one element e such that (o==null ? e==null : o.equals(e)).

This implementation iterates over the elements in the collection, checking each element in turn for equality with the specified element.

Specified by:
contains sample code for java.util.Collection.contains(java.lang.Object) definition code for java.util.Collection.contains(java.lang.Object) in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Overrides:
contains sample code for java.util.AbstractCollection.contains(java.lang.Object) definition code for java.util.AbstractCollection.contains(java.lang.Object) in class AbstractCollection sample code for java.util.AbstractCollection definition code for java.util.AbstractCollection <E>
Parameters:
o - object to be checked for containment in this collection.
Returns:
true if this collection contains the specified element.

remove sample code for java.util.concurrent.ConcurrentLinkedQueue.remove(java.lang.Object) definition code for java.util.concurrent.ConcurrentLinkedQueue.remove(java.lang.Object)

public boolean remove(Object sample code for java.lang.Object definition code for java.lang.Object  o)
Description copied from class: AbstractCollection sample code for java.util.AbstractCollection.remove(java.lang.Object) definition code for java.util.AbstractCollection.remove(java.lang.Object)
Removes a single instance of the specified element from this collection, if it is present (optional operation). More formally, removes an element e such that (o==null ? e==null : o.equals(e)), if the collection contains one or more such elements. Returns true if the collection contained the specified element (or equivalently, if the collection changed as a result of the call).

This implementation iterates over the collection looking for the specified element. If it finds the element, it removes the element from the collection using the iterator's remove method.

Note that this implementation throws an UnsupportedOperationException if the iterator returned by this collection's iterator method does not implement the remove method and this collection contains the specified object.

Specified by:
remove sample code for java.util.Collection.remove(java.lang.Object) definition code for java.util.Collection.remove(java.lang.Object) in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Overrides:
remove sample code for java.util.AbstractCollection.remove(java.lang.Object) definition code for java.util.AbstractCollection.remove(java.lang.Object) in class AbstractCollection sample code for java.util.AbstractCollection definition code for java.util.AbstractCollection <E>
Parameters:
o - element to be removed from this collection, if present.
Returns:
true if the collection contained the specified element.

toArray sample code for java.util.concurrent.ConcurrentLinkedQueue.toArray() definition code for java.util.concurrent.ConcurrentLinkedQueue.toArray()

public Object sample code for java.lang.Object definition code for java.lang.Object [] toArray()
Description copied from class: AbstractCollection sample code for java.util.AbstractCollection.toArray() definition code for java.util.AbstractCollection.toArray()
Returns an array containing all of the elements in this 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 the same order. The returned array will be "safe" in that no references to it are maintained by the collection. (In other words, this method must allocate a new array even if the collection is backed by an Array). The caller is thus free to modify the returned array.

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 sample code for java.util.Collection.toArray() definition code for java.util.Collection.toArray() in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Overrides:
toArray sample code for java.util.AbstractCollection.toArray() definition code for java.util.AbstractCollection.toArray() in class AbstractCollection sample code for java.util.AbstractCollection definition code for java.util.AbstractCollection <E>
Returns:
an array containing all of the elements in this collection.

toArray sample code for java.util.concurrent.ConcurrentLinkedQueue.<T>toArray(T[]) definition code for java.util.concurrent.ConcurrentLinkedQueue.<T>toArray(T[])

public <T> T[] toArray(T[] a)
Description copied from class: AbstractCollection sample code for java.util.AbstractCollection.toArray(T[]) definition code for java.util.AbstractCollection.toArray(T[])
Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array. If the 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 collection.

If the collection fits in the specified array with room to spare (i.e., the array has more elements than the collection), the element in the array immediately following the end of the 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.)

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.

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 null is stored in the first location after the end of the collection.

Specified by:
toArray sample code for java.util.Collection.toArray(T[]) definition code for java.util.Collection.toArray(T[]) in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Overrides:
toArray sample code for java.util.AbstractCollection.toArray(T[]) definition code for java.util.AbstractCollection.toArray(T[]) in class AbstractCollection sample code for java.util.AbstractCollection definition code for java.util.AbstractCollection <E>
Parameters:
a - the array into which the elements of the collection are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.
Returns:
an array containing the elements of the collection.

iterator sample code for java.util.concurrent.ConcurrentLinkedQueue.iterator() definition code for java.util.concurrent.ConcurrentLinkedQueue.iterator()

public Iterator sample code for java.util.Iterator definition code for java.util.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 sample code for java.util.ConcurrentModificationException definition code for java.util.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 sample code for java.lang.Iterable.iterator() definition code for java.lang.Iterable.iterator() in interface Iterable sample code for java.lang.Iterable definition code for java.lang.Iterable <E>
Specified by:
iterator sample code for java.util.Collection.iterator() definition code for java.util.Collection.iterator() in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Specified by:
iterator sample code for java.util.AbstractCollection.iterator() definition code for java.util.AbstractCollection.iterator() in class AbstractCollection sample code for java.util.AbstractCollection definition code for java.util.AbstractCollection <E>
Returns:
an iterator over the elements in this queue in proper sequence.