public class ConcurrentLinkedQueue extends AbstractQueue implements Queue, java.io.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(java.util.Collection 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(java.lang.Object e)
Inserts the specified element at the tail of this queue.
|
boolean |
contains(java.lang.Object o)
Returns true if this queue contains the specified element.
|
boolean |
isEmpty()
Returns true if this queue contains no elements.
|
java.util.Iterator |
iterator()
Returns an iterator over the elements in this queue in proper sequence.
|
boolean |
offer(java.lang.Object e)
Inserts the specified element at the tail of this queue.
|
java.lang.Object |
peek()
Retrieves, but does not remove, the head of this queue,
or returns null if this queue is empty.
|
java.lang.Object |
poll()
Retrieves and removes the head of this queue,
or returns null if this queue is empty.
|
boolean |
remove(java.lang.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.
|
addAll, clear, element, remove
toArray, toArray
containsAll, removeAll, retainAll, toString
public ConcurrentLinkedQueue()
public ConcurrentLinkedQueue(java.util.Collection c)
c
- the collection of elements to initially containjava.lang.NullPointerException
- if the specified collection or any
of its elements are nullpublic boolean add(java.lang.Object e)
add
in interface Queue
add
in interface java.util.Collection
add
in class AbstractQueue
e
- the element to addCollection.add(java.lang.Object)
)java.lang.NullPointerException
- if the specified element is nullpublic boolean offer(java.lang.Object e)
offer
in interface Queue
e
- the element to addQueue.offer(java.lang.Object)
)java.lang.NullPointerException
- if the specified element is nullpublic java.lang.Object poll()
Queue
public java.lang.Object peek()
Queue
public boolean isEmpty()
isEmpty
in interface java.util.Collection
isEmpty
in class java.util.AbstractCollection
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 java.util.Collection
size
in class java.util.AbstractCollection
public boolean contains(java.lang.Object o)
contains
in interface java.util.Collection
contains
in class java.util.AbstractCollection
o
- object to be checked for containment in this queuepublic boolean remove(java.lang.Object o)
remove
in interface java.util.Collection
remove
in class java.util.AbstractCollection
o
- element to be removed from this queue, if presentpublic java.util.Iterator 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 java.lang.Iterable
iterator
in interface java.util.Collection
iterator
in class java.util.AbstractCollection