public
class
ConcurrentLinkedDeque
extends AbstractCollection<E>
implements
Deque<E>,
Serializable
| java.lang.Object | ||
| ↳ | java.util.AbstractCollection<E> | |
| ↳ | java.util.concurrent.ConcurrentLinkedDeque<E> | |
An unbounded concurrent deque based on linked nodes.
Concurrent insertion, removal, and access operations execute safely
across multiple threads.
A ConcurrentLinkedDeque 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.
Iterators and spliterators are weakly consistent.
Beware that, unlike in most collections, the size method
is NOT a constant-time operation. Because of the
asynchronous nature of these deques, 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 Deque and Iterator interfaces.
Memory consistency effects: As with other concurrent collections,
actions in a thread prior to placing an object into a
ConcurrentLinkedDeque
happen-before
actions subsequent to the access or removal of that element from
the ConcurrentLinkedDeque in another thread.
Public constructors | |
|---|---|
ConcurrentLinkedDeque()
Constructs an empty deque. |
|
ConcurrentLinkedDeque(Collection<? extends E> c)
Constructs a deque initially containing the elements of the given collection, added in traversal order of the collection's iterator. |
|
Public methods | |
|---|---|
boolean
|
add(E e)
Inserts the specified element at the tail of this deque. |
boolean
|
addAll(Collection<? extends E> c)
Appends all of the elements in the specified collection to the end of this deque, in the order that they are returned by the specified collection's iterator. |
void
|
addFirst(E e)
Inserts the specified element at the front of this deque. |
void
|
addLast(E e)
Inserts the specified element at the end of this deque. |
void
|
clear()
Removes all of the elements from this deque. |
boolean
|
contains(Object o)
Returns |
Iterator<E>
|
descendingIterator()
Returns an iterator over the elements in this deque in reverse sequential order. |
E
|
element()
Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque). |
E
|
getFirst()
Retrieves, but does not remove, the first element of this deque. |
E
|
getLast()
Retrieves, but does not remove, the last element of this deque. |
boolean
|
isEmpty()
Returns |
Iterator<E>
|
iterator()
Returns an iterator over the elements in this deque in proper sequence. |
boolean
|
offer(E e)
Inserts the specified element at the tail of this deque. |
boolean
|
offerFirst(E e)
Inserts the specified element at the front of this deque. |
boolean
|
offerLast(E e)
Inserts the specified element at the end of this deque. |
E
|
peek()
Retrieves, but does not remove, the head of the queue represented by
this deque (in other words, the first element of this deque), or
returns |
E
|
peekFirst()
Retrieves, but does not remove, the first element of this deque,
or returns |
E
|
peekLast()
Retrieves, but does not remove, the last element of this deque,
or returns |
E
|
poll()
Retrieves and removes the head of the queue represented by this deque
(in other words, the first element of this deque), or returns
|
E
|
pollFirst()
Retrieves and removes the first element of this deque,
or returns |
E
|
pollLast()
Retrieves and removes the last element of this deque,
or returns |
E
|
pop()
Pops an element from the stack represented by this deque. |
void
|
push(E e)
Pushes an element onto the stack represented by this deque (in other
words, at the head of this deque) if it is possible to do so
immediately without violating capacity restrictions, throwing an
|
E
|
remove()
Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque). |
boolean
|
remove(Object o)
Removes the first occurrence of the specified element from this deque. |
E
|
removeFirst()
Retrieves and removes the first element of this deque. |
boolean
|
removeFirstOccurrence(Object o)
Removes the first occurrence of the specified element from this deque. |
E
|
removeLast()
Retrieves and removes the last element of this deque. |
boolean
|
removeLastOccurrence(Object o)
Removes the last occurrence of the specified element from this deque. |
int
|
size()
Returns the number of elements in this deque. |
Spliterator<E>
|
spliterator()
Returns a |
Object[]
|
toArray()
Returns an array containing all of the elements in this deque, in proper sequence (from first to last element). |
<T>
T[]
|
toArray(T[] a)
Returns an array containing all of the elements in this deque, in proper sequence (from first to last element); the runtime type of the returned array is that of the specified array. |
String
|
toString()
Returns a string representation of this collection. |
Inherited methods | |
|---|---|
 From
class
java.util.AbstractCollection
| |
From
class
java.lang.Object
| |
From
interface
java.util.Collection
| |
From
interface
java.util.Deque
| |
From
interface
java.lang.Iterable
| |
From
interface
java.util.Queue
| |
ConcurrentLinkedDeque (Collection<? extends E> c)
Constructs a deque initially containing the elements of the given collection, added in traversal order of the collection's iterator.
| Parameters | |
|---|---|
c |
Collection:
the collection of elements to initially contain |
| Throws | |
|---|---|
NullPointerException |
if the specified collection or any of its elements are null |
boolean add (E e)
Inserts the specified element at the tail of this deque.
As the deque is unbounded, this method will never throw
IllegalStateException or return false.
| Parameters | |
|---|---|
e |
E:
element whose presence in this collection is to be ensured |
| Returns | |
|---|---|
boolean |
true (as specified by add(E)) |
| Throws | |
|---|---|
NullPointerException |
if the specified element is null |
boolean addAll (Collection<? extends E> c)
Appends all of the elements in the specified collection to the end of
this deque, in the order that they are returned by the specified
collection's iterator. Attempts to addAll of a deque to
itself result in IllegalArgumentException.
| Parameters | |
|---|---|
c |
Collection:
the elements to be inserted into this deque |
| Returns | |
|---|---|
boolean |
true if this deque changed as a result of the call |
| Throws | |
|---|---|
NullPointerException |
if the specified collection or any of its elements are null |
IllegalArgumentException |
if the collection is this deque |
void addFirst (E e)
Inserts the specified element at the front of this deque.
As the deque is unbounded, this method will never throw
IllegalStateException.
| Parameters | |
|---|---|
e |
E:
the element to add |
| Throws | |
|---|---|
NullPointerException |
if the specified element is null |
void addLast (E e)
Inserts the specified element at the end of this deque.
As the deque is unbounded, this method will never throw
IllegalStateException.
This method is equivalent to add(E).
| Parameters | |
|---|---|
e |
E:
the element to add |
| Throws | |
|---|---|
NullPointerException |
if the specified element is null |
boolean contains (Object o)
Returns true if this deque contains the specified element.
More formally, returns true if and only if this deque contains
at least one element e such that o.equals(e).
| Parameters | |
|---|---|
o |
Object:
element whose presence in this deque is to be tested |
| Returns | |
|---|---|
boolean |
true if this deque contains the specified element
|
Iterator<E> descendingIterator ()
Returns an iterator over the elements in this deque in reverse sequential order. The elements will be returned in order from last (tail) to first (head).
The returned iterator is weakly consistent.
| Returns | |
|---|---|
Iterator<E> |
an iterator over the elements in this deque in reverse order |
E element ()
Retrieves, but does not remove, the head of the queue represented by
this deque (in other words, the first element of this deque).
This method differs from peek only in that it throws an
exception if this deque is empty.
This method is equivalent to getFirst().
| Returns | |
|---|---|
E |
the head of the queue represented by this deque |
| Throws | |
|---|---|
NoSuchElementException |
|
E getFirst ()
Retrieves, but does not remove, the first element of this deque.
This method differs from peekFirst only in that it
throws an exception if this deque is empty.
| Returns | |
|---|---|
E |
the head of this deque |
| Throws | |
|---|---|
NoSuchElementException |
|
E getLast ()
Retrieves, but does not remove, the last element of this deque.
This method differs from peekLast only in that it
throws an exception if this deque is empty.
| Returns | |
|---|---|
E |
the tail of this deque |
| Throws | |
|---|---|
NoSuchElementException |
|
boolean isEmpty ()
Returns true if this collection contains no elements.
| Returns | |
|---|---|
boolean |
true if this collection contains no elements
|
Iterator<E> iterator ()
Returns an iterator over the elements in this deque in proper sequence. The elements will be returned in order from first (head) to last (tail).
The returned iterator is weakly consistent.
| Returns | |
|---|---|
Iterator<E> |
an iterator over the elements in this deque in proper sequence |
boolean offer (E e)
Inserts the specified element at the tail of this deque.
As the deque is unbounded, this method will never return false.
| Parameters | |
|---|---|
e |
E:
the element to add |
| Returns | |
|---|---|
boolean |
true (as specified by offer(E)) |
| Throws | |
|---|---|
NullPointerException |
if the specified element is null |
boolean offerFirst (E e)
Inserts the specified element at the front of this deque.
As the deque is unbounded, this method will never return false.
| Parameters | |
|---|---|
e |
E:
the element to add |
| Returns | |
|---|---|
boolean |
true (as specified by offerFirst(E)) |
| Throws | |
|---|---|
NullPointerException |
if the specified element is null |
boolean offerLast (E e)
Inserts the specified element at the end of this deque.
As the deque is unbounded, this method will never return false.
This method is equivalent to add(E).
| Parameters | |
|---|---|
e |
E:
the element to add |
| Returns | |
|---|---|
boolean |
true (as specified by offerLast(E)) |
| Throws | |
|---|---|
NullPointerException |
if the specified element is null |
E peek ()
Retrieves, but does not remove, the head of the queue represented by
this deque (in other words, the first element of this deque), or
returns null if this deque is empty.
This method is equivalent to peekFirst().
| Returns | |
|---|---|
E |
the head of the queue represented by this deque, or
null if this deque is empty
|
E peekFirst ()
Retrieves, but does not remove, the first element of this deque,
or returns null if this deque is empty.
| Returns | |
|---|---|
E |
the head of this deque, or null if this deque is empty
|
E peekLast ()
Retrieves, but does not remove, the last element of this deque,
or returns null if this deque is empty.
| Returns | |
|---|---|
E |
the tail of this deque, or null if this deque is empty
|
E poll ()
Retrieves and removes the head of the queue represented by this deque
(in other words, the first element of this deque), or returns
null if this deque is empty.
This method is equivalent to pollFirst().
| Returns | |
|---|---|
E |
the first element of this deque, or null if
this deque is empty
|
E pollFirst ()
Retrieves and removes the first element of this deque,
or returns null if this deque is empty.
| Returns | |
|---|---|
E |
the head of this deque, or null if this deque is empty
|
E pollLast ()
Retrieves and removes the last element of this deque,
or returns null if this deque is empty.
| Returns | |
|---|---|
E |
the tail of this deque, or null if this deque is empty
|
E pop ()
Pops an element from the stack represented by this deque. In other words, removes and returns the first element of this deque.
This method is equivalent to removeFirst().
| Returns | |
|---|---|
E |
the element at the front of this deque (which is the top of the stack represented by this deque) |
| Throws | |
|---|---|
NoSuchElementException |
|
void push (E e)
Pushes an element onto the stack represented by this deque (in other
words, at the head of this deque) if it is possible to do so
immediately without violating capacity restrictions, throwing an
IllegalStateException if no space is currently available.
This method is equivalent to addFirst(E).
| Parameters | |
|---|---|
e |
E:
the element to push |
| Throws | |
|---|---|
NullPointerException |
|
E remove ()
Retrieves and removes the head of the queue represented by this deque
(in other words, the first element of this deque).
This method differs from poll only in that it throws an
exception if this deque is empty.
This method is equivalent to removeFirst().
| Returns | |
|---|---|
E |
the head of the queue represented by this deque |
| Throws | |
|---|---|
NoSuchElementException |
|
boolean remove (Object o)
Removes the first occurrence of the specified element from this deque.
If the deque does not contain the element, it is unchanged.
More formally, removes the first element e such that
o.equals(e) (if such an element exists).
Returns true if this deque contained the specified element
(or equivalently, if this deque changed as a result of the call).
This method is equivalent to removeFirstOccurrence(Object).
| Parameters | |
|---|---|
o |
Object:
element to be removed from this deque, if present |
| Returns | |
|---|---|
boolean |
true if the deque contained the specified element |
| Throws | |
|---|---|
NullPointerException |
if the specified element is null |
E removeFirst ()
Retrieves and removes the first element of this deque. This method
differs from pollFirst only in that it throws an
exception if this deque is empty.
| Returns | |
|---|---|
E |
the head of this deque |
| Throws | |
|---|---|
NoSuchElementException |
|
boolean removeFirstOccurrence (Object o)
Removes the first occurrence of the specified element from this deque.
If the deque does not contain the element, it is unchanged.
More formally, removes the first element e such that
o.equals(e) (if such an element exists).
Returns true if this deque contained the specified element
(or equivalently, if this deque changed as a result of the call).
| Parameters | |
|---|---|
o |
Object:
element to be removed from this deque, if present |
| Returns | |
|---|---|
boolean |
true if the deque contained the specified element |
| Throws | |
|---|---|
NullPointerException |
if the specified element is null |
E removeLast ()
Retrieves and removes the last element of this deque. This method
differs from pollLast only in that it throws an
exception if this deque is empty.
| Returns | |
|---|---|
E |
the tail of this deque |
| Throws | |
|---|---|
NoSuchElementException |
|
boolean removeLastOccurrence (Object o)
Removes the last occurrence of the specified element from this deque.
If the deque does not contain the element, it is unchanged.
More formally, removes the last element e such that
o.equals(e) (if such an element exists).
Returns true if this deque contained the specified element
(or equivalently, if this deque changed as a result of the call).
| Parameters | |
|---|---|
o |
Object:
element to be removed from this deque, if present |
| Returns | |
|---|---|
boolean |
true if the deque contained the specified element |
| Throws | |
|---|---|
NullPointerException |
if the specified element is null |
int size ()
Returns the number of elements in this deque. If this deque
contains more than Integer.MAX_VALUE elements, it
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 deques, determining the current number of elements requires traversing them all to count them. Additionally, it is possible for the size to change during execution of this method, in which case the returned result will be inaccurate. Thus, this method is typically not very useful in concurrent applications.
| Returns | |
|---|---|
int |
the number of elements in this deque |
Spliterator<E> spliterator ()
Returns a Spliterator over the elements in this deque.
The returned spliterator is weakly consistent.
The Spliterator reports CONCURRENT,
ORDERED, and NONNULL.
Developers
Spliterator implements trySplit to permit limited
parallelism.| Returns | |
|---|---|
Spliterator<E> |
a Spliterator over the elements in this deque |
Object[] toArray ()
Returns an array containing all of the elements in this deque, in proper sequence (from first to last element).
The returned array will be "safe" in that no references to it are maintained by this deque. (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.
| Returns | |
|---|---|
Object[] |
an array containing all of the elements in this deque |
T[] toArray (T[] a)
Returns an array containing all of the elements in this deque, in proper sequence (from first to last element); the runtime type of the returned array is that of the specified array. If the deque 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 deque.
If this deque fits in the specified array with room to spare
(i.e., the array has more elements than this deque), the element in
the array immediately following the end of the deque 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 deque known to contain only strings.
The following code can be used to dump the deque 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().
| Parameters | |
|---|---|
a |
T:
the array into which the elements of the deque are to
be stored, if it is big enough; otherwise, a new array of the
same runtime type is allocated for this purpose |
| Returns | |
|---|---|
T[] |
an array containing all of the elements in this deque |
| Throws | |
|---|---|
ArrayStoreException |
if the runtime type of the specified array is not a supertype of the runtime type of every element in this deque |
NullPointerException |
if the specified array is null |
String toString ()
Returns a string representation of this collection. The string
representation consists of a list of the collection's elements in the
order they are returned by its iterator, enclosed in square brackets
("[]"). Adjacent elements are separated by the characters
", " (comma and space). Elements are converted to strings as
by valueOf(Object).
| Returns | |
|---|---|
String |
a string representation of this collection |