E
- the type of elements held in this collectionpublic class ConcurrentLinkedDeque<E>
extends java.util.AbstractCollection<E>
implements java.util.Deque<E>, java.io.Serializable
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 are weakly consistent, returning elements
reflecting the state of the deque at some point at or since the
creation of the iterator. They do not throw ConcurrentModificationException
, and may proceed concurrently with
other operations.
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.
This class is a member of the Java Collections Framework.
Constructor and Description |
---|
ConcurrentLinkedDeque()
Constructs an empty deque.
|
ConcurrentLinkedDeque(java.util.Collection<? extends E> c)
Constructs a deque 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 deque.
|
boolean |
addAll(java.util.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(java.lang.Object o)
Returns
true if this deque contains at least one
element e such that o.equals(e) . |
java.util.Iterator<E> |
descendingIterator()
Returns an iterator over the elements in this deque in reverse
sequential order.
|
E |
element() |
E |
getFirst() |
E |
getLast() |
boolean |
isEmpty()
Returns
true if this collection contains no elements. |
java.util.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() |
E |
peekFirst() |
E |
peekLast() |
E |
poll() |
E |
pollFirst() |
E |
pollLast() |
E |
pop() |
void |
push(E e) |
E |
remove() |
boolean |
remove(java.lang.Object o)
Removes the first element
e such that
o.equals(e) , if such an element exists in this deque. |
E |
removeFirst() |
boolean |
removeFirstOccurrence(java.lang.Object o)
Removes the first element
e such that
o.equals(e) , if such an element exists in this deque. |
E |
removeLast() |
boolean |
removeLastOccurrence(java.lang.Object o)
Removes the last element
e such that
o.equals(e) , if such an element exists in this deque. |
int |
size()
Returns the number of elements in this deque.
|
java.lang.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.
|
containsAll, removeAll, retainAll, toString
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
public ConcurrentLinkedDeque()
public ConcurrentLinkedDeque(java.util.Collection<? extends E> c)
c
- the collection of elements to initially containjava.lang.NullPointerException
- if the specified collection or any
of its elements are nullpublic void addFirst(E e)
IllegalStateException
.addFirst
in interface java.util.Deque<E>
java.lang.NullPointerException
- if the specified element is nullpublic void addLast(E e)
IllegalStateException
.
This method is equivalent to add(E)
.
addLast
in interface java.util.Deque<E>
java.lang.NullPointerException
- if the specified element is nullpublic boolean offerFirst(E e)
false
.offerFirst
in interface java.util.Deque<E>
true
(as specified by Deque.offerFirst(E)
)java.lang.NullPointerException
- if the specified element is nullpublic boolean offerLast(E e)
false
.
This method is equivalent to add(E)
.
offerLast
in interface java.util.Deque<E>
true
(as specified by Deque.offerLast(E)
)java.lang.NullPointerException
- if the specified element is nullpublic E getFirst()
getFirst
in interface java.util.Deque<E>
java.util.NoSuchElementException
public E getLast()
getLast
in interface java.util.Deque<E>
java.util.NoSuchElementException
public E removeFirst()
removeFirst
in interface java.util.Deque<E>
java.util.NoSuchElementException
public E removeLast()
removeLast
in interface java.util.Deque<E>
java.util.NoSuchElementException
public boolean offer(E e)
false
.public boolean add(E e)
IllegalStateException
or return false
.add
in interface java.util.Collection<E>
add
in interface java.util.Deque<E>
add
in interface java.util.Queue<E>
add
in class java.util.AbstractCollection<E>
true
(as specified by Collection.add(E)
)java.lang.NullPointerException
- if the specified element is nullpublic E poll()
public E remove()
public E peek()
public E element()
public boolean removeFirstOccurrence(java.lang.Object o)
e
such that
o.equals(e)
, if such an element exists in this deque.
If the deque does not contain the element, it is unchanged.removeFirstOccurrence
in interface java.util.Deque<E>
o
- element to be removed from this deque, if presenttrue
if the deque contained the specified elementjava.lang.NullPointerException
- if the specified element is nullpublic boolean removeLastOccurrence(java.lang.Object o)
e
such that
o.equals(e)
, if such an element exists in this deque.
If the deque does not contain the element, it is unchanged.removeLastOccurrence
in interface java.util.Deque<E>
o
- element to be removed from this deque, if presenttrue
if the deque contained the specified elementjava.lang.NullPointerException
- if the specified element is nullpublic boolean contains(java.lang.Object o)
true
if this deque contains at least one
element e
such that o.equals(e)
.contains
in interface java.util.Collection<E>
contains
in interface java.util.Deque<E>
contains
in class java.util.AbstractCollection<E>
o
- element whose presence in this deque is to be testedtrue
if this deque contains the specified elementpublic boolean isEmpty()
true
if this collection contains no elements.public int size()
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.
public boolean remove(java.lang.Object o)
e
such that
o.equals(e)
, if such an element exists in this deque.
If the deque does not contain the element, it is unchanged.remove
in interface java.util.Collection<E>
remove
in interface java.util.Deque<E>
remove
in class java.util.AbstractCollection<E>
o
- element to be removed from this deque, if presenttrue
if the deque contained the specified elementjava.lang.NullPointerException
- if the specified element is nullpublic boolean addAll(java.util.Collection<? extends E> c)
addAll
of a deque to
itself result in IllegalArgumentException
.addAll
in interface java.util.Collection<E>
addAll
in class java.util.AbstractCollection<E>
c
- the elements to be inserted into this dequetrue
if this deque changed as a result of the calljava.lang.NullPointerException
- if the specified collection or any
of its elements are nulljava.lang.IllegalArgumentException
- if the collection is this dequepublic void clear()
public java.lang.Object[] toArray()
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.
public <T> T[] toArray(T[] a)
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()
.toArray
in interface java.util.Collection<E>
toArray
in class java.util.AbstractCollection<E>
a
- 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 purposejava.lang.ArrayStoreException
- if the runtime type of the specified array
is not a supertype of the runtime type of every element in
this dequejava.lang.NullPointerException
- if the specified array is nullpublic java.util.Iterator<E> iterator()
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.
iterator
in interface java.lang.Iterable<E>
iterator
in interface java.util.Collection<E>
iterator
in interface java.util.Deque<E>
iterator
in class java.util.AbstractCollection<E>
public java.util.Iterator<E> descendingIterator()
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.
descendingIterator
in interface java.util.Deque<E>