Class ConcurrentLinkedDeque<E>
- java.lang.Object
-
- java.util.AbstractCollection<E>
-
- java.util.concurrent.ConcurrentLinkedDeque<E>
- Type Parameters:
-
E
- the type of elements held in this deque
- All Implemented Interfaces:
-
Serializable
,Iterable<E>
,Collection<E>
,Deque<E>
,Queue<E>
public class ConcurrentLinkedDeque<E> extends AbstractCollection<E> implements Deque<E>, Serializable
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.
Bulk operations that add, remove, or examine multiple elements, such as addAll(java.util.Collection<? extends E>)
, removeIf(java.util.function.Predicate<? super E>)
or forEach(java.util.function.Consumer<? super E>)
, are not guaranteed to be performed atomically. For example, a forEach
traversal concurrent with an
addAll
operation might observe 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.
- Since:
- 1.7
- See Also:
- Serialized Form
Constructor Summary
Constructor | Description |
---|---|
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. |
Method Summary
Modifier and Type | Method | Description |
---|---|---|
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). |
void | forEach(Consumer<? super E> action) | Performs the given action for each element of the |
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 | 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. |
boolean | removeAll(Collection<?> c) | Removes all of this collection's elements that are also contained in the specified collection (optional operation). |
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. |
boolean | removeIf(Predicate<? super E> filter) | Removes all of the elements of this collection that satisfy the given predicate. |
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. |
boolean | retainAll(Collection<?> c) | Retains only the elements in this collection that are contained in the specified collection (optional operation). |
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. |
Methods declared in class java.util.AbstractCollection
containsAll, toString
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
Methods declared in interface java.util.Collection
containsAll, equals, hashCode, parallelStream, stream, toArray
Methods declared in interface java.util.Deque
peek, peekFirst, peekLast, poll, pollFirst, pollLast
Constructor Detail
ConcurrentLinkedDeque
public ConcurrentLinkedDeque()
Constructs an empty deque.
ConcurrentLinkedDeque
public 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
- the collection of elements to initially contain - Throws:
-
NullPointerException
- if the specified collection or any of its elements are null
Method Detail
addFirst
public 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
.
- Specified by:
-
addFirst
in interfaceDeque<E>
- Parameters:
-
e
- the element to add - Throws:
-
NullPointerException
- if the specified element is null
addLast
public 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)
.
- Specified by:
-
addLast
in interfaceDeque<E>
- Parameters:
-
e
- the element to add - Throws:
-
NullPointerException
- if the specified element is null
offerFirst
public 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
.
- Specified by:
-
offerFirst
in interfaceDeque<E>
- Parameters:
-
e
- the element to add - Returns:
-
true
(as specified byDeque.offerFirst(E)
) - Throws:
-
NullPointerException
- if the specified element is null
offerLast
public 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)
.
- Specified by:
-
offerLast
in interfaceDeque<E>
- Parameters:
-
e
- the element to add - Returns:
-
true
(as specified byDeque.offerLast(E)
) - Throws:
-
NullPointerException
- if the specified element is null
getFirst
public E getFirst()
Description copied from interface: Deque
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.
- Specified by:
-
getFirst
in interfaceDeque<E>
- Returns:
- the head of this deque
- Throws:
-
NoSuchElementException
- if this deque is empty
getLast
public E getLast()
Description copied from interface: Deque
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.
- Specified by:
-
getLast
in interfaceDeque<E>
- Returns:
- the tail of this deque
- Throws:
-
NoSuchElementException
- if this deque is empty
removeFirst
public E removeFirst()
Description copied from interface: Deque
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.
- Specified by:
-
removeFirst
in interfaceDeque<E>
- Returns:
- the head of this deque
- Throws:
-
NoSuchElementException
- if this deque is empty
removeLast
public E removeLast()
Description copied from interface: Deque
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.
- Specified by:
-
removeLast
in interfaceDeque<E>
- Returns:
- the tail of this deque
- Throws:
-
NoSuchElementException
- if this deque is empty
offer
public 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
.
- Specified by:
-
offer
in interfaceDeque<E>
- Specified by:
-
offer
in interfaceQueue<E>
- Parameters:
-
e
- the element to add - Returns:
-
true
(as specified byQueue.offer(E)
) - Throws:
-
NullPointerException
- if the specified element is null
add
public 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
.
- Specified by:
-
add
in interfaceCollection<E>
- Specified by:
-
add
in interfaceDeque<E>
- Specified by:
-
add
in interfaceQueue<E>
- Overrides:
-
add
in classAbstractCollection<E>
- Parameters:
-
e
- element whose presence in this collection is to be ensured - Returns:
-
true
(as specified byCollection.add(E)
) - Throws:
-
NullPointerException
- if the specified element is null
remove
public E remove()
Description copied from interface: Deque
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 Deque.removeFirst()
.
- Specified by:
-
remove
in interfaceDeque<E>
- Specified by:
-
remove
in interfaceQueue<E>
- Returns:
- the head of the queue represented by this deque
- Throws:
-
NoSuchElementException
- if this deque is empty
pop
public E pop()
Description copied from interface: Deque
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 Deque.removeFirst()
.
- Specified by:
-
pop
in interfaceDeque<E>
- Returns:
- the element at the front of this deque (which is the top of the stack represented by this deque)
- Throws:
-
NoSuchElementException
- if this deque is empty
element
public E element()
Description copied from interface: Deque
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 Deque.getFirst()
.
- Specified by:
-
element
in interfaceDeque<E>
- Specified by:
-
element
in interfaceQueue<E>
- Returns:
- the head of the queue represented by this deque
- Throws:
-
NoSuchElementException
- if this deque is empty
push
public void push(E e)
Description copied from interface: Deque
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 Deque.addFirst(E)
.
- Specified by:
-
push
in interfaceDeque<E>
- Parameters:
-
e
- the element to push - Throws:
-
NullPointerException
- if the specified element is null and this deque does not permit null elements
removeFirstOccurrence
public 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).
- Specified by:
-
removeFirstOccurrence
in interfaceDeque<E>
- Parameters:
-
o
- element to be removed from this deque, if present - Returns:
-
true
if the deque contained the specified element - Throws:
-
NullPointerException
- if the specified element is null
removeLastOccurrence
public 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).
- Specified by:
-
removeLastOccurrence
in interfaceDeque<E>
- Parameters:
-
o
- element to be removed from this deque, if present - Returns:
-
true
if the deque contained the specified element - Throws:
-
NullPointerException
- if the specified element is null
contains
public 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)
.
- Specified by:
-
contains
in interfaceCollection<E>
- Specified by:
-
contains
in interfaceDeque<E>
- Overrides:
-
contains
in classAbstractCollection<E>
- Parameters:
-
o
- element whose presence in this deque is to be tested - Returns:
-
true
if this deque contains the specified element
isEmpty
public boolean isEmpty()
Returns true
if this collection contains no elements.
- Specified by:
-
isEmpty
in interfaceCollection<E>
- Overrides:
-
isEmpty
in classAbstractCollection<E>
- Returns:
-
true
if this collection contains no elements
size
public 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.
- Specified by:
-
size
in interfaceCollection<E>
- Specified by:
-
size
in interfaceDeque<E>
- Returns:
- the number of elements in this deque
remove
public 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)
.
- Specified by:
-
remove
in interfaceCollection<E>
- Specified by:
-
remove
in interfaceDeque<E>
- Overrides:
-
remove
in classAbstractCollection<E>
- Parameters:
-
o
- element to be removed from this deque, if present - Returns:
-
true
if the deque contained the specified element - Throws:
-
NullPointerException
- if the specified element is null
addAll
public 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
.
- Specified by:
-
addAll
in interfaceCollection<E>
- Specified by:
-
addAll
in interfaceDeque<E>
- Overrides:
-
addAll
in classAbstractCollection<E>
- Parameters:
-
c
- the elements to be inserted into this deque - Returns:
-
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 - See Also:
AbstractCollection.add(Object)
clear
public void clear()
Removes all of the elements from this deque.
- Specified by:
-
clear
in interfaceCollection<E>
- Overrides:
-
clear
in classAbstractCollection<E>
toArray
public 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.
- Specified by:
-
toArray
in interfaceCollection<E>
- Overrides:
-
toArray
in classAbstractCollection<E>
- Returns:
- an array containing all of the elements in this deque
toArray
public <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. 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()
.- Specified by:
-
toArray
in interfaceCollection<E>
- Overrides:
-
toArray
in classAbstractCollection<E>
- Type Parameters:
-
T
- the component type of the array to contain the collection - Parameters:
-
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 purpose - Returns:
- 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
iterator
public 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.
- Specified by:
-
iterator
in interfaceCollection<E>
- Specified by:
-
iterator
in interfaceDeque<E>
- Specified by:
-
iterator
in interfaceIterable<E>
- Specified by:
-
iterator
in classAbstractCollection<E>
- Returns:
- an iterator over the elements in this deque in proper sequence
descendingIterator
public 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.
- Specified by:
-
descendingIterator
in interfaceDeque<E>
- Returns:
- an iterator over the elements in this deque in reverse order
spliterator
public Spliterator<E> spliterator()
Returns a Spliterator
over the elements in this deque.
The returned spliterator is weakly consistent.
The Spliterator
reports Spliterator.CONCURRENT
, Spliterator.ORDERED
, and Spliterator.NONNULL
.
- Specified by:
-
spliterator
in interfaceCollection<E>
- Specified by:
-
spliterator
in interfaceIterable<E>
- Implementation Note:
- The
Spliterator
implementstrySplit
to permit limited parallelism. - Returns:
- a
Spliterator
over the elements in this deque - Since:
- 1.8
removeIf
public boolean removeIf(Predicate<? super E> filter)
Description copied from interface: Collection
Removes all of the elements of this collection that satisfy the given predicate. Errors or runtime exceptions thrown during iteration or by the predicate are relayed to the caller.
- Specified by:
-
removeIf
in interfaceCollection<E>
- Parameters:
-
filter
- a predicate which returnstrue
for elements to be removed - Returns:
-
true
if any elements were removed - Throws:
-
NullPointerException
- if the specified filter is null
removeAll
public boolean removeAll(Collection<?> c)
Description copied from class: AbstractCollection
Removes all of this collection's elements that are also contained in the specified collection (optional operation). After this call returns, this collection will contain no elements in common with the specified collection.
- Specified by:
-
removeAll
in interfaceCollection<E>
- Overrides:
-
removeAll
in classAbstractCollection<E>
- Parameters:
-
c
- collection containing elements to be removed from this collection - Returns:
-
true
if this collection changed as a result of the call - Throws:
-
NullPointerException
- if this collection contains one or more null elements and the specified collection does not support null elements (optional), or if the specified collection is null - See Also:
-
AbstractCollection.remove(Object)
,AbstractCollection.contains(Object)
retainAll
public boolean retainAll(Collection<?> c)
Description copied from class: AbstractCollection
Retains only the elements in this collection that are contained in the specified collection (optional operation). In other words, removes from this collection all of its elements that are not contained in the specified collection.
- Specified by:
-
retainAll
in interfaceCollection<E>
- Overrides:
-
retainAll
in classAbstractCollection<E>
- Parameters:
-
c
- collection containing elements to be retained in this collection - Returns:
-
true
if this collection changed as a result of the call - Throws:
-
NullPointerException
- if this collection contains one or more null elements and the specified collection does not permit null elements (optional), or if the specified collection is null - See Also:
-
AbstractCollection.remove(Object)
,AbstractCollection.contains(Object)
forEach
public void forEach(Consumer<? super E> action)
Description copied from interface: Iterable
Performs the given action for each element of the Iterable
until all elements have been processed or the action throws an exception. Actions are performed in the order of iteration, if that order is specified. Exceptions thrown by the action are relayed to the caller.
The behavior of this method is unspecified if the action performs side-effects that modify the underlying source of elements, unless an overriding class has specified a concurrent modification policy.
- Specified by:
-
forEach
in interfaceIterable<E>
- Parameters:
-
action
- The action to be performed for each element - Throws:
-
NullPointerException
- if the specified action is null