- Type Parameters:
E- the type of elements held in this deque
- All Implemented Interfaces:
Serializable,Iterable<E>,Collection<E>,Deque<E>,Queue<E>
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:
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Constructor Summary
ConstructorsConstructorDescriptionConstructs 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 TypeMethodDescriptionbooleanInserts the specified element at the tail of this deque.booleanaddAll(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.voidInserts the specified element at the front of this deque.voidInserts the specified element at the end of this deque.voidclear()Removes all of the elements from this deque.booleanReturnstrueif this deque contains the specified element.Returns an iterator over the elements in this deque in reverse sequential order.element()Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque).voidPerforms the given action for each element of theIterableuntil all elements have been processed or the action throws an exception.getFirst()Retrieves, but does not remove, the first element of this deque.getLast()Retrieves, but does not remove, the last element of this deque.booleanisEmpty()Returnstrueif this collection contains no elements.iterator()Returns an iterator over the elements in this deque in proper sequence.booleanInserts the specified element at the tail of this deque.booleanofferFirst(E e) Inserts the specified element at the front of this deque.booleanInserts the specified element at the end of this deque.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 returnsnullif this deque is empty.Retrieves, but does not remove, the first element of this deque, or returnsnullif this deque is empty.peekLast()Retrieves, but does not remove, the last element of this deque, or returnsnullif this deque is empty.poll()Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), or returnsnullif this deque is empty.Retrieves and removes the first element of this deque, or returnsnullif this deque is empty.pollLast()Retrieves and removes the last element of this deque, or returnsnullif this deque is empty.pop()Pops an element from the stack represented by this deque.voidPushes 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 anIllegalStateExceptionif no space is currently available.remove()Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque).booleanRemoves the first occurrence of the specified element from this deque.booleanremoveAll(Collection<?> c) Removes all of this collection's elements that are also contained in the specified collection (optional operation).Retrieves and removes the first element of this deque.booleanRemoves the first occurrence of the specified element from this deque.booleanRemoves all of the elements of this collection that satisfy the given predicate.Retrieves and removes the last element of this deque.booleanRemoves the last occurrence of the specified element from this deque.booleanretainAll(Collection<?> c) Retains only the elements in this collection that are contained in the specified collection (optional operation).intsize()Returns the number of elements in this deque.Returns aSpliteratorover 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).<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, toStringMethods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, waitMethods declared in interface java.util.Collection
containsAll, equals, hashCode, parallelStream, stream, toArray
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Constructor Details
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ConcurrentLinkedDeque
public ConcurrentLinkedDeque()Constructs an empty deque. -
ConcurrentLinkedDeque
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
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Method Details
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addFirst
Inserts the specified element at the front of this deque. As the deque is unbounded, this method will never throwIllegalStateException.- Specified by:
addFirstin interfaceDeque<E>- Parameters:
e- the element to add- Throws:
NullPointerException- if the specified element is null
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addLast
Inserts the specified element at the end of this deque. As the deque is unbounded, this method will never throwIllegalStateException.This method is equivalent to
add(E).- Specified by:
addLastin interfaceDeque<E>- Parameters:
e- the element to add- Throws:
NullPointerException- if the specified element is null
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offerFirst
Inserts the specified element at the front of this deque. As the deque is unbounded, this method will never returnfalse.- Specified by:
offerFirstin interfaceDeque<E>- Parameters:
e- the element to add- Returns:
true(as specified byDeque.offerFirst(E))- Throws:
NullPointerException- if the specified element is null
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offerLast
Inserts the specified element at the end of this deque. As the deque is unbounded, this method will never returnfalse.This method is equivalent to
add(E).- Specified by:
offerLastin interfaceDeque<E>- Parameters:
e- the element to add- Returns:
true(as specified byDeque.offerLast(E))- Throws:
NullPointerException- if the specified element is null
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peekFirst
Description copied from interface:DequeRetrieves, but does not remove, the first element of this deque, or returnsnullif this deque is empty. -
peekLast
Description copied from interface:DequeRetrieves, but does not remove, the last element of this deque, or returnsnullif this deque is empty. -
getFirst
Description copied from interface:DequeRetrieves, but does not remove, the first element of this deque. This method differs frompeekFirstonly in that it throws an exception if this deque is empty.- Specified by:
getFirstin interfaceDeque<E>- Returns:
- the head of this deque
- Throws:
NoSuchElementException- if this deque is empty
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getLast
Description copied from interface:DequeRetrieves, but does not remove, the last element of this deque. This method differs frompeekLastonly in that it throws an exception if this deque is empty.- Specified by:
getLastin interfaceDeque<E>- Returns:
- the tail of this deque
- Throws:
NoSuchElementException- if this deque is empty
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pollFirst
Description copied from interface:DequeRetrieves and removes the first element of this deque, or returnsnullif this deque is empty. -
pollLast
Description copied from interface:DequeRetrieves and removes the last element of this deque, or returnsnullif this deque is empty. -
removeFirst
Description copied from interface:DequeRetrieves and removes the first element of this deque. This method differs frompollFirstonly in that it throws an exception if this deque is empty.- Specified by:
removeFirstin interfaceDeque<E>- Returns:
- the head of this deque
- Throws:
NoSuchElementException- if this deque is empty
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removeLast
Description copied from interface:DequeRetrieves and removes the last element of this deque. This method differs frompollLastonly in that it throws an exception if this deque is empty.- Specified by:
removeLastin interfaceDeque<E>- Returns:
- the tail of this deque
- Throws:
NoSuchElementException- if this deque is empty
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offer
Inserts the specified element at the tail of this deque. As the deque is unbounded, this method will never returnfalse.- Specified by:
offerin interfaceDeque<E>- Specified by:
offerin interfaceQueue<E>- Parameters:
e- the element to add- Returns:
true(as specified byQueue.offer(E))- Throws:
NullPointerException- if the specified element is null
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add
Inserts the specified element at the tail of this deque. As the deque is unbounded, this method will never throwIllegalStateExceptionor returnfalse.- Specified by:
addin interfaceCollection<E>- Specified by:
addin interfaceDeque<E>- Specified by:
addin interfaceQueue<E>- Overrides:
addin 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
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poll
Description copied from interface:DequeRetrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), or returnsnullif this deque is empty.This method is equivalent to
Deque.pollFirst(). -
peek
Description copied from interface:DequeRetrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque), or returnsnullif this deque is empty.This method is equivalent to
Deque.peekFirst(). -
remove
Description copied from interface:DequeRetrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque). This method differs frompoll()only in that it throws an exception if this deque is empty.This method is equivalent to
Deque.removeFirst(). -
pop
Description copied from interface:DequePops 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:
popin 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
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element
Description copied from interface:DequeRetrieves, 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 frompeekonly in that it throws an exception if this deque is empty.This method is equivalent to
Deque.getFirst(). -
push
Description copied from interface:DequePushes 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 anIllegalStateExceptionif no space is currently available.This method is equivalent to
Deque.addFirst(E).- Specified by:
pushin interfaceDeque<E>- Parameters:
e- the element to push- Throws:
NullPointerException- if the specified element is null and this deque does not permit null elements
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removeFirstOccurrence
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 elementesuch thato.equals(e)(if such an element exists). Returnstrueif this deque contained the specified element (or equivalently, if this deque changed as a result of the call).- Specified by:
removeFirstOccurrencein interfaceDeque<E>- Parameters:
o- element to be removed from this deque, if present- Returns:
trueif the deque contained the specified element- Throws:
NullPointerException- if the specified element is null
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removeLastOccurrence
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 elementesuch thato.equals(e)(if such an element exists). Returnstrueif this deque contained the specified element (or equivalently, if this deque changed as a result of the call).- Specified by:
removeLastOccurrencein interfaceDeque<E>- Parameters:
o- element to be removed from this deque, if present- Returns:
trueif the deque contained the specified element- Throws:
NullPointerException- if the specified element is null
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contains
Returnstrueif this deque contains the specified element. More formally, returnstrueif and only if this deque contains at least one elementesuch thato.equals(e).- Specified by:
containsin interfaceCollection<E>- Specified by:
containsin interfaceDeque<E>- Overrides:
containsin classAbstractCollection<E>- Parameters:
o- element whose presence in this deque is to be tested- Returns:
trueif this deque contains the specified element
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isEmpty
public boolean isEmpty()Returnstrueif this collection contains no elements.- Specified by:
isEmptyin interfaceCollection<E>- Overrides:
isEmptyin classAbstractCollection<E>- Returns:
trueif this collection contains no elements
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size
public int size()Returns the number of elements in this deque. If this deque contains more thanInteger.MAX_VALUEelements, it returnsInteger.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.
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remove
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 elementesuch thato.equals(e)(if such an element exists). Returnstrueif 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:
removein interfaceCollection<E>- Specified by:
removein interfaceDeque<E>- Overrides:
removein classAbstractCollection<E>- Parameters:
o- element to be removed from this deque, if present- Returns:
trueif the deque contained the specified element- Throws:
NullPointerException- if the specified element is null
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addAll
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 toaddAllof a deque to itself result inIllegalArgumentException.- Specified by:
addAllin interfaceCollection<E>- Specified by:
addAllin interfaceDeque<E>- Overrides:
addAllin classAbstractCollection<E>- Parameters:
c- the elements to be inserted into this deque- Returns:
trueif this deque changed as a result of the call- Throws:
NullPointerException- if the specified collection or any of its elements are nullIllegalArgumentException- if the collection is this deque- See Also:
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clear
public void clear()Removes all of the elements from this deque.- Specified by:
clearin interfaceCollection<E>- Overrides:
clearin classAbstractCollection<E>
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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:
toArrayin interfaceCollection<E>- Overrides:
toArrayin classAbstractCollection<E>- Returns:
- an array containing all of the elements in this deque
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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
xis a deque known to contain only strings. The following code can be used to dump the deque into a newly allocated array ofString:
Note thatString[] y = x.toArray(new String[0]);toArray(new Object[0])is identical in function totoArray().- Specified by:
toArrayin interfaceCollection<E>- Overrides:
toArrayin 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 dequeNullPointerException- if the specified array is null
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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.
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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:
descendingIteratorin interfaceDeque<E>- Returns:
- an iterator over the elements in this deque in reverse order
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spliterator
Returns aSpliteratorover the elements in this deque.The returned spliterator is weakly consistent.
The
SpliteratorreportsSpliterator.CONCURRENT,Spliterator.ORDERED, andSpliterator.NONNULL.- Specified by:
spliteratorin interfaceCollection<E>- Specified by:
spliteratorin interfaceIterable<E>- Implementation Note:
- The
SpliteratorimplementstrySplitto permit limited parallelism. - Returns:
- a
Spliteratorover the elements in this deque - Since:
- 1.8
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removeIf
Description copied from interface:CollectionRemoves 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:
removeIfin interfaceCollection<E>- Parameters:
filter- a predicate which returnstruefor elements to be removed- Returns:
trueif any elements were removed- Throws:
NullPointerException- if the specified filter is null
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removeAll
Description copied from class:AbstractCollectionRemoves 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:
removeAllin interfaceCollection<E>- Overrides:
removeAllin classAbstractCollection<E>- Parameters:
c- collection containing elements to be removed from this collection- Returns:
trueif 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:
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retainAll
Description copied from class:AbstractCollectionRetains 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:
retainAllin interfaceCollection<E>- Overrides:
retainAllin classAbstractCollection<E>- Parameters:
c- collection containing elements to be retained in this collection- Returns:
trueif 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:
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forEach
Description copied from interface:IterablePerforms the given action for each element of theIterableuntil 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:
forEachin interfaceIterable<E>- Parameters:
action- The action to be performed for each element- Throws:
NullPointerException- if the specified action is null
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