- java.lang.Object
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- java.util.AbstractCollection<E>
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- java.util.concurrent.ConcurrentLinkedDeque<E>
 
 
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- 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. AConcurrentLinkedDequeis 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 ofnullelements.Iterators and spliterators are weakly consistent. Beware that, unlike in most collections, the sizemethod 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>)orforEach(java.util.function.Consumer<? super E>), are not guaranteed to be performed atomically. For example, aforEachtraversal concurrent with anaddAlloperation might observe only some of the added elements.This class and its iterator implement all of the optional methods of the DequeandIteratorinterfaces.Memory consistency effects: As with other concurrent collections, actions in a thread prior to placing an object into a ConcurrentLinkedDequehappen-before actions subsequent to the access or removal of that element from theConcurrentLinkedDequein another thread.This class is a member of the Java Collections Framework. - Since:
- 1.7
- See Also:
- Serialized Form
 
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Constructor SummaryConstructors 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.
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Method SummaryAll Methods Instance Methods Concrete Methods Modifier and Type Method Description booleanadd(E e)Inserts 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.voidaddFirst(E e)Inserts the specified element at the front of this deque.voidaddLast(E e)Inserts the specified element at the end of this deque.voidclear()Removes all of the elements from this deque.booleancontains(Object o)Returnstrueif this deque contains the specified element.Iterator<E>descendingIterator()Returns an iterator over the elements in this deque in reverse sequential order.Eelement()Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque).voidforEach(Consumer<? super E> action)Performs the given action for each element of theIterableuntil all elements have been processed or the action throws an exception.EgetFirst()Retrieves, but does not remove, the first element of this deque.EgetLast()Retrieves, but does not remove, the last element of this deque.booleanisEmpty()Returnstrueif this collection contains no elements.Iterator<E>iterator()Returns an iterator over the elements in this deque in proper sequence.booleanoffer(E e)Inserts the specified element at the tail of this deque.booleanofferFirst(E e)Inserts the specified element at the front of this deque.booleanofferLast(E e)Inserts the specified element at the end of this deque.Epop()Pops an element from the stack represented by this deque.voidpush(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 anIllegalStateExceptionif no space is currently available.Eremove()Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque).booleanremove(Object o)Removes 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).EremoveFirst()Retrieves and removes the first element of this deque.booleanremoveFirstOccurrence(Object o)Removes the first occurrence of the specified element from this deque.booleanremoveIf(Predicate<? super E> filter)Removes all of the elements of this collection that satisfy the given predicate.EremoveLast()Retrieves and removes the last element of this deque.booleanremoveLastOccurrence(Object o)Removes 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.Spliterator<E>spliterator()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.AbstractCollectioncontainsAll, toString
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Methods declared in class java.lang.Objectclone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
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Methods declared in interface java.util.CollectioncontainsAll, equals, hashCode, parallelStream, stream, toArray
 
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Constructor Detail- 
ConcurrentLinkedDequepublic ConcurrentLinkedDeque() Constructs an empty deque.
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ConcurrentLinkedDequepublic 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
 
 
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Method Detail- 
addFirstpublic void addFirst(E e) Inserts the specified element at the front of this deque. As the deque is unbounded, this method will never throwIllegalStateException.- Specified by:
- addFirstin interface- Deque<E>
- Parameters:
- e- the element to add
- Throws:
- NullPointerException- if the specified element is null
 
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addLastpublic void addLast(E e) 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 interface- Deque<E>
- Parameters:
- e- the element to add
- Throws:
- NullPointerException- if the specified element is null
 
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offerFirstpublic boolean offerFirst(E e) Inserts the specified element at the front of this deque. As the deque is unbounded, this method will never returnfalse.- Specified by:
- offerFirstin interface- Deque<E>
- Parameters:
- e- the element to add
- Returns:
- true(as specified by- Deque.offerFirst(E))
- Throws:
- NullPointerException- if the specified element is null
 
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offerLastpublic boolean offerLast(E e) 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 interface- Deque<E>
- Parameters:
- e- the element to add
- Returns:
- true(as specified by- Deque.offerLast(E))
- Throws:
- NullPointerException- if the specified element is null
 
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getFirstpublic E 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 interface- Deque<E>
- Returns:
- the head of this deque
- Throws:
- NoSuchElementException- if this deque is empty
 
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getLastpublic E 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 interface- Deque<E>
- Returns:
- the tail of this deque
- Throws:
- NoSuchElementException- if this deque is empty
 
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removeFirstpublic E 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 interface- Deque<E>
- Returns:
- the head of this deque
- Throws:
- NoSuchElementException- if this deque is empty
 
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removeLastpublic E 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 interface- Deque<E>
- Returns:
- the tail of this deque
- Throws:
- NoSuchElementException- if this deque is empty
 
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offerpublic boolean offer(E e) Inserts the specified element at the tail of this deque. As the deque is unbounded, this method will never returnfalse.- Specified by:
- offerin interface- Deque<E>
- Specified by:
- offerin interface- Queue<E>
- Parameters:
- e- the element to add
- Returns:
- true(as specified by- Queue.offer(E))
- Throws:
- NullPointerException- if the specified element is null
 
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addpublic boolean add(E e) Inserts the specified element at the tail of this deque. As the deque is unbounded, this method will never throwIllegalStateExceptionor returnfalse.- Specified by:
- addin interface- Collection<E>
- Specified by:
- addin interface- Deque<E>
- Specified by:
- addin interface- Queue<E>
- Overrides:
- addin class- AbstractCollection<E>
- Parameters:
- e- element whose presence in this collection is to be ensured
- Returns:
- true(as specified by- Collection.add(E))
- Throws:
- NullPointerException- if the specified element is null
 
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removepublic E 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().
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poppublic E 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 interface- Deque<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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elementpublic E 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().
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pushpublic void push(E e) 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 interface- Deque<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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removeFirstOccurrencepublic 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 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 interface- Deque<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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removeLastOccurrencepublic 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 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 interface- Deque<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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containspublic boolean contains(Object o) 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 interface- Collection<E>
- Specified by:
- containsin interface- Deque<E>
- Overrides:
- containsin class- AbstractCollection<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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isEmptypublic boolean isEmpty() Returnstrueif this collection contains no elements.- Specified by:
- isEmptyin interface- Collection<E>
- Overrides:
- isEmptyin class- AbstractCollection<E>
- Returns:
- trueif this collection contains no elements
 
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sizepublic 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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removepublic 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 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 interface- Collection<E>
- Specified by:
- removein interface- Deque<E>
- Overrides:
- removein class- AbstractCollection<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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addAllpublic 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 toaddAllof a deque to itself result inIllegalArgumentException.- Specified by:
- addAllin interface- Collection<E>
- Specified by:
- addAllin interface- Deque<E>
- Overrides:
- addAllin class- AbstractCollection<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 null
- IllegalArgumentException- if the collection is this deque
- See Also:
- AbstractCollection.add(Object)
 
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clearpublic void clear() Removes all of the elements from this deque.- Specified by:
- clearin interface- Collection<E>
- Overrides:
- clearin class- AbstractCollection<E>
 
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toArraypublic 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:
- toArrayin interface- Collection<E>
- Overrides:
- toArrayin class- AbstractCollection<E>
- Returns:
- an array containing all of the elements in this deque
 
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toArraypublic <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 interface- Collection<E>
- Overrides:
- toArrayin class- AbstractCollection<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
 
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iteratorpublic 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. 
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descendingIteratorpublic 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:
- descendingIteratorin interface- Deque<E>
- Returns:
- an iterator over the elements in this deque in reverse order
 
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spliteratorpublic Spliterator<E> spliterator() Returns aSpliteratorover the elements in this deque.The returned spliterator is weakly consistent. The SpliteratorreportsSpliterator.CONCURRENT,Spliterator.ORDERED, andSpliterator.NONNULL.- Specified by:
- spliteratorin interface- Collection<E>
- Specified by:
- spliteratorin interface- Iterable<E>
- Implementation Note:
- The SpliteratorimplementstrySplitto permit limited parallelism.
- Returns:
- a Spliteratorover the elements in this deque
- Since:
- 1.8
 
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removeIfpublic boolean removeIf(Predicate<? super E> filter) 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 interface- Collection<E>
- Parameters:
- filter- a predicate which returns- truefor elements to be removed
- Returns:
- trueif any elements were removed
- Throws:
- NullPointerException- if the specified filter is null
 
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removeAllpublic boolean removeAll(Collection<?> c) 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 interface- Collection<E>
- Overrides:
- removeAllin class- AbstractCollection<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:
- AbstractCollection.remove(Object),- AbstractCollection.contains(Object)
 
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retainAllpublic boolean retainAll(Collection<?> c) 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 interface- Collection<E>
- Overrides:
- retainAllin class- AbstractCollection<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:
- AbstractCollection.remove(Object),- AbstractCollection.contains(Object)
 
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forEachpublic void forEach(Consumer<? super E> action) 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 interface- Iterable<E>
- Parameters:
- action- The action to be performed for each element
- Throws:
- NullPointerException- if the specified action is null
 
 
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