E - the type of elements held in this collectionpublic 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. 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.
public ConcurrentLinkedDeque()
Constructs an empty deque.
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.
c - the collection of elements to initially containNullPointerException - if the specified collection or any of its elements are nullpublic 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.
addFirst in interface Deque<E>
e - the element to addNullPointerException - if the specified element is nullpublic 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).
addLast in interface Deque<E>
e - the element to addNullPointerException - if the specified element is nullpublic 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.
offerFirst in interface Deque<E>
e - the element to addtrue (as specified by Deque.offerFirst(E))NullPointerException - if the specified element is nullpublic 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).
offerLast in interface Deque<E>
e - the element to addtrue (as specified by Deque.offerLast(E))NullPointerException - if the specified element is nullpublic E peekFirst()
Description copied from interface: Deque
Retrieves, but does not remove, the first element of this deque, or returns null if this deque is empty.
peekFirst in interface Deque<E>
null if this deque is emptypublic E peekLast()
Description copied from interface: Deque
Retrieves, but does not remove, the last element of this deque, or returns null if this deque is empty.
peekLast in interface Deque<E>
null if this deque is emptypublic 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.
getFirst in interface Deque<E>
NoSuchElementException - if this deque is emptypublic 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.
getLast in interface Deque<E>
NoSuchElementException - if this deque is emptypublic E pollFirst()
Description copied from interface: Deque
Retrieves and removes the first element of this deque, or returns null if this deque is empty.
pollFirst in interface Deque<E>
null if this deque is emptypublic E pollLast()
Description copied from interface: Deque
Retrieves and removes the last element of this deque, or returns null if this deque is empty.
pollLast in interface Deque<E>
null if this deque is emptypublic 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.
removeFirst in interface Deque<E>
NoSuchElementException - if this deque is emptypublic 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.
removeLast in interface Deque<E>
NoSuchElementException - if this deque is emptypublic 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.
offer in interface Deque<E>
offer in interface Queue<E>
e - the element to addtrue (as specified by Queue.offer(E))NullPointerException - if the specified element is nullpublic 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.
add in interface Collection<E>
add in interface Deque<E>
add in interface Queue<E>
add in class AbstractCollection<E>
e - element whose presence in this collection is to be ensuredtrue (as specified by Collection.add(E))NullPointerException - if the specified element is nullpublic E poll()
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), or returns null if this deque is empty.
This method is equivalent to Deque.pollFirst().
poll in interface Deque<E>
poll in interface Queue<E>
null if this deque is emptypublic E peek()
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), or returns null if this deque is empty.
This method is equivalent to Deque.peekFirst().
peek in interface Deque<E>
peek in interface Queue<E>
null if this deque is emptypublic 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().
remove in interface Deque<E>
remove in interface Queue<E>
NoSuchElementException - if this deque is emptypublic 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().
pop in interface Deque<E>
NoSuchElementException - if this deque is emptypublic 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().
element in interface Deque<E>
element in interface Queue<E>
NoSuchElementException - if this deque is emptypublic 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).
push in interface Deque<E>
e - the element to pushNullPointerException - if the specified element is null and this deque does not permit null elementspublic boolean removeFirstOccurrence(Object o)
Removes the first element 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 Deque<E>
o - element to be removed from this deque, if presenttrue if the deque contained the specified elementNullPointerException - if the specified element is nullpublic boolean removeLastOccurrence(Object o)
Removes the last element 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 Deque<E>
o - element to be removed from this deque, if presenttrue if the deque contained the specified elementNullPointerException - if the specified element is nullpublic boolean contains(Object o)
Returns true if this deque contains at least one element e such that o.equals(e).
contains in interface Collection<E>
contains in interface Deque<E>
contains in class AbstractCollection<E>
o - element whose presence in this deque is to be testedtrue if this deque contains the specified elementpublic boolean isEmpty()
Returns true if this collection contains no elements.
isEmpty in interface Collection<E>
isEmpty in class AbstractCollection<E>
true if this collection contains no elementspublic 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.
size in interface Collection<E>
size in interface Deque<E>
size in class AbstractCollection<E>
public boolean remove(Object o)
Removes the first element 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 Collection<E>
remove in interface Deque<E>
remove in class AbstractCollection<E>
o - element to be removed from this deque, if presenttrue if the deque contained the specified elementNullPointerException - if the specified element is nullpublic 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.
addAll in interface Collection<E>
addAll in class AbstractCollection<E>
c - the elements to be inserted into this dequetrue if this deque changed as a result of the callNullPointerException - if the specified collection or any of its elements are nullIllegalArgumentException - if the collection is this dequeAbstractCollection.add(Object)public void clear()
Removes all of the elements from this deque.
clear in interface Collection<E>
clear in class AbstractCollection<E>
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.
toArray in interface Collection<E>
toArray in class AbstractCollection<E>
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().toArray in interface Collection<E>
toArray in class AbstractCollection<E>
T - the runtime type of the array to contain the collectiona - 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 purposeArrayStoreException - 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 nullpublic 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.
iterator in interface Iterable<E>
iterator in interface Collection<E>
iterator in interface Deque<E>
iterator in class AbstractCollection<E>
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.
descendingIterator in interface Deque<E>
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.
spliterator in interface Iterable<E>
spliterator in interface Collection<E>
Spliterator implements trySplit to permit limited parallelism.Spliterator over the elements in this deque
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