Module java.base
Package java.util.concurrent

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
Author:
Doug Lea, Martin Buchholz
See Also:

  • Constructor Details

    • 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 Details

    • 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 interface Deque<E>
      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 interface Deque<E>
      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 interface Deque<E>
      Returns:
      true (as specified by Deque.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 interface Deque<E>
      Returns:
      true (as specified by Deque.offerLast(E))
      Throws:
      NullPointerException - if the specified element is null

    • peekFirst

      public E peekFirst()
      Specified by:
      peekFirst in interface Deque<E>

    • peekLast

      public E peekLast()
      Specified by:
      peekLast in interface Deque<E>

    • getFirst

      public E getFirst()
      Specified by:
      getFirst in interface Deque<E>
      Throws:
      NoSuchElementException

    • getLast

      public E getLast()
      Specified by:
      getLast in interface Deque<E>
      Throws:
      NoSuchElementException

    • pollFirst

      public E pollFirst()
      Specified by:
      pollFirst in interface Deque<E>

    • pollLast

      public E pollLast()
      Specified by:
      pollLast in interface Deque<E>

    • removeFirst

      public E removeFirst()
      Specified by:
      removeFirst in interface Deque<E>
      Throws:
      NoSuchElementException

    • removeLast

      public E removeLast()
      Specified by:
      removeLast in interface Deque<E>
      Throws:
      NoSuchElementException

    • 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 interface Deque<E>
      Specified by:
      offer in interface Queue<E>
      Returns:
      true (as specified by Queue.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 interface Collection<E>
      Specified by:
      add in interface Deque<E>
      Specified by:
      add in interface Queue<E>
      Overrides:
      add in class AbstractCollection<E>
      Returns:
      true (as specified by Collection.add(E))
      Throws:
      NullPointerException - if the specified element is null

    • poll

      public E poll()
      Specified by:
      poll in interface Deque<E>
      Specified by:
      poll in interface Queue<E>

    • peek

      public E peek()
      Specified by:
      peek in interface Deque<E>
      Specified by:
      peek in interface Queue<E>

    • remove

      public E remove()
      Specified by:
      remove in interface Deque<E>
      Specified by:
      remove in interface Queue<E>
      Throws:
      NoSuchElementException

    • pop

      public E pop()
      Specified by:
      pop in interface Deque<E>
      Throws:
      NoSuchElementException

    • element

      public E element()
      Specified by:
      element in interface Deque<E>
      Specified by:
      element in interface Queue<E>
      Throws:
      NoSuchElementException

    • push

      public void push(E e)
      Specified by:
      push in interface Deque<E>
      Throws:
      NullPointerException

    • 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 interface Deque<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 interface Deque<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 interface Collection<E>
      Specified by:
      contains in interface Deque<E>
      Overrides:
      contains in class AbstractCollection<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 interface Collection<E>
      Overrides:
      isEmpty in class AbstractCollection<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 interface Collection<E>
      Specified by:
      size in interface Deque<E>
      Specified by:
      size in class AbstractCollection<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 interface Collection<E>
      Specified by:
      remove in interface Deque<E>
      Overrides:
      remove in class AbstractCollection<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 interface Collection<E>
      Specified by:
      addAll in interface Deque<E>
      Overrides:
      addAll in class AbstractCollection<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

    • clear

      public void clear()
      Removes all of the elements from this deque.
      Specified by:
      clear in interface Collection<E>
      Overrides:
      clear in class AbstractCollection<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 interface Collection<E>
      Overrides:
      toArray in class AbstractCollection<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 interface Collection<E>
      Overrides:
      toArray in class AbstractCollection<E>
      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 interface Collection<E>
      Specified by:
      iterator in interface Deque<E>
      Specified by:
      iterator in interface Iterable<E>
      Specified by:
      iterator in class AbstractCollection<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 interface Deque<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 interface Collection<E>
      Specified by:
      spliterator in interface Iterable<E>
      Returns:
      a Spliterator over the elements in this deque
      Since:
      1.8
      Implementation Note:
      The Spliterator implements trySplit to permit limited parallelism.

    • removeIf

      public boolean removeIf(Predicate<? super E> filter)
      Specified by:
      removeIf in interface Collection<E>
      Throws:
      NullPointerException

    • removeAll

      public boolean removeAll(Collection<?> c)
      Specified by:
      removeAll in interface Collection<E>
      Overrides:
      removeAll in class AbstractCollection<E>
      Throws:
      NullPointerException

    • retainAll

      public boolean retainAll(Collection<?> c)
      Specified by:
      retainAll in interface Collection<E>
      Overrides:
      retainAll in class AbstractCollection<E>
      Throws:
      NullPointerException

    • forEach

      public void forEach(Consumer<? super E> action)
      Specified by:
      forEach in interface Iterable<E>
      Throws:
      NullPointerException