ConcurrentLinkedDeque

java.lang.Object
- java.util.AbstractCollection<E>
- - com.mongodb.ConcurrentLinkedDeque<E>

Type Parameters:

E - the type of elements held in this collection

All Implemented Interfaces:

Deque<E>, java.io.Serializable, java.lang.Iterable<E>, java.util.Collection<E>, java.util.Queue<E>
```
class ConcurrentLinkedDeque<E>
extends java.util.AbstractCollection<E>
implements Deque<E>, java.io.Serializable
```
A concurrent linked-list implementation of a Deque (double-ended queue). Concurrent insertion, removal, and access operations execute safely across multiple threads. Iterators are weakly consistent, returning elements reflecting the state of the deque at some point at or since the creation of the iterator. They do not throw ConcurrentModificationException, and may proceed concurrently with other operations.
This class and its iterators implement all of the optional methods of the Collection and Iterator interfaces. Like most other concurrent collection implementations, this class does not permit the use of null elements. because some null arguments and return values cannot be reliably distinguished from the absence of elements. Arbitrarily, the Collection.remove(java.lang.Object) method is mapped to removeFirstOccurrence, and Collection.add(E) is mapped to addLast.
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.
This class is Serializable, but relies on default serialization mechanisms. Usually, it is a better idea for any serializable class using a ConcurrentLinkedDeque to instead serialize a snapshot of the elements obtained by method toArray.

Nested Class Summary

Nested Classes
Modifier and Type	Class and Description
`(package private) class`	`ConcurrentLinkedDeque.CLDIterator`
`(package private) static class`	`ConcurrentLinkedDeque.Node<E>` Linked Nodes.

Field Summary

Fields
Modifier and Type	Field and Description
`private ConcurrentLinkedDeque.Node<E>`	`header` List header.
`private static long`	`serialVersionUID`
`private ConcurrentLinkedDeque.Node<E>`	`trailer` List trailer.

Constructor Summary

Constructors
Constructor and Description
`ConcurrentLinkedDeque()` Constructs an empty deque.
`ConcurrentLinkedDeque(java.util.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

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`boolean`	`add(E e)` Inserts the specified element at the tail of this deque.
`boolean`	`addAll(java.util.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.
`private static void`	`checkNotNull(java.lang.Object v)` Throws NullPointerException if argument is null.
`void`	`clear()` Removes all of the elements from this deque.
`boolean`	`contains(java.lang.Object o)` Returns `true` if this deque contains at least one element `e` such that `o.equals(e)`.
`java.util.Iterator<E>`	`descendingIterator()` Not yet implemented.
`E`	`element()` Retrieves, but does not remove, the head of the queue represented by this deque.
`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 `true` if this collection contains no elements.
`java.util.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 queue.
`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`	`peek()` Retrieves, but does not remove, the head of the queue represented by this deque, returning `null` if this deque is empty.
`E`	`peekFirst()` Retrieves, but does not remove, the first element of this deque, returning `null` if this deque is empty.
`E`	`peekLast()` Retrieves, but does not remove, the last element of this deque, returning `null` if this deque is empty.
`E`	`poll()` Retrieves and removes the head of the queue represented by this deque, or `null` if this deque is empty.
`E`	`pollFirst()` Retrieves and removes the first element of this deque, or `null` if this deque is empty.
`E`	`pollLast()` Retrieves and removes the last element of this deque, or `null` if this deque is empty.
`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.
`E`	`remove()` Retrieves and removes the head of the queue represented by this deque.
`boolean`	`remove(java.lang.Object o)` Removes the first element `e` such that `o.equals(e)`, if such an element exists in this deque.
`E`	`removeFirst()` Removes and returns the first element of this deque.
`boolean`	`removeFirstOccurrence(java.lang.Object o)` Removes the first element `e` such that `o.equals(e)`, if such an element exists in this deque.
`E`	`removeLast()` Retrieves and removes the last element of this deque.
`boolean`	`removeLastOccurrence(java.lang.Object o)` Removes the last element `e` such that `o.equals(e)`, if such an element exists in this deque.
`private E`	`screenNullResult(E v)` Returns element unless it is null, in which case throws NoSuchElementException.
`int`	`size()` Returns the number of elements in this deque.
`java.lang.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.
`private java.util.ArrayList<E>`	`toArrayList()` Creates an array list and fills it with elements of this list.
`private static boolean`	`usable(ConcurrentLinkedDeque.Node<?> n)` Returns true if given reference is non-null and isn't a header, trailer, or marker.

Methods inherited from class java.util.AbstractCollection
containsAll, removeAll, retainAll, toString

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Collection
containsAll, equals, hashCode, parallelStream, removeAll, removeIf, retainAll, spliterator, stream

Methods inherited from interface java.lang.Iterable
forEach

- Field Detail
  - serialVersionUID
```
private static final long serialVersionUID
```
    See Also:
    
    Constant Field Values
  - header
```
private final ConcurrentLinkedDeque.Node<E> header
```
    List header. First usable node is at header.forward().
  - trailer
```
private final ConcurrentLinkedDeque.Node<E> trailer
```
    List trailer. Last usable node is at trailer.back().
- Constructor Detail
  - ConcurrentLinkedDeque
```
public ConcurrentLinkedDeque()
```
    Constructs an empty deque.
  - ConcurrentLinkedDeque
```
public ConcurrentLinkedDeque(java.util.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:
    
    java.lang.NullPointerException - if the specified collection or any of its elements are null
- Method Detail
  - usable
```
private static boolean usable(ConcurrentLinkedDeque.Node<?> n)
```
    Returns true if given reference is non-null and isn't a header, trailer, or marker.
    
    Parameters:
    
    n - (possibly null) node
    
    Returns:
    
    true if n exists as a user node
  - checkNotNull
```
private static void checkNotNull(java.lang.Object v)
```
    Throws NullPointerException if argument is null.
    
    Parameters:
    
    v - the element
  - screenNullResult
```
private E screenNullResult(E v)
```
    Returns element unless it is null, in which case throws NoSuchElementException.
    
    Parameters:
    
    v - the element
    
    Returns:
    
    the element
  - toArrayList
```
private java.util.ArrayList<E> toArrayList()
```
    Creates an array list and fills it with elements of this list. Used by toArray.
    
    Returns:
    
    the array list
  - addFirst
```
public void addFirst(E e)
```
    Inserts the specified element at the front of this deque.
    
    Specified by:
    
    addFirst in interface Deque<E>
    
    Parameters:
    
    e - the element to insert
    
    Throws:
    
    java.lang.NullPointerException - if e is null and this deque does not permit null elements
  - addLast
```
public void addLast(E e)
```
    Inserts the specified element at the end of this deque. This is identical in function to the add method.
    
    Specified by:
    
    addLast in interface Deque<E>
    
    Parameters:
    
    e - the element to insert
    
    Throws:
    
    java.lang.NullPointerException - if e is null and this deque does not permit null elements
  - offerFirst
```
public boolean offerFirst(E e)
```
    Inserts the specified element at the front of this deque.
    
    Specified by:
    
    offerFirst in interface Deque<E>
    
    Parameters:
    
    e - the element to insert
    
    Returns:
    
    true always
    
    Throws:
    
    java.lang.NullPointerException - if e is null and this deque does not permit null elements
  - offerLast
```
public boolean offerLast(E e)
```
    Inserts the specified element at the end of this deque.
    This method is equivalent to add(E).
    
    Specified by:
    
    offerLast in interface Deque<E>
    
    Parameters:
    
    e - the element to insert
    
    Returns:
    
    true always
    
    Throws:
    
    java.lang.NullPointerException - if e is null and this deque does not permit null elements
  - peekFirst
```
public E peekFirst()
```
    Description copied from interface: Deque
    
    Retrieves, but does not remove, the first element of this deque, returning null if this deque is empty.
    
    Specified by:
    
    peekFirst in interface Deque<E>
    
    Returns:
    
    the first element of this deque, or null if this deque is empty
  - peekLast
```
public E peekLast()
```
    Description copied from interface: Deque
    
    Retrieves, but does not remove, the last element of this deque, returning null if this deque is empty.
    
    Specified by:
    
    peekLast in interface Deque<E>
    
    Returns:
    
    the last element of this deque, or null if this deque is empty
  - getFirst
```
public E getFirst()
```
    Description copied from interface: Deque
    
    Retrieves, but does not remove, the first element of this deque. This method differs from the peek method only in that it throws an exception if this deque is empty.
    
    Specified by:
    
    getFirst in interface Deque<E>
    
    Returns:
    
    the first element of this deque
    
    Throws:
    
    java.util.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 the peek method only in that it throws an exception if this deque is empty.
    
    Specified by:
    
    getLast in interface Deque<E>
    
    Returns:
    
    the last element of this deque
    
    Throws:
    
    java.util.NoSuchElementException - if this deque is empty
  - pollFirst
```
public E pollFirst()
```
    Description copied from interface: Deque
    
    Retrieves and removes the first element of this deque, or null if this deque is empty.
    
    Specified by:
    
    pollFirst in interface Deque<E>
    
    Returns:
    
    the first element of this deque, or null if this deque is empty
  - pollLast
```
public E pollLast()
```
    Description copied from interface: Deque
    
    Retrieves and removes the last element of this deque, or null if this deque is empty.
    
    Specified by:
    
    pollLast in interface Deque<E>
    
    Returns:
    
    the last element of this deque, or null if this deque is empty
  - removeFirst
```
public E removeFirst()
```
    Description copied from interface: Deque
    
    Removes and returns the first element of this deque. This method differs from the pollFirst method only in that it throws an exception if this deque is empty.
    
    Specified by:
    
    removeFirst in interface Deque<E>
    
    Returns:
    
    the first element of this deque
    
    Throws:
    
    java.util.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 the pollLast method only in that it throws an exception if this deque is empty.
    
    Specified by:
    
    removeLast in interface Deque<E>
    
    Returns:
    
    the last element of this deque
    
    Throws:
    
    java.util.NoSuchElementException - if this deque is empty
  - offer
```
public boolean offer(E e)
```
    Inserts the specified element at the tail of this queue.
    
    Specified by:
    
    offer in interface Deque<E>
    
    Specified by:
    
    offer in interface java.util.Queue<E>
    
    Parameters:
    
    e - the element to insert
    
    Returns:
    
    true (as specified by Queue.offer)
    
    Throws:
    
    java.lang.NullPointerException - if the specified element is null
  - add
```
public boolean add(E e)
```
    Inserts the specified element at the tail of this deque.
    
    Specified by:
    
    add in interface Deque<E>
    
    Specified by:
    
    add in interface java.util.Collection<E>
    
    Specified by:
    
    add in interface java.util.Queue<E>
    
    Overrides:
    
    add in class java.util.AbstractCollection<E>
    
    Parameters:
    
    e - the element to insert
    
    Returns:
    
    true (as specified by Collection.add(E))
    
    Throws:
    
    java.lang.NullPointerException - if the specified element is null
  - poll
```
public E poll()
```
    Description copied from interface: Deque
    
    Retrieves and removes the head of the queue represented by this deque, or null if this deque is empty. In other words, retrieves and removes the first element of this deque, or null if this deque is empty.
    This method is equivalent to Deque.pollFirst().
    
    Specified by:
    
    poll in interface Deque<E>
    
    Specified by:
    
    poll in interface java.util.Queue<E>
    
    Returns:
    
    the first element of this deque, or null if this deque is empty
  - remove
```
public E remove()
```
    Description copied from interface: Deque
    
    Retrieves and removes the head of the queue represented by this deque. This method differs from the poll method only in that it throws an exception if this deque is empty.
    This method is equivalent to Deque.removeFirst().
    
    Specified by:
    
    remove in interface Deque<E>
    
    Specified by:
    
    remove in interface java.util.Queue<E>
    
    Returns:
    
    the head of the queue represented by this deque
  - peek
```
public E peek()
```
    Description copied from interface: Deque
    
    Retrieves, but does not remove, the head of the queue represented by this deque, returning null if this deque is empty.
    This method is equivalent to Deque.peekFirst().
    
    Specified by:
    
    peek in interface Deque<E>
    
    Specified by:
    
    peek in interface java.util.Queue<E>
    
    Returns:
    
    the head of the queue represented by this deque, or null 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. This method differs from the peek method only in that it throws an exception if this deque is empty.
    This method is equivalent to Deque.getFirst().
    
    Specified by:
    
    element in interface Deque<E>
    
    Specified by:
    
    element in interface java.util.Queue<E>
    
    Returns:
    
    the head of the queue represented by this deque
  - push
```
public void push(E e)
```
    Description copied from interface: Deque
    
    Pushes an element onto the stack represented by this deque. In other words, inserts the element to the front this deque unless it would violate capacity restrictions.
    This method is equivalent to Deque.addFirst(E).
    
    Specified by:
    
    push in interface Deque<E>
  - 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 interface Deque<E>
    
    Returns:
    
    the element at the front of this deque (which is the top of the stack represented by this deque)
  - removeFirstOccurrence
```
public boolean removeFirstOccurrence(java.lang.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.
    
    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:
    
    java.lang.NullPointerException - if the specified element is null
  - removeLastOccurrence
```
public boolean removeLastOccurrence(java.lang.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.
    
    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:
    
    java.lang.NullPointerException - if the specified element is null
  - contains
```
public boolean contains(java.lang.Object o)
```
    Returns true if this deque contains at least one element e such that o.equals(e).
    
    Specified by:
    
    contains in interface java.util.Collection<E>
    
    Overrides:
    
    contains in class java.util.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 java.util.Collection<E>
    
    Overrides:
    
    isEmpty in class java.util.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 java.util.Collection<E>
    
    Specified by:
    
    size in class java.util.AbstractCollection<E>
    
    Returns:
    
    the number of elements in this deque
  - remove
```
public boolean remove(java.lang.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.
    
    Specified by:
    
    remove in interface java.util.Collection<E>
    
    Overrides:
    
    remove in class java.util.AbstractCollection<E>
    
    Parameters:
    
    o - element to be removed from this deque, if present
    
    Returns:
    
    true if the deque contained the specified element
    
    Throws:
    
    java.lang.NullPointerException - if the specified element is null
  - addAll
```
public boolean addAll(java.util.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. The behavior of this operation is undefined if the specified collection is modified while the operation is in progress. (This implies that the behavior of this call is undefined if the specified Collection is this deque, and this deque is nonempty.)
    
    Specified by:
    
    addAll in interface java.util.Collection<E>
    
    Overrides:
    
    addAll in class java.util.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:
    
    java.lang.NullPointerException - if c or any element within it is null
  - clear
```
public void clear()
```
    Removes all of the elements from this deque.
    
    Specified by:
    
    clear in interface java.util.Collection<E>
    
    Overrides:
    
    clear in class java.util.AbstractCollection<E>
  - toArray
```
public java.lang.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 java.util.Collection<E>
    
    Overrides:
    
    toArray in class java.util.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 java.util.Collection<E>
    
    Overrides:
    
    toArray in class java.util.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:
    
    java.lang.ArrayStoreException - if the runtime type of the specified array is not a supertype of the runtime type of every element in this deque
    
    java.lang.NullPointerException - if the specified array is null
  - iterator
```
public java.util.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 a "weakly consistent" iterator that will never throw ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.
    
    Specified by:
    
    iterator in interface Deque<E>
    
    Specified by:
    
    iterator in interface java.lang.Iterable<E>
    
    Specified by:
    
    iterator in interface java.util.Collection<E>
    
    Specified by:
    
    iterator in class java.util.AbstractCollection<E>
    
    Returns:
    
    an iterator over the elements in this deque in proper sequence
  - descendingIterator
```
public java.util.Iterator<E> descendingIterator()
```
    Not yet implemented.

Class ConcurrentLinkedDeque<E>

Nested Class Summary

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.util.AbstractCollection

Methods inherited from class java.lang.Object

Methods inherited from interface java.util.Collection

Methods inherited from interface java.lang.Iterable

Field Detail

serialVersionUID

header

trailer

Constructor Detail

ConcurrentLinkedDeque

ConcurrentLinkedDeque

Method Detail

usable

checkNotNull

screenNullResult

toArrayList

addFirst

addLast

offerFirst

offerLast

peekFirst

peekLast

getFirst

getLast

pollFirst

pollLast

removeFirst

removeLast

offer

add

poll

remove

peek

element

push

pop

removeFirstOccurrence

removeLastOccurrence

contains

isEmpty

size

remove

addAll

clear

toArray

toArray

iterator

descendingIterator