org.zilonis.util.concurrent
Class ConcurrentDoublyLinkedList<E>

java.lang.Object
  java.util.AbstractCollection<E>
      org.zilonis.util.concurrent.ConcurrentDoublyLinkedList<E>

Type Parameters:

E - the type of elements held in this collection

All Implemented Interfaces:

java.io.Serializable, java.lang.Iterable<E>, java.util.Collection<E>

public class ConcurrentDoublyLinkedList<E>
extends java.util.AbstractCollection<E>
implements 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.

See Also:

Serialized Form

Constructor Summary

ConcurrentDoublyLinkedList()
Constructs an empty deque.

ConcurrentDoublyLinkedList(java.util.Collection<? extends E> c)
Constructs a deque containing the elements of the specified collection, in the order they are returned by the collection's iterator.

Method Summary

boolean	add(E e)
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 o) Prepends the given element at the beginning of this deque.
void	addLast(E o) Appends the given element to the end of this deque.
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).
E	element()
E	getFirst() Returns the first element in this deque.
E	getLast() Returns the last element in this deque.
boolean	isEmpty() Returns true if this collection contains no elements.
java.util.Iterator<E>	iterator() Returns a weakly consistent iterator over the elements in this deque, in first-to-last order.
boolean	offer(E e)
boolean	offerFirst(E o) Prepends the given element at the beginning of this deque.
boolean	offerLast(E o) Appends the given element to the end of this deque.
E	peek()
E	peekFirst() Retrieves, but does not remove, the first element of this deque, or returns null if this deque is empty.
E	peekLast() Retrieves, but does not remove, the last element of this deque, or returns null if this deque is empty.
E	poll()
E	pollFirst() Retrieves and removes the first element of this deque, or returns null if this deque is empty.
E	pollLast() Retrieves and removes the last element of this deque, or returns null if this deque is empty.
E	pop()
void	push(E e)
E	remove()
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 from 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() Removes and returns the last element from 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.
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 the correct order.
<T> T[]	toArray(T[] a) Returns an array containing all of the elements in this deque in the correct order; the runtime type of the returned array is that of the specified array.

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

equals, hashCode

Constructor Detail

ConcurrentDoublyLinkedList

public ConcurrentDoublyLinkedList()

Constructs an empty deque.

ConcurrentDoublyLinkedList

public ConcurrentDoublyLinkedList(java.util.Collection<? extends E> c)

Constructs a deque containing the elements of the specified collection, in the order they are returned by the collection's iterator.

Parameters:

c - the collection whose elements are to be placed into this deque.

Throws:

java.lang.NullPointerException - if c or any element within it is null

Method Detail

addFirst

public void addFirst(E o)

Prepends the given element at the beginning of this deque.

Parameters:

o - the element to be inserted at the beginning of this deque.

Throws:

java.lang.NullPointerException - if the specified element is null

addLast

public void addLast(E o)

Appends the given element to the end of this deque. This is identical in function to the add method.

Parameters:

o - the element to be inserted at the end of this deque.

Throws:

java.lang.NullPointerException - if the specified element is null

offerFirst

public boolean offerFirst(E o)

Prepends the given element at the beginning of this deque.

Parameters:

o - the element to be inserted at the beginning of this deque.

Returns:

true always

Throws:

java.lang.NullPointerException - if the specified element is null

offerLast

public boolean offerLast(E o)

Appends the given element to the end of this deque. (Identical in function to the add method; included only for consistency.)

Parameters:

o - the element to be inserted at the end of this deque.

Returns:

true always

Throws:

java.lang.NullPointerException - if the specified element is null

peekFirst

public E peekFirst()

Retrieves, but does not remove, the first element of this deque, or returns null if this deque is empty.

Returns:

the first element of this queue, or null if empty.

peekLast

public E peekLast()

Retrieves, but does not remove, the last element of this deque, or returns null if this deque is empty.

Returns:

the last element of this deque, or null if empty.

getFirst

public E getFirst()

Returns the first element in this deque.

Returns:

the first element in this deque.

Throws:

java.util.NoSuchElementException - if this deque is empty.

getLast

public E getLast()

Returns the last element in this deque.

Returns:

the last element in this deque.

Throws:

java.util.NoSuchElementException - if this deque is empty.

pollFirst

public E pollFirst()

Retrieves and removes the first element of this deque, or returns null if this deque is empty.

Returns:

the first element of this deque, or null if empty.

pollLast

public E pollLast()

Retrieves and removes the last element of this deque, or returns null if this deque is empty.

Returns:

the last element of this deque, or null if empty.

removeFirst

public E removeFirst()

Removes and returns the first element from this deque.

Returns:

the first element from this deque.

Throws:

java.util.NoSuchElementException - if this deque is empty.

removeLast

public E removeLast()

Removes and returns the last element from this deque.

Returns:

the last element from this deque.

Throws:

java.util.NoSuchElementException - if this deque is empty.

offer

public boolean offer(E e)

add

public boolean add(E e)

Specified by:

add in interface java.util.Collection<E>

Overrides:

add in class java.util.AbstractCollection<E>

poll

public E poll()

remove

public E remove()

peek

public E peek()

element

public E element()

push

public void push(E e)

pop

public E pop()

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.

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.

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 the correct order.

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 in the correct order.

toArray

public <T> T[] toArray(T[] a)

Returns an array containing all of the elements in this deque in the correct order; 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 the deque fits in the specified array with room to spare (i.e., the array has more elements than the deque), the element in the array immediately following the end of the collection is set to null. This is useful in determining the length of the deque only if the caller knows that the deque does not contain any null elements.

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 the elements of the deque.

Throws:

java.lang.ArrayStoreException - if the runtime type of a 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 a weakly consistent iterator over the elements in this deque, in first-to-last order. The next method returns elements reflecting the state of the deque at some point at or since the creation of the iterator. The method does not throw ConcurrentModificationException, and may proceed concurrently with other operations.

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