java.util.concurrent
Class CopyOnWriteArrayList<E>

java.lang.Object   
  java.util.concurrent.CopyOnWriteArrayList<E>

Type Parameters:

E - the type of elements held in this collection

All Implemented Interfaces:

Serializable , Cloneable , Iterable <E>, Collection <E>, List <E>, RandomAccess

public class CopyOnWriteArrayList<E>
extends Object   
implements List   <E>, RandomAccess   , Cloneable   , Serializable   

A thread-safe variant of ArrayList in which all mutative operations (add, set, and so on) are implemented by making a fresh copy of the underlying array.

This is ordinarily too costly, but may be more efficient than alternatives when traversal operations vastly outnumber mutations, and is useful when you cannot or don't want to synchronize traversals, yet need to preclude interference among concurrent threads. The "snapshot" style iterator method uses a reference to the state of the array at the point that the iterator was created. This array never changes during the lifetime of the iterator, so interference is impossible and the iterator is guaranteed not to throw ConcurrentModificationException. The iterator will not reflect additions, removals, or changes to the list since the iterator was created. Element-changing operations on iterators themselves (remove, set, and add) are not supported. These methods throw UnsupportedOperationException.

This class is a member of the Java Collections Framework.

Since:

1.5

See Also:

Serialized Form

Constructor Summary

CopyOnWriteArrayList ()
Creates an empty list.

CopyOnWriteArrayList (Collection <? extends E> c)
Creates a list containing the elements of the specified Collection, in the order they are returned by the Collection's iterator.

CopyOnWriteArrayList (E[] toCopyIn)
Create a new CopyOnWriteArrayList holding a copy of given array.

Method Summary

boolean	add (E element) Appends the specified element to the end of this list.
void	add (int index, E element) Inserts the specified element at the specified position in this list.
boolean	addAll (Collection <? extends E> c) Appends all of the elements in the specified Collection to the end of this list, in the order that they are returned by the specified Collection's Iterator.
boolean	addAll (int index, Collection <? extends E> c) Inserts all of the elements in the specified Collection into this list, starting at the specified position.
int	addAllAbsent (Collection <? extends E> c) Appends all of the elements in the specified Collection that are not already contained in this list, to the end of this list, in the order that they are returned by the specified Collection's Iterator.
boolean	addIfAbsent (E element) Append the element if not present.
void	clear () Removes all of the elements from this list.
Object	clone () Returns a shallow copy of this list.
boolean	contains (Object elem) Returns true if this list contains the specified element.
boolean	containsAll (Collection <?> c) Returns true if this Collection contains all of the elements in the specified Collection.
boolean	equals (Object o) Compares the specified Object with this List for equality.
E	get (int index) Returns the element at the specified position in this list.
int	hashCode () Returns the hash code value for this List.
int	indexOf (E elem, int index) Searches for the first occurrence of the given argument, beginning the search at index, and testing for equality using the equals method.
int	indexOf (Object elem) Searches for the first occurrence of the given argument, testing for equality using the equals method.
boolean	isEmpty () Tests if this list has no elements.
Iterator <E>	iterator () Returns an Iterator over the elements contained in this collection.
int	lastIndexOf (E elem, int index) Searches backwards for the specified object, starting from the specified index, and returns an index to it.
int	lastIndexOf (Object elem) Returns the index of the last occurrence of the specified object in this list.
ListIterator <E>	listIterator () Returns an Iterator of the elements in this List (in proper sequence).
ListIterator <E>	listIterator (int index) Returns a ListIterator of the elements in this List (in proper sequence), starting at the specified position in the List.
E	remove (int index) Removes the element at the specified position in this list.
boolean	remove (Object o) Removes a single instance of the specified element from this list, if it is present (optional operation).
boolean	removeAll (Collection <?> c) Removes from this Collection all of its elements that are contained in the specified Collection.
boolean	retainAll (Collection <?> c) Retains only the elements in this Collection that are contained in the specified Collection (optional operation).
E	set (int index, E element) Replaces the element at the specified position in this list with the specified element.
int	size () Returns the number of elements in this list.
List <E>	subList (int fromIndex, int toIndex) Returns a view of the portion of this List between fromIndex, inclusive, and toIndex, exclusive.
Object []	toArray () Returns an array containing all of the elements in this list in the correct order.
<T> T[]	toArray (T[] a) Returns an array containing all of the elements in this list in the correct order.
String	toString () Returns a string representation of this Collection, containing the String representation of each element.

Methods inherited from class java.lang.Object

finalize , getClass , notify , notifyAll , wait , wait , wait

Constructor Detail

CopyOnWriteArrayList

public CopyOnWriteArrayList()

Creates an empty list.

CopyOnWriteArrayList

public CopyOnWriteArrayList(Collection   <? extends E> c)

Creates a list containing the elements of the specified Collection, in the order they are returned by the Collection's iterator.

Parameters:

c - the collection of initially held elements

CopyOnWriteArrayList

public CopyOnWriteArrayList(E[] toCopyIn)

Create a new CopyOnWriteArrayList holding a copy of given array.

Parameters:

toCopyIn - the array (a copy of this array is used as the internal array)

Method Detail

size

public int size()

Returns the number of elements in this list.

Specified by:

size in interface Collection <E>

Specified by:

size in interface List <E>

Returns:

the number of elements in this list.

isEmpty

public boolean isEmpty()

Tests if this list has no elements.

Specified by:

isEmpty in interface Collection <E>

Specified by:

isEmpty in interface List <E>

Returns:

true if this list has no elements; false otherwise.

contains

public boolean contains(Object    elem)

Returns true if this list contains the specified element.

Specified by:

contains in interface Collection <E>

Specified by:

contains in interface List <E>

Parameters:

elem - element whose presence in this List is to be tested.

Returns:

true if the specified element is present; false otherwise.

indexOf

public int indexOf(Object    elem)

Searches for the first occurrence of the given argument, testing for equality using the equals method.

Specified by:

indexOf in interface List <E>

Parameters:

elem - an object.

Returns:

the index of the first occurrence of the argument in this list; returns -1 if the object is not found.

See Also:

Object.equals(Object)

indexOf

public int indexOf(E elem,
                   int index)

Searches for the first occurrence of the given argument, beginning the search at index, and testing for equality using the equals method.

Parameters:

elem - an object.

index - the index to start searching from.

Returns:

the index of the first occurrence of the object argument in this List at position index or later in the List; returns -1 if the object is not found.

See Also:

Object.equals(Object)

lastIndexOf

public int lastIndexOf(Object    elem)

Returns the index of the last occurrence of the specified object in this list.

Specified by:

lastIndexOf in interface List <E>

Parameters:

elem - the desired element.

Returns:

the index of the last occurrence of the specified object in this list; returns -1 if the object is not found.

lastIndexOf

public int lastIndexOf(E elem,
                       int index)

Searches backwards for the specified object, starting from the specified index, and returns an index to it.

Parameters:

elem - the desired element.

index - the index to start searching from.

Returns:

the index of the last occurrence of the specified object in this List at position less than index in the List; -1 if the object is not found.

clone

public Object    clone()

Returns a shallow copy of this list. (The elements themselves are not copied.)

Overrides:

clone in class Object

Returns:

a clone of this list.

See Also:

Cloneable

toArray

public Object   [] toArray()

Returns an array containing all of the elements in this list in the correct order.

Specified by:

toArray in interface Collection <E>

Specified by:

toArray in interface List <E>

Returns:

an array containing all of the elements in this list in the correct order.

See Also:

Arrays.asList(Object[])

toArray

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

Returns an array containing all of the elements in this list in the correct order. The runtime type of the returned array is that of the specified array. If the list 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 list.

If the list fits in the specified array with room to spare (i.e., the array has more elements than the list), 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 list only if the caller knows that the list does not contain any null elements.

Specified by:

toArray in interface Collection <E>

Specified by:

toArray in interface List <E>

Parameters:

a - the array into which the elements of the list 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 list.

Throws:

ArrayStoreException - the runtime type of a is not a supertype of the runtime type of every element in this list.

get

public E get(int index)

Returns the element at the specified position in this list.

Specified by:

get in interface List <E>

Parameters:

index - index of element to return.

Returns:

the element at the specified position in this list.

Throws:

IndexOutOfBoundsException - if index is out of range (index < 0 || index >= size()).

set

public E set(int index,
             E element)

Replaces the element at the specified position in this list with the specified element.

Specified by:

set in interface List <E>

Parameters:

index - index of element to replace.

element - element to be stored at the specified position.

Returns:

the element previously at the specified position.

Throws:

IndexOutOfBoundsException - if index out of range (index < 0 || index >= size()).

add

public boolean add(E element)

Appends the specified element to the end of this list.

Specified by:

add in interface Collection <E>

Specified by:

add in interface List <E>

Parameters:

element - element to be appended to this list.

Returns:

true (as per the general contract of Collection.add).

add

public void add(int index,
                E element)

Inserts the specified element at the specified position in this list. Shifts the element currently at that position (if any) and any subsequent elements to the right (adds one to their indices).

Specified by:

add in interface List <E>

Parameters:

index - index at which the specified element is to be inserted.

element - element to be inserted.

Throws:

IndexOutOfBoundsException - if index is out of range (index < 0 || index > size()).

remove

public E remove(int index)

Removes the element at the specified position in this list. Shifts any subsequent elements to the left (subtracts one from their indices).

Specified by:

remove in interface List <E>

Parameters:

index - the index of the element to removed.

Returns:

the element that was removed from the list.

Throws:

IndexOutOfBoundsException - if index out of range (index < 0 || index >= size()).

remove

public boolean remove(Object    o)

Removes a single instance of the specified element from this list, if it is present (optional operation). More formally, removes an element e such that (o==null ? e==null : o.equals(e)), if the list contains one or more such elements. Returns true if the list contained the specified element (or equivalently, if the list changed as a result of the call).

Specified by:

remove in interface Collection