Summary: Ctors | Methods | Inherited Methods | [Expand All]

Added in API level 1

public class

CopyOnWriteArrayList

extends Object
implements List<E> RandomAccess Cloneable Serializable

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

Class Overview

A thread-safe random-access list.

Read operations (including get(int)) do not block and may overlap with update operations. Reads reflect the results of the most recently completed operations. Aggregate operations like addAll(int, Collection) and clear() are atomic; they never expose an intermediate state.

Iterators of this list never throw ConcurrentModificationException. When an iterator is created, it keeps a copy of the list's contents. It is always safe to iterate this list, but iterations may not reflect the latest state of the list.

Iterators returned by this list and its sub lists cannot modify the underlying list. In particular, remove(), add(E) and set(E) all throw UnsupportedOperationException.

This class offers extended API beyond the List interface. It includes additional overloads for indexed search (indexOf(E, int) and lastIndexOf(E, int)) and methods for conditional adds (addIfAbsent(E) and addAllAbsent(Collection)).

Summary

Public Constructors
	CopyOnWriteArrayList() Creates a new empty instance.
	CopyOnWriteArrayList(Collection<? extends E> collection) Creates a new instance containing the elements of `collection`.
	CopyOnWriteArrayList(E[] array) Creates a new instance containing the elements of `array`.

Public Methods
synchronized boolean	add(E e) Adds the specified object at the end of this `List`.
synchronized void	add(int index, E e) Inserts the specified object into this `List` at the specified location.
synchronized boolean	addAll(Collection<? extends E> collection) Adds the objects in the specified collection to the end of this `List`.
synchronized boolean	addAll(int index, Collection<? extends E> collection) Inserts the objects in the specified collection at the specified location in this `List`.
synchronized int	addAllAbsent(Collection<? extends E> collection) Adds the elements of `collection` that are not already present in this list.
synchronized boolean	addIfAbsent(E object) Adds `object` to the end of this list if it is not already present.
synchronized void	clear() Removes all elements from this `List`, leaving it empty.
Object	clone() Creates and returns a copy of this `Object`.
boolean	contains(Object o) Tests whether this `List` contains the specified object.
boolean	containsAll(Collection<?> collection) Tests whether this `List` contains all objects contained in the specified collection.
boolean	equals(Object other) Compares this instance with the specified object and indicates if they are equal.
E	get(int index) Returns the element at the specified location in this `List`.
int	hashCode() Returns an integer hash code for this object.
int	indexOf(Object object) Searches this `List` for the specified object and returns the index of the first occurrence.
int	indexOf(E object, int from) Searches this list for `object` and returns the index of the first occurrence that is at or after `from`.
boolean	isEmpty() Returns whether this `List` contains no elements.
Iterator<E>	iterator() Returns an `Iterator` that iterates over the elements of this list as they were at the time of this method call.
int	lastIndexOf(Object object) Searches this `List` for the specified object and returns the index of the last occurrence.
int	lastIndexOf(E object, int to) Searches this list for `object` and returns the index of the last occurrence that is before `to`.
ListIterator<E>	listIterator(int index) Returns a `ListIterator` that iterates over the elements of this list as they were at the time of this method call.
ListIterator<E>	listIterator() Equivalent to `listIterator(0)`.
synchronized E	remove(int index) Removes the object at the specified location from this `List`.
synchronized boolean	remove(Object o) Removes the first occurrence of the specified object from this `List`.
synchronized boolean	removeAll(Collection<?> collection) Removes all occurrences in this `List` of each object in the specified collection.
synchronized boolean	retainAll(Collection<?> collection) Removes all objects from this `List` that are not contained in the specified collection.
synchronized E	set(int index, E e) Replaces the element at the specified location in this `List` with the specified object.
int	size() Returns the number of elements in this `List`.
List<E>	subList(int from, int to) Returns a `List` of the specified portion of this `List` from the given start index to the end index minus one.
<T> T[]	toArray(T[] contents) Returns an array containing all elements contained in this `List`.
Object[]	toArray() Returns an array containing all elements contained in this `List`.
String	toString() Returns a string containing a concise, human-readable description of this object.

[Expand]

Inherited Methods

From class java.lang.Object

Object	clone() Creates and returns a copy of this `Object`.
boolean	equals(Object o) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of `Class` that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the `wait()` methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the `wait()` methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait() Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object.
final void	wait(long millis, int nanos) Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object or until the specified timeout expires.
final void	wait(long millis) Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object or until the specified timeout expires.

From interface java.util.List

abstract boolean	add(E object) Adds the specified object at the end of this `List`.
abstract void	add(int location, E object) Inserts the specified object into this `List` at the specified location.
abstract boolean	addAll(Collection<? extends E> collection) Adds the objects in the specified collection to the end of this `List`.
abstract boolean	addAll(int location, Collection<? extends E> collection) Inserts the objects in the specified collection at the specified location in this `List`.
abstract void	clear() Removes all elements from this `List`, leaving it empty.
abstract boolean	contains(Object object) Tests whether this `List` contains the specified object.
abstract boolean	containsAll(Collection<?> collection) Tests whether this `List` contains all objects contained in the specified collection.
abstract boolean	equals(Object object) Compares the given object with the `List`, and returns true if they represent the same object using a class specific comparison.
abstract E	get(int location) Returns the element at the specified location in this `List`.
abstract int	hashCode() Returns the hash code for this `List`.
abstract int	indexOf(Object object) Searches this `List` for the specified object and returns the index of the first occurrence.
abstract boolean	isEmpty() Returns whether this `List` contains no elements.
abstract Iterator<E>	iterator() Returns an iterator on the elements of this `List`.
abstract int	lastIndexOf(Object object) Searches this `List` for the specified object and returns the index of the last occurrence.
abstract ListIterator<E>	listIterator(int location) Returns a list iterator on the elements of this `List`.
abstract ListIterator<E>	listIterator() Returns a `List` iterator on the elements of this `List`.
abstract E	remove(int location) Removes the object at the specified location from this `List`.
abstract boolean	remove(Object object) Removes the first occurrence of the specified object from this `List`.
abstract boolean	removeAll(Collection<?> collection) Removes all occurrences in this `List` of each object in the specified collection.
abstract boolean	retainAll(Collection<?> collection) Removes all objects from this `List` that are not contained in the specified collection.
abstract E	set(int location, E object) Replaces the element at the specified location in this `List` with the specified object.
abstract int	size() Returns the number of elements in this `List`.
abstract List<E>	subList(int start, int end) Returns a `List` of the specified portion of this `List` from the given start index to the end index minus one.
abstract <T> T[]	toArray(T[] array) Returns an array containing all elements contained in this `List`.
abstract Object[]	toArray() Returns an array containing all elements contained in this `List`.

From interface java.util.Collection

abstract boolean	add(E object) Attempts to add `object` to the contents of this `Collection` (optional).
abstract boolean	addAll(Collection<? extends E> collection) Attempts to add all of the objects contained in `Collection` to the contents of this `Collection` (optional).
abstract void	clear() Removes all elements from this `Collection`, leaving it empty (optional).
abstract boolean	contains(Object object) Tests whether this `Collection` contains the specified object.
abstract boolean	containsAll(Collection<?> collection) Tests whether this `Collection` contains all objects contained in the specified `Collection`.
abstract boolean	equals(Object object) Compares the argument to the receiver, and returns true if they represent the same object using a class specific comparison.
abstract int	hashCode() Returns an integer hash code for the receiver.
abstract boolean	isEmpty() Returns if this `Collection` contains no elements.
abstract Iterator<E>	iterator() Returns an instance of `Iterator` that may be used to access the objects contained by this `Collection`.
abstract boolean	remove(Object object) Removes one instance of the specified object from this `Collection` if one is contained (optional).
abstract boolean	removeAll(Collection<?> collection) Removes all occurrences in this `Collection` of each object in the specified `Collection` (optional).
abstract boolean	retainAll(Collection<?> collection) Removes all objects from this `Collection` that are not also found in the `Collection` passed (optional).
abstract int	size() Returns a count of how many objects this `Collection` contains.
abstract <T> T[]	toArray(T[] array) Returns an array containing all elements contained in this `Collection`.
abstract Object[]	toArray() Returns a new array containing all elements contained in this `Collection`.

From interface java.lang.Iterable

Public Constructors

public CopyOnWriteArrayList ()

Added in API level 1

Creates a new empty instance.

public CopyOnWriteArrayList (Collection<? extends E> collection)

Added in API level 1

Creates a new instance containing the elements of collection.

public CopyOnWriteArrayList (E[] array)

Added in API level 1

Creates a new instance containing the elements of array.

Public Methods

public synchronized boolean add (E e)

Added in API level 1

Adds the specified object at the end of this List.

Parameters

e	the object to add.

Returns

always true.

public synchronized void add (int index, E e)

Added in API level 1

Inserts the specified object into this List at the specified location. The object is inserted before the current element at the specified location. If the location is equal to the size of this List, the object is added at the end. If the location is smaller than the size of this List, then all elements beyond the specified location are moved by one position towards the end of the List.

Parameters

index	the index at which to insert.
e	the object to add.

public synchronized boolean addAll (Collection<? extends E> collection)

Added in API level 1

Adds the objects in the specified collection to the end of this List. The objects are added in the order in which they are returned from the collection's iterator.

Parameters

collection	the collection of objects.

Returns

true if this List is modified, false otherwise (i.e. if the passed collection was empty).

public synchronized boolean addAll (int index, Collection<? extends E> collection)

Added in API level 1

Inserts the objects in the specified collection at the specified location in this List. The objects are added in the order they are returned from the collection's iterator.

Parameters

index	the index at which to insert.
collection	the collection of objects to be inserted.

Returns

true if this List has been modified through the insertion, false otherwise (i.e. if the passed collection was empty).

public synchronized int addAllAbsent (Collection<? extends E> collection)

Added in API level 1

Adds the elements of collection that are not already present in this list. If collection includes a repeated value, at most one occurrence of that value will be added to this list. Elements are added at the end of this list.

Callers of this method may prefer CopyOnWriteArraySet, whose API is more appropriate for set operations.

public synchronized boolean addIfAbsent (E object)

Added in API level 1

Adds object to the end of this list if it is not already present.

Callers of this method may prefer CopyOnWriteArraySet, whose API is more appropriate for set operations.

public synchronized void clear ()

Added in API level 1

Removes all elements from this List, leaving it empty.

public Object clone ()

Added in API level 1

Creates and returns a copy of this Object. The default implementation returns a so-called "shallow" copy: It creates a new instance of the same class and then copies the field values (including object references) from this instance to the new instance. A "deep" copy, in contrast, would also recursively clone nested objects. A subclass that needs to implement this kind of cloning should call super.clone() to create the new instance and then create deep copies of the nested, mutable objects.

Returns

a copy of this object.

public boolean contains (Object o)

Added in API level 1

Tests whether this List contains the specified object.

Parameters

o	the object to search for.

Returns

true if object is an element of this List, false otherwise

public boolean containsAll (Collection<?> collection)

Added in API level 1

Tests whether this List contains all objects contained in the specified collection.

Parameters

collection	the collection of objects

Returns

true if all objects in the specified collection are elements of this List, false otherwise.

public boolean equals (Object other)

Added in API level 1

Compares this instance with the specified object and indicates if they are equal. In order to be equal, o must represent the same object as this instance using a class-specific comparison. The general contract is that this comparison should be reflexive, symmetric, and transitive. Also, no object reference other than null is equal to null.

The default implementation returns true only if this == o. See Writing a correct equals method if you intend implementing your own equals method.

The general contract for the equals and hashCode() methods is that if equals returns true for any two objects, then hashCode() must return the same value for these objects. This means that subclasses of Object usually override either both methods or neither of them.

Parameters

other	the object to compare this instance with.

Returns

true if the specified object is equal to this Object; false otherwise.

public E get (int index)

Added in API level 1

Returns the element at the specified location in this List.

Parameters

index	the index of the element to return.

Returns

the element at the specified location.

public int hashCode ()

Added in API level 1

Returns an integer hash code for this object. By contract, any two objects for which equals(Object) returns true must return the same hash code value. This means that subclasses of Object usually override both methods or neither method.

Note that hash values must not change over time unless information used in equals comparisons also changes.

See Writing a correct hashCode method if you intend implementing your own hashCode method.

Returns

this object's hash code.

public int indexOf (Object object)

Added in API level 1

Searches this List for the specified object and returns the index of the first occurrence.

Parameters

object	the object to search for.

Returns

the index of the first occurrence of the object or -1 if the object was not found.

public int indexOf (E object, int from)

Added in API level 1

Searches this list for object and returns the index of the first occurrence that is at or after from.

Returns

the index or -1 if the object was not found.

public boolean isEmpty ()

Added in API level 1

Returns whether this List contains no elements.

Returns

true if this List has no elements, false otherwise.

public Iterator<E> iterator ()

Added in API level 1

Returns an Iterator that iterates over the elements of this list as they were at the time of this method call. Changes to the list made after this method call will not be reflected by the iterator, nor will they trigger a ConcurrentModificationException.

The returned iterator does not support remove().

Returns

an iterator on the elements of this List.

public int lastIndexOf (Object object)

Added in API level 1

Searches this List for the specified object and returns the index of the last occurrence.

Parameters

object	the object to search for.

Returns

the index of the last occurrence of the object, or -1 if the object was not found.

public int lastIndexOf (E object, int to)

Added in API level 1

Searches this list for object and returns the index of the last occurrence that is before to.

Returns

the index or -1 if the object was not found.

public ListIterator<E> listIterator (int index)

Added in API level 1

Returns a ListIterator that iterates over the elements of this list as they were at the time of this method call. Changes to the list made after this method call will not be reflected by the iterator, nor will they trigger a ConcurrentModificationException.

The returned iterator does not support add(E), set(E) or remove(),

Parameters

index	the index at which to start the iteration.

Returns

a list iterator on the elements of this List.

public ListIterator<E> listIterator ()

Added in API level 1

Equivalent to listIterator(0).

Returns

a List iterator on the elements of this List

public synchronized E remove (int index)

Added in API level 1

Removes the object at the specified location from this List.

Parameters

index	the index of the object to remove.

Returns

the removed object.

public synchronized boolean remove (Object o)

Added in API level 1

Removes the first occurrence of the specified object from this List.

Parameters

o	the object to remove.

Returns

true if this List was modified by this operation, false otherwise.

public synchronized boolean removeAll (Collection<?> collection)

Added in API level 1

Removes all occurrences in this List of each object in the specified collection.

Parameters

collection	the collection of objects to remove.

Returns

true if this List is modified, false otherwise.

public synchronized boolean retainAll (Collection<?> collection)

Added in API level 1

Removes all objects from this List that are not contained in the specified collection.

Parameters

collection	the collection of objects to retain.

Returns

true if this List is modified, false otherwise.

public synchronized E set (int index, E e)

Added in API level 1

Replaces the element at the specified location in this List with the specified object. This operation does not change the size of the List.

Parameters

index	the index at which to put the specified object.
e	the object to insert.

Returns

the previous element at the index.

public int size ()

Added in API level 1

Returns the number of elements in this List.

Returns

the number of elements in this List.

public List<E> subList (int from, int to)

Added in API level 1

Returns a List of the specified portion of this List from the given start index to the end index minus one. The returned List is backed by this List so changes to it are reflected by the other.

Parameters

from	the index at which to start the sublist.
to	the index one past the end of the sublist.

Returns

a list of a portion of this List.

public T[] toArray (T[] contents)

Added in API level 1

Returns an array containing all elements contained in this List. If the specified array is large enough to hold the elements, the specified array is used, otherwise an array of the same type is created. If the specified array is used and is larger than this List, the array element following the collection elements is set to null.

Parameters

contents	the array.

Returns

an array of the elements from this List.

public Object[] toArray ()

Added in API level 1

Returns an array containing all elements contained in this List.

Returns

an array of the elements from this List.

public String toString ()

Added in API level 1

Returns a string containing a concise, human-readable description of this object. Subclasses are encouraged to override this method and provide an implementation that takes into account the object's type and data. The default implementation is equivalent to the following expression:

   getClass().getName() + '@' + Integer.toHexString(hashCode())

See Writing a useful toString method if you intend implementing your own toString method.

Returns

a printable representation of this object.

Results

Interfaces

Classes

Enums

Exceptions

CopyOnWriteArrayList

Class Overview

Summary

Public Constructors

public CopyOnWriteArrayList ()

public CopyOnWriteArrayList (Collection<? extends E> collection)

public CopyOnWriteArrayList (E[] array)

Public Methods

public synchronized boolean add (E e)

Parameters

Returns

public synchronized void add (int index, E e)

Parameters

public synchronized boolean addAll (Collection<? extends E> collection)

Parameters

Returns

public synchronized boolean addAll (int index, Collection<? extends E> collection)

Parameters

Returns

public synchronized int addAllAbsent (Collection<? extends E> collection)

public synchronized boolean addIfAbsent (E object)

public synchronized void clear ()

public Object clone ()

Returns

public boolean contains (Object o)

Parameters

Returns

public boolean containsAll (Collection<?> collection)

Parameters

Returns

public boolean equals (Object other)

Parameters

Returns

public E get (int index)

Parameters

Returns

public int hashCode ()

Returns

public int indexOf (Object object)

Parameters

Returns

public int indexOf (E object, int from)

Returns

public boolean isEmpty ()

Returns

public Iterator<E> iterator ()

Returns

public int lastIndexOf (Object object)

Parameters

Returns

public int lastIndexOf (E object, int to)

Returns

public ListIterator<E> listIterator (int index)

Parameters

Returns

public ListIterator<E> listIterator ()

Returns

public synchronized E remove (int index)

Parameters

Returns

public synchronized boolean remove (Object o)

Parameters

Returns

public synchronized boolean removeAll (Collection<?> collection)

Parameters

Returns

public synchronized boolean retainAll (Collection<?> collection)

Parameters

Returns

public synchronized E set (int index, E e)

Parameters

Returns

public int size ()

Returns

public List<E> subList (int from, int to)