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

public class

CopyOnWriteArraySet

extends AbstractSet<E>
implements Serializable

java.lang.Object
↳	java.util.AbstractCollection<E>
	↳	java.util.AbstractSet<E>
		↳	java.util.concurrent.CopyOnWriteArraySet<E>

Class Overview

A Set that uses CopyOnWriteArrayList for all of its operations. Thus, it shares the same basic properties:

It is best suited for applications in which set sizes generally stay small, read-only operations vastly outnumber mutative operations, and you need to prevent interference among threads during traversal.
Mutative operations(add, set, remove, etc) are expensive since they usually entail copying the entire underlying array.
Iterators do not support the mutative remove operation
Traversal via iterators is very fast and cannot ever encounter interference from other threads. Iterators rely on unchanging snapshots of the array at the time the iterators were constructed.

Sample Usage. Probably the main application of copy-on-write sets are classes that maintain sets of Handler objects that must be multicasted to upon an update command. This is a classic case where you do not want to be holding a lock while sending a message, and where traversals normally vastly overwhelm additions.

 class Handler { void handle(); ... }

 class X {
    private final CopyOnWriteArraySet<Handler> handlers = new CopyOnWriteArraySet<Handler>();
    public void addHandler(Handler h) { handlers.add(h); }

    private long internalState;
    private synchronized void changeState() { internalState = ...; }

    public void update() {
       changeState();
       Iterator it = handlers.iterator();
       while (it.hasNext())
          it.next().handle();
    }
 }

Summary

Public Constructors
	CopyOnWriteArraySet() Creates an empty set.
	CopyOnWriteArraySet(Collection<? extends E> c) Creates a set containing all of the elements of the specified Collection.

Public Methods
boolean	add(E o) If the specified element is not contained within this collection, and addition of this element succeeds, then true will be returned.
boolean	addAll(Collection<? extends E> c) Adds the objects in the specified Collection to this Collection.
void	clear() Removes all the elements in this collection.
boolean	contains(Object o) Searches this Collection for the specified object.
boolean	containsAll(Collection<?> c) Searches this Collection for all objects in the specified Collection.
boolean	isEmpty() Returns true if the collection has no element, otherwise false.
Iterator<E>	iterator() Returns an Iterator on the elements of this Collection.
boolean	remove(Object o) Removes the first occurrence of the specified object from this Collection.
boolean	removeAll(Collection<?> c) Removes all occurrences in this Collection of each object in the specified Collection.
boolean	retainAll(Collection<?> c) Removes all objects from this Collection that are not contained in the specified Collection.
int	size() Returns the number of elements in this Collection.
<T> T[]	toArray(T[] a) Returns an array containing all elements contained in this Collection.
Object[]	toArray() Returns a new array containing all elements contained in this Collection.

[Expand]

Inherited Methods

From class java.util.AbstractSet

From class java.util.AbstractCollection

boolean	add(E object) If the specified element is not contained within this collection, and addition of this element succeeds, then true will be returned.
boolean	addAll(Collection<? extends E> collection) Adds the objects in the specified Collection to this Collection.
void	clear() Removes all the elements in this collection.
boolean	contains(Object object) Searches this Collection for the specified object.
boolean	containsAll(Collection<?> collection) Searches this Collection for all objects in the specified Collection.
boolean	isEmpty() Returns true if the collection has no element, otherwise false.
abstract Iterator<E>	iterator() Returns an Iterator on the elements of this Collection.
boolean	remove(Object object) Removes the first occurrence of the specified object from this Collection.
boolean	removeAll(Collection<?> collection) Removes all occurrences in this Collection of each object in the specified Collection.
boolean	retainAll(Collection<?> collection) Removes all objects from this Collection that are not contained in the specified Collection.
abstract int	size() Returns the number of elements in this Collection.
<T> T[]	toArray(T[] contents) Returns an array containing all elements contained in this Collection.
Object[]	toArray() Returns a new array containing all elements contained in this Collection.
String	toString() Returns the string representation of this Collection.

From class java.lang.Object

Object	clone() Returns a new instance of the same class as the receiver, whose slots have been filled in with the values in the slots of the receiver.
boolean	equals(Object o) Compares the argument to the receiver, and returns true if they represent the same object using a class specific comparison.
void	finalize() Called by the virtual machine when there are no longer any (non-weak) references to the receiver.
final Class<? extends Object>	getClass() Returns the unique instance of java.lang.Class which represents the class of the receiver.
int	hashCode() Returns an integer hash code for the receiver.
final void	notify() Causes one thread which is `wait` ing on the receiver to be made ready to run.
final void	notifyAll() Causes all threads which are `wait` ing on the receiver to be made ready to run.
String	toString() Returns a string containing a concise, human-readable description of the receiver.
final void	wait(long time, int frac) Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by `notify` or `notifyAll`) or the expiration of the timeout.
final void	wait(long time) Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by `notify` or `notifyAll`) or the expiration of the timeout.
final void	wait() Causes the thread which sent this message to be made not ready to run pending some change in the receiver (as indicated by `notify` or `notifyAll`).

From interface java.lang.Iterable

From interface java.util.Collection

abstract boolean	add(E object) Attempts to add `object` to the contents of this `Collection`.
abstract boolean	addAll(Collection<? extends E> collection) Attempts to add all of the objects contained in `collection` to the contents of this collection.
abstract void	clear() Removes all elements from this Collection, leaving it empty.
abstract boolean	contains(Object object) Searches this Collection for the specified object.
abstract boolean	containsAll(Collection<?> collection) Searches this Collection for all objects 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 has no elements, a size of zero.
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 the first occurrence of the specified object from this Collection.
abstract boolean	removeAll(Collection<?> collection) Removes all occurrences in this Collection of each object in the specified Collection.
abstract boolean	retainAll(Collection<?> collection) Removes all objects from this Collection that are not also found in the contents of `collection`.
abstract int	size() Returns a count of how many objects are contained by this collection.
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.util.Set

abstract boolean	add(E object) Adds the specified object to this Set.
abstract boolean	addAll(Collection<? extends E> collection) Adds the objects in the specified Collection which do not exist in this Set.
abstract void	clear() Removes all elements from this Set, leaving it empty.
abstract boolean	contains(Object object) Searches this Set for the specified object.
abstract boolean	containsAll(Collection<?> collection) Searches this Set for all objects 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 Set has no elements, a size of zero.
abstract Iterator<E>	iterator() Returns an Iterator on the elements of this Set.
abstract boolean	remove(Object object) Removes any occurrence of the specified object from this Set.
abstract boolean	removeAll(Collection<?> collection) Removes all objects in the specified Collection from this Set.
abstract boolean	retainAll(Collection<?> collection) Removes all objects from this Set that are not contained in the specified Collection.
abstract int	size() Returns the number of elements in this Set.
abstract <T> T[]	toArray(T[] array) Returns an array containing all elements contained in this Set.
abstract Object[]	toArray() Returns an array containing all elements contained in this Set.

Public Constructors

public CopyOnWriteArraySet ()

Creates an empty set.

public CopyOnWriteArraySet (Collection<? extends E> c)

Creates a set containing all of the elements of the specified Collection.

Parameters

c	the collection

Public Methods

public boolean add (E o)

If the specified element is not contained within this collection, and addition of this element succeeds, then true will be returned. If the specified element is already contained within this collection, or duplication is not permitted, false will be returned. Different implementations may add specific limitations on this method to filter permitted elements. For example, in some implementation, null element may be denied, and NullPointerException will be thrown out. These limitations should be explicitly documented by specific collection implementation. Add operation is not supported in this implementation, and UnsupportedOperationException will always be thrown out.

Parameters

o	the element to be added.

Returns

true if the collection is changed successfully after invoking this method. Otherwise, false.

public boolean addAll (Collection<? extends E> c)

Adds the objects in the specified Collection to this Collection.

Parameters

c	the Collection of objects

Returns

true if this Collection is modified, false otherwise

public void clear ()

Removes all the elements in this collection. This collection will be cleared up after this operation. The operation iterates over the collection, removes every element using Iterator.remove method. UnsupportedOperationException will be thrown out if the iterator returned by this collection does not implement the remove method and the collection is not zero length.

public boolean contains (Object o)

Searches this Collection for the specified object.

Parameters

o	the object to search for

Returns

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

public boolean containsAll (Collection<?> c)

Searches this Collection for all objects in the specified Collection.

Parameters

c	the Collection of objects

Returns

true if all objects in the specified Collection are elements of this Collection, false otherwise

public boolean isEmpty ()

Returns true if the collection has no element, otherwise false.

Returns

true if the collection has no element.

public Iterator<E> iterator ()

Returns an Iterator on the elements of this Collection. A subclass must implement the abstract methods iterator() and size().

Returns

an Iterator on the elements of this Collection

public boolean remove (Object o)

Removes the first occurrence of the specified object from this Collection. This operation traverses over the collection, looking for the specified object. Once the object is found, the object will be removed from the collection using the iterator's remove method. This collection will throw an UnsupportedOperationException if the iterator returned does not implement remove method, and the specified object is in this collection.

Parameters

o	the object to remove

Returns

true if this Collection is modified, false otherwise

public boolean removeAll (Collection<?> c)

Removes all occurrences in this Collection of each object in the specified Collection.

Parameters

c	the Collection of objects to remove

Returns

true if this Collection is modified, false otherwise

public boolean retainAll (Collection<?> c)

Removes all objects from this Collection that are not contained in the specified Collection. This operation traverses over the collection itself, to verify whether any element is contained in the specified collection. The object will be removed from the collection itself using the iterator's remove method if it is not contained in the specified collection. This collection will throw an UnsupportedOperationException if the iterator returned does not implement remove method, and the collection itself does contain elements which do not exist in the specified collection.

Parameters

c	the Collection of objects to retain

Returns

true if this Collection is modified, false otherwise

public int size ()

Returns the number of elements in this Collection.

Returns

the number of elements in this Collection

public T[] toArray (T[] a)

Returns an array containing all elements contained in this Collection. 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 Collection, the array element following the collection elements is set to null.

Parameters

a	the array

Returns

an array of the elements from this Collection

public Object[] toArray ()

Returns a new array containing all elements contained in this Collection. All the elements in the array will not be referenced by the collection. The elements in the returned array will be sorted to the same order as those returned by the iterator of this collection itself if the collection guarantees the order.

Returns

an array of the elements from this Collection

Feb	MAR	Apr
	22
2008	2009	2010

Interfaces

Classes

Enums

Exceptions

CopyOnWriteArraySet

Class Overview

See Also

Summary

Public Constructors

public CopyOnWriteArraySet ()

public CopyOnWriteArraySet (Collection<? extends E> c)

Parameters

Public Methods

public boolean add (E o)

Parameters

Returns

public boolean addAll (Collection<? extends E> c)

Parameters

Returns

public void clear ()

public boolean contains (Object o)

Parameters

Returns

public boolean containsAll (Collection<?> c)

Parameters

Returns

public boolean isEmpty ()

Returns

public Iterator<E> iterator ()

Returns

public boolean remove (Object o)

Parameters

Returns

public boolean removeAll (Collection<?> c)

Parameters

Returns

public boolean retainAll (Collection<?> c)

Parameters

Returns

public int size ()

Returns

public T[] toArray (T[] a)

Parameters

Returns

public Object[] toArray ()

Returns