This documentation differs from the official API. Jadeite adds extra features to the API including: variable font sizes, constructions examples, placeholders for classes and methods, and auto-generated “See Also” links. Additionally it is missing some items found in standard Javadoc documentation, including: generics type information, “Deprecated” tags and comments, “See Also” links, along with other minor differences. Please send any questions or feedback to bam@cs.cmu.edu.


java.util.concurrent
class CopyOnWriteArrayList

java.lang.Object extended by java.util.concurrent.CopyOnWriteArrayList
All Implemented Interfaces:
Serializable, Cloneable, List, RandomAccess

Most common way to construct:

CopyOnWriteArrayList empty = new CopyOnWriteArrayList();

Based on 25 examples


public class CopyOnWriteArrayList
extends Object
implements List, RandomAccess, Cloneable, Serializable

A thread-safe variant of {@link java.util.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.

All elements are permitted, including null.

Memory consistency effects: As with other concurrent collections, actions in a thread prior to placing an object into a {@code CopyOnWriteArrayList} happen-before actions subsequent to the access or removal of that element from the {@code CopyOnWriteArrayList} in another thread.

This class is a member of the Java Collections Framework.


Constructor Summary

          Creates an empty list.

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

          Creates a list holding a copy of the given array.
 
Method Summary
 boolean

          Appends the specified element to the end of this list.
 void
add(int index, Object element)

          Inserts the specified element at the specified position in this list.
 boolean

          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 c)

          Inserts all of the elements in the specified collection into this list, starting at the specified position.
 int

          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

          Append the element if not present.
 void

          Removes all of the elements from this list.
 Object

          Returns a shallow copy of this list.
 boolean

          Returns true if this list contains the specified element.
 boolean

          Returns true if this list contains all of the elements of the specified collection.
 boolean

          Compares the specified object with this list for equality.
 Object
get(int index)

          
 int

          Returns the hash code value for this list.
 int
indexOf(Object e, int index)

          Returns the index of the first occurrence of the specified element in this list, searching forwards from index, or returns -1 if the element is not found.
 int

          
 boolean

          Returns true if this list contains no elements.
 Iterator

          Returns an iterator over the elements in this list in proper sequence.
 int
lastIndexOf(Object e, int index)

          Returns the index of the last occurrence of the specified element in this list, searching backwards from index, or returns -1 if the element is not found.
 int

          
 ListIterator

          
 ListIterator
listIterator(int index)

          
 Object
remove(int index)

          Removes the element at the specified position in this list.
 boolean

          Removes the first occurrence of the specified element from this list, if it is present.
 boolean

          Removes from this list all of its elements that are contained in the specified collection.
 boolean

          Retains only the elements in this list that are contained in the specified collection.
 Object
set(int index, Object element)

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

          Returns the number of elements in this list.
 List
subList(int fromIndex, int toIndex)

          Returns a view of the portion of this list between fromIndex, inclusive, and toIndex, exclusive.
 Object[]

          Returns an array containing all of the elements in this list in proper sequence (from first to last element).
 Object[]

          Returns an array containing all of the elements in this list in proper sequence (from first to last element); the runtime type of the returned array is that of the specified array.
 String

          Returns a string representation of this list.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

CopyOnWriteArrayList

public CopyOnWriteArrayList()
Creates an empty list.


CopyOnWriteArrayList

public CopyOnWriteArrayList(Collection 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(Object[] toCopyIn)
Creates a list holding a copy of the given array.

Parameters:
toCopyIn - the array (a copy of this array is used as the internal array)
Method Detail

add

public boolean add(Object e)
Appends the specified element to the end of this list.

Parameters:
e - element to be appended to this list
Returns:
true (as specified by {@link Collection#add})

add

public void add(int index,
                Object 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).

Parameters:
index
element

addAll

public boolean addAll(Collection 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.

Parameters:
c - collection containing elements to be added to this list
Returns:
true if this list changed as a result of the call

addAll

public boolean addAll(int index,
                      Collection c)
Inserts all of the elements in the specified collection into this list, starting at the specified position. Shifts the element currently at that position (if any) and any subsequent elements to the right (increases their indices). The new elements will appear in this list in the order that they are returned by the specified collection's iterator.

Parameters:
index - index at which to insert the first element from the specified collection
c - collection containing elements to be added to this list
Returns:
true if this list changed as a result of the call

addAllAbsent

public int addAllAbsent(Collection 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.

Parameters:
c - collection containing elements to be added to this list
Returns:
the number of elements added

addIfAbsent

public boolean addIfAbsent(Object e)
Append the element if not present.

Parameters:
e - element to be added to this list, if absent
Returns:
true if the element was added

clear

public void clear()
Removes all of the elements from this list. The list will be empty after this call returns.


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

contains

public boolean contains(Object o)
Returns true if this list contains the specified element. More formally, returns true if and only if this list contains at least one element e such that (o==null ? e==null : o.equals(e)).

Parameters:
o - element whose presence in this list is to be tested
Returns:
true if this list contains the specified element

containsAll

public boolean containsAll(Collection c)
Returns true if this list contains all of the elements of the specified collection.

Parameters:
c - collection to be checked for containment in this list
Returns:
true if this list contains all of the elements of the specified collection

equals

public boolean equals(Object o)
Compares the specified object with this list for equality. Returns {@code true} if the specified object is the same object as this object, or if it is also a {@link List} and the sequence of elements returned by an {@linkplain List#iterator() iterator} over the specified list is the same as the sequence returned by an iterator over this list. The two sequences are considered to be the same if they have the same length and corresponding elements at the same position in the sequence are equal. Two elements {@code e1} and {@code e2} are considered equal if {@code (e1==null ? e2==null : e1.equals(e2))}.

Overrides:
equals in class Object
Parameters:
o - the object to be compared for equality with this list
Returns:
{@code true} if the specified object is equal to this list

get

public Object get(int index)
{@inheritDoc}

Parameters:
index

hashCode

public int hashCode()
Returns the hash code value for this list.

This implementation uses the definition in {@link List#hashCode}.

Overrides:
hashCode in class Object
Returns:
the hash code value for this list

indexOf

public int indexOf(Object e,
                   int index)
Returns the index of the first occurrence of the specified element in this list, searching forwards from index, or returns -1 if the element is not found. More formally, returns the lowest index i such that (i >= index && (e==null ? get(i)==null : e.equals(get(i)))), or -1 if there is no such index.

Parameters:
e - element to search for
index - index to start searching from
Returns:
the index of the first occurrence of the element in this list at position index or later in the list; -1 if the element is not found.

indexOf

public int indexOf(Object o)
{@inheritDoc}

Parameters:
o

isEmpty

public boolean isEmpty()
Returns true if this list contains no elements.

Returns:
true if this list contains no elements

iterator

public Iterator iterator()
Returns an iterator over the elements in this list in proper sequence.

The returned iterator provides a snapshot of the state of the list when the iterator was constructed. No synchronization is needed while traversing the iterator. The iterator does NOT support the remove method.

Returns:
an iterator over the elements in this list in proper sequence

lastIndexOf

public int lastIndexOf(Object e,
                       int index)
Returns the index of the last occurrence of the specified element in this list, searching backwards from index, or returns -1 if the element is not found. More formally, returns the highest index i such that (i <= index && (e==null ? get(i)==null : e.equals(get(i)))), or -1 if there is no such index.

Parameters:
e - element to search for
index - index to start searching backwards from
Returns:
the index of the last occurrence of the element at position less than or equal to index in this list; -1 if the element is not found.

lastIndexOf

public int lastIndexOf(Object o)
{@inheritDoc}

Parameters:
o

listIterator

public ListIterator listIterator()
{@inheritDoc}

The returned iterator provides a snapshot of the state of the list when the iterator was constructed. No synchronization is needed while traversing the iterator. The iterator does NOT support the remove, set or add methods.


listIterator

public ListIterator listIterator(int index)
{@inheritDoc}

The returned iterator provides a snapshot of the state of the list when the iterator was constructed. No synchronization is needed while traversing the iterator. The iterator does NOT support the remove, set or add methods.

Parameters:
index

remove

public Object 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). Returns the element that was removed from the list.

Parameters:
index

remove

public boolean remove(Object o)
Removes the first occurrence of the specified element from this list, if it is present. If this list does not contain the element, it is unchanged. More formally, removes the element with the lowest index i such that (o==null ? get(i)==null : o.equals(get(i))) (if such an element exists). Returns true if this list contained the specified element (or equivalently, if this list changed as a result of the call).

Parameters:
o - element to be removed from this list, if present
Returns:
true if this list contained the specified element

removeAll

public boolean removeAll(Collection c)
Removes from this list all of its elements that are contained in the specified collection. This is a particularly expensive operation in this class because of the need for an internal temporary array.

Parameters:
c - collection containing elements to be removed from this list
Returns:
true if this list changed as a result of the call

retainAll

public boolean retainAll(Collection c)
Retains only the elements in this list that are contained in the specified collection. In other words, removes from this list all of its elements that are not contained in the specified collection.

Parameters:
c - collection containing elements to be retained in this list
Returns:
true if this list changed as a result of the call

set

public Object set(int index,
                  Object element)
Replaces the element at the specified position in this list with the specified element.

Parameters:
index
element

size

public int size()
Returns the number of elements in this list.

Returns:
the number of elements in this list

subList

public List subList(int fromIndex,
                    int toIndex)
Returns a view of the portion of this list between fromIndex, inclusive, and toIndex, exclusive. The returned list is backed by this list, so changes in the returned list are reflected in this list, and vice-versa. While mutative operations are supported, they are probably not very useful for CopyOnWriteArrayLists.

The semantics of the list returned by this method become undefined if the backing list (i.e., this list) is structurally modified in any way other than via the returned list. (Structural modifications are those that change the size of the list, or otherwise perturb it in such a fashion that iterations in progress may yield incorrect results.)

Parameters:
fromIndex - low endpoint (inclusive) of the subList
toIndex - high endpoint (exclusive) of the subList
Returns:
a view of the specified range within this list

toArray

public Object[] toArray()
Returns an array containing all of the elements in this list in proper sequence (from first to last element).

The returned array will be "safe" in that no references to it are maintained by this list. (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.

Returns:
an array containing all the elements in this list

toArray

public Object[] toArray(Object[] a)
Returns an array containing all of the elements in this list in proper sequence (from first to last element); 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 this list fits in the specified array with room to spare (i.e., the array has more elements than this list), the element in the array immediately following the end of the list is set to null. (This is useful in determining the length of this list only if the caller knows that this list does not contain any null elements.)

Like the {@link #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 list known to contain only strings. The following code can be used to dump the list 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().

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 all the elements in this list

toString

public String toString()
Returns a string representation of this list. The string representation consists of the string representations of the list's elements in the order they are returned by its iterator, enclosed in square brackets ("[]"). Adjacent elements are separated by the characters ", " (comma and space). Elements are converted to strings as by {@link String#valueOf(Object)}.

Overrides:
toString in class Object
Returns:
a string representation of this list


This documentation differs from the official API. Jadeite adds extra features to the API including: variable font sizes, constructions examples, placeholders for classes and methods, and auto-generated “See Also” links. Additionally it is missing some items found in standard Javadoc documentation, including: generics type information, “Deprecated” tags and comments, “See Also” links, along with other minor differences. Please send any questions or feedback to bam@cs.cmu.edu.
This page displays the Jadeite version of the documention, which is derived from the offical documentation that contains this copyright notice:
Copyright 2008 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.
The official Sun™ documentation can be found here at http://java.sun.com/javase/6/docs/api/.