E
- the type of elements held in this listSerializable
, Cloneable
, Iterable<E>
, Collection<E>
, List<E>
, RandomAccess
, SequencedCollection<E>
public class CopyOnWriteArrayList<E> extends Object implements List<E>, RandomAccess, Cloneable, Serializable
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 CopyOnWriteArrayList
happen-before actions subsequent to the access or removal of that element from the CopyOnWriteArrayList
in another thread.
This class is a member of the Java Collections Framework.
Constructor | Description |
---|---|
CopyOnWriteArrayList() |
Creates an empty list. |
CopyOnWriteArrayList |
Creates a list holding a copy of the given array. |
CopyOnWriteArrayList |
Creates a list containing the elements of the specified collection, in the order they are returned by the collection's iterator. |
Modifier and Type | Method | Description |
---|---|---|
void |
add |
Inserts the specified element at the specified position in this list. |
boolean |
add |
Appends the specified element to the end of this list. |
boolean |
addAll |
Inserts all of the elements in the specified collection into this list, starting at the specified position. |
boolean |
addAll |
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. |
int |
addAllAbsent |
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. |
void |
addFirst |
Adds an element as the first element of this collection (optional operation). |
boolean |
addIfAbsent |
Appends the element, if not present. |
void |
addLast |
Adds an element as the last element of this collection (optional operation). |
void |
clear() |
Removes all of the elements from this list. |
Object |
clone() |
Returns a shallow copy of this list. |
boolean |
contains |
Returns true if this list contains the specified element. |
boolean |
containsAll |
Returns true if this list contains all of the elements of the specified collection. |
boolean |
equals |
Compares the specified object with this list for equality. |
void |
forEach |
Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception. |
E |
get |
Returns the element at the specified position in this list. |
E |
getFirst() |
Gets the first element of this collection. |
E |
getLast() |
Gets the last element of this collection. |
int |
hashCode() |
Returns the hash code value for this list. |
int |
indexOf |
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 |
indexOf |
Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element. |
boolean |
isEmpty() |
Returns true if this list contains no elements. |
Iterator |
iterator() |
Returns an iterator over the elements in this list in proper sequence. |
int |
lastIndexOf |
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 |
lastIndexOf |
Returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element. |
ListIterator |
listIterator() |
Returns a list iterator over the elements in this list (in proper sequence). |
ListIterator |
listIterator |
Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list. |
E |
remove |
Removes the element at the specified position in this list. |
boolean |
remove |
Removes the first occurrence of the specified element from this list, if it is present. |
boolean |
removeAll |
Removes from this list all of its elements that are contained in the specified collection. |
E |
removeFirst() |
Removes and returns the first element of this collection (optional operation). |
boolean |
removeIf |
Removes all of the elements of this collection that satisfy the given predicate. |
E |
removeLast() |
Removes and returns the last element of this collection (optional operation). |
boolean |
retainAll |
Retains only the elements in this list that are contained in the specified collection. |
List |
reversed() |
Returns a reverse-ordered view of this collection. |
E |
set |
Replaces the element at the specified position in this list with the specified element. |
int |
size() |
Returns the number of elements in this list. |
Spliterator |
spliterator() |
Returns a Spliterator over the elements in this list. |
List |
subList |
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 proper sequence (from first to last element). |
<T> T[] |
toArray |
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 |
toString() |
Returns a string representation of this list. |
parallelStream, stream, toArray
replaceAll, sort
public CopyOnWriteArrayList()
public CopyOnWriteArrayList(Collection<? extends E> c)
c
- the collection of initially held elementsNullPointerException
- if the specified collection is nullpublic CopyOnWriteArrayList(E[] toCopyIn)
toCopyIn
- the array (a copy of this array is used as the internal array)NullPointerException
- if the specified array is nullpublic int size()
public boolean isEmpty()
true
if this list contains no elements.public boolean contains(Object o)
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 Objects.equals(o, e)
.public int indexOf(Object o)
i
such that Objects.equals(o, get(i))
, or -1 if there is no such index.public int indexOf(E e, int index)
index
, or returns -1 if the element is not found. More formally, returns the lowest index i
such that i >= index && Objects.equals(get(i), e)
, or -1 if there is no such index.e
- element to search forindex
- index to start searching fromindex
or later in the list; -1
if the element is not found.IndexOutOfBoundsException
- if the specified index is negativepublic int lastIndexOf(Object o)
i
such that Objects.equals(o, get(i))
, or -1 if there is no such index.lastIndexOf
in interface List<E>
o
- element to search forpublic int lastIndexOf(E e, int index)
index
, or returns -1 if the element is not found. More formally, returns the highest index i
such that i <= index && Objects.equals(get(i), e)
, or -1 if there is no such index.e
- element to search forindex
- index to start searching backwards fromindex
in this list; -1 if the element is not found.IndexOutOfBoundsException
- if the specified index is greater than or equal to the current size of this listpublic Object clone()
public Object[] toArray()
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.
public <T> T[] toArray(T[] a)
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 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()
.toArray
in interface Collection<E>
toArray
in interface List<E>
T
- the component type of the array to contain the collectiona
- 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.ArrayStoreException
- if the runtime type of the specified array is not a supertype of the runtime type of every element in this listNullPointerException
- if the specified array is nullpublic E get(int index)
get
in interface List<E>
index
- index of the element to returnIndexOutOfBoundsException
- if the index is out of range (index < 0 || index >= size()
)public E getFirst()
getFirst
in interface List<E>
getFirst
in interface SequencedCollection<E>
NoSuchElementException
- if this collection is emptypublic E getLast()
getLast
in interface List<E>
getLast
in interface SequencedCollection<E>
NoSuchElementException
- if this collection is emptypublic E set(int index, E element)
set
in interface List<E>
index
- index of the element to replaceelement
- element to be stored at the specified positionIndexOutOfBoundsException
- if the index is out of range (index < 0 || index >= size()
)public boolean add(E e)
add
in interface Collection<E>
add
in interface List<E>
e
- element to be appended to this listtrue
(as specified by Collection.add(E)
)public void add(int index, E element)
add
in interface List<E>
index
- index at which the specified element is to be insertedelement
- element to be insertedIndexOutOfBoundsException
- if the index is out of range (index < 0 || index > size()
)public void addFirst(E e)
public void addLast(E e)
public E remove(int index)
remove
in interface List<E>
index
- the index of the element to be removedIndexOutOfBoundsException
- if the index is out of range (index < 0 || index >= size()
)public E removeFirst()
removeFirst
in interface List<E>
removeFirst
in interface SequencedCollection<E>
NoSuchElementException
- if this collection is emptypublic E removeLast()
removeLast
in interface List<E>
removeLast
in interface SequencedCollection<E>
NoSuchElementException
- if this collection is emptypublic boolean remove(Object o)
i
such that Objects.equals(o, 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).public boolean addIfAbsent(E e)
e
- element to be added to this list, if absenttrue
if the element was addedpublic boolean containsAll(Collection<?> c)
true
if this list contains all of the elements of the specified collection.containsAll
in interface Collection<E>
containsAll
in interface List<E>
c
- collection to be checked for containment in this listtrue
if this list contains all of the elements of the specified collectionNullPointerException
- if the specified collection is nullpublic boolean removeAll(Collection<?> c)
removeAll
in interface Collection<E>
removeAll
in interface List<E>
c
- collection containing elements to be removed from this listtrue
if this list changed as a result of the callClassCastException
- if the class of an element of this list is incompatible with the specified collection (optional)NullPointerException
- if this list contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is nullpublic boolean retainAll(Collection<?> c)
retainAll
in interface Collection<E>
retainAll
in interface List<E>
c
- collection containing elements to be retained in this listtrue
if this list changed as a result of the callClassCastException
- if the class of an element of this list is incompatible with the specified collection (optional)NullPointerException
- if this list contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is nullpublic int addAllAbsent(Collection<? extends E> c)
c
- collection containing elements to be added to this listNullPointerException
- if the specified collection is nullpublic void clear()
public boolean addAll(Collection<? extends E> c)
addAll
in interface Collection<E>
addAll
in interface List<E>
c
- collection containing elements to be added to this listtrue
if this list changed as a result of the callNullPointerException
- if the specified collection is nullpublic boolean addAll(int index, Collection<? extends E> c)
addAll
in interface List<E>
index
- index at which to insert the first element from the specified collectionc
- collection containing elements to be added to this listtrue
if this list changed as a result of the callIndexOutOfBoundsException
- if the index is out of range (index < 0 || index > size()
)NullPointerException
- if the specified collection is nullpublic void forEach(Consumer<? super E> action)
Iterable
Iterable
until all elements have been processed or the action throws an exception. Actions are performed in the order of iteration, if that order is specified. Exceptions thrown by the action are relayed to the caller. The behavior of this method is unspecified if the action performs side-effects that modify the underlying source of elements, unless an overriding class has specified a concurrent modification policy.
forEach
in interface Iterable<E>
action
- The action to be performed for each elementNullPointerException
- if the specified action is nullpublic boolean removeIf(Predicate<? super E> filter)
Collection
removeIf
in interface Collection<E>
filter
- a predicate which returns true
for elements to be removedtrue
if any elements were removedNullPointerException
- if the specified filter is nullpublic String toString()
"[]"
). Adjacent elements are separated by the characters ", "
(comma and space). Elements are converted to strings as by String.valueOf(Object)
.public boolean equals(Object o)
true
if the specified object is the same object as this object, or if it is also a List
and the sequence of elements returned by an 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 e1
and e2
are considered equal if Objects.equals(e1, e2)
.public int hashCode()
This implementation uses the definition in List.hashCode()
.
public Iterator<E> iterator()
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.
public ListIterator<E> listIterator()
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
in interface List<E>
public ListIterator<E> listIterator(int index)
next
. An initial call to previous
would return the element with the specified index minus one. 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
in interface List<E>
index
- index of the first element to be returned from the list iterator (by a call to next
)IndexOutOfBoundsException
- if the index is out of range (index < 0 || index > size()
)public Spliterator<E> spliterator()
Spliterator
over the elements in this list. The Spliterator
reports Spliterator.IMMUTABLE
, Spliterator.ORDERED
, Spliterator.SIZED
, and Spliterator.SUBSIZED
.
The spliterator provides a snapshot of the state of the list when the spliterator was constructed. No synchronization is needed while operating on the spliterator.
spliterator
in interface Collection<E>
spliterator
in interface Iterable<E>
spliterator
in interface List<E>
Spliterator
over the elements in this listpublic List<E> subList(int fromIndex, int toIndex)
fromIndex
, inclusive, and toIndex
, exclusive. The returned list is backed by this list, so changes in the returned list are reflected in this list. The semantics of the list returned by this method become undefined if the backing list (i.e., this list) is modified in any way other than via the returned list.
subList
in interface List<E>
fromIndex
- low endpoint (inclusive) of the subListtoIndex
- high endpoint (exclusive) of the subListIndexOutOfBoundsException
- for an illegal endpoint index value (fromIndex < 0 || toIndex > size ||
fromIndex > toIndex
)public List<E> reversed()
Modifications to the reversed view are permitted and will be propagated to this list. In addition, modifications to this list will be visible in the reversed view. Sublists and iterators of the reversed view have the same restrictions as those of this list.
© 1993, 2023, Oracle and/or its affiliates. All rights reserved.
Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.
https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/concurrent/CopyOnWriteArrayList.html