- Type Parameters:
E
- the type of elements held in this list
- All Implemented Interfaces:
Serializable
,Cloneable
,Iterable<E>
,Collection<E>
,List<E>
,RandomAccess
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.
- Since:
- 1.5
- See Also:
-
Constructor Summary
ConstructorDescriptionCreates an empty list.CopyOnWriteArrayList
(E[] toCopyIn) Creates a list holding a copy of the given array.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. -
Method Summary
Modifier and TypeMethodDescriptionvoid
Inserts the specified element at the specified position in this list.boolean
Appends the specified element to the end of this list.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.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.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 e) Appends the element, if not present.void
clear()
Removes all of the elements from this list.clone()
Returns a shallow copy of this list.boolean
Returnstrue
if this list contains the specified element.boolean
containsAll
(Collection<?> c) Returnstrue
if this list contains all of the elements of the specified collection.boolean
Compares the specified object with this list for equality.void
Performs the given action for each element of theIterable
until all elements have been processed or the action throws an exception.get
(int index) Returns the element at the specified position in this list.int
hashCode()
Returns the hash code value for this list.int
Returns the index of the first occurrence of the specified element in this list, searching forwards fromindex
, or returns -1 if the element is not found.int
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()
Returnstrue
if this list contains no elements.iterator()
Returns an iterator over the elements in this list in proper sequence.int
lastIndexOf
(E e, int index) Returns the index of the last occurrence of the specified element in this list, searching backwards fromindex
, or returns -1 if the element is not found.int
Returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element.Returns a list iterator over the elements in this list (in proper sequence).listIterator
(int index) Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list.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
removeAll
(Collection<?> c) Removes from this list all of its elements that are contained in the specified collection.boolean
Removes all of the elements of this collection that satisfy the given predicate.void
replaceAll
(UnaryOperator<E> operator) Replaces each element of this list with the result of applying the operator to that element.boolean
retainAll
(Collection<?> c) Retains only the elements in this list that are contained in the specified collection.Replaces the element at the specified position in this list with the specified element.int
size()
Returns the number of elements in this list.void
sort
(Comparator<? super E> c) Sorts this list according to the order induced by the specifiedComparator
.Returns aSpliterator
over the elements in this list.subList
(int fromIndex, int toIndex) Returns a view of the portion of this list betweenfromIndex
, inclusive, andtoIndex
, 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
(T[] 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.toString()
Returns a string representation of this list.Methods inherited from class java.lang.Object
finalize, getClass, notify, notifyAll, wait, wait, wait
Methods inherited from interface java.util.Collection
parallelStream, stream, toArray
-
Constructor Details
-
CopyOnWriteArrayList
public CopyOnWriteArrayList()Creates an empty list. -
CopyOnWriteArrayList
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- Throws:
NullPointerException
- if the specified collection is null
-
CopyOnWriteArrayList
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)- Throws:
NullPointerException
- if the specified array is null
-
-
Method Details
-
size
public int size()Returns the number of elements in this list. -
isEmpty
public boolean isEmpty()Returnstrue
if this list contains no elements. -
contains
Returnstrue
if this list contains the specified element. More formally, returnstrue
if and only if this list contains at least one elemente
such thatObjects.equals(o, e)
. -
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. More formally, returns the lowest indexi
such thatObjects.equals(o, get(i))
, or -1 if there is no such index. -
indexOf
Returns the index of the first occurrence of the specified element in this list, searching forwards fromindex
, or returns -1 if the element is not found. More formally, returns the lowest indexi
such thati >= index && Objects.equals(get(i), e)
, or -1 if there is no such index.- Parameters:
e
- element to search forindex
- 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. - Throws:
IndexOutOfBoundsException
- if the specified index is negative
-
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. More formally, returns the highest indexi
such thatObjects.equals(o, get(i))
, or -1 if there is no such index.- Specified by:
lastIndexOf
in interfaceList<E>
- Parameters:
o
- element to search for- Returns:
- the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element
-
lastIndexOf
Returns the index of the last occurrence of the specified element in this list, searching backwards fromindex
, or returns -1 if the element is not found. More formally, returns the highest indexi
such thati <= index && Objects.equals(get(i), e)
, or -1 if there is no such index.- Parameters:
e
- element to search forindex
- 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. - Throws:
IndexOutOfBoundsException
- if the specified index is greater than or equal to the current size of this list
-
clone
Returns a shallow copy of this list. (The elements themselves are not copied.) -
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.
-
toArray
public <T> T[] toArray(T[] 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
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 ofString
:String[] y = x.toArray(new String[0]);
toArray(new Object[0])
is identical in function totoArray()
.- Specified by:
toArray
in interfaceCollection<E>
- Specified by:
toArray
in interfaceList<E>
- Type Parameters:
T
- the component type of the array to contain the collection- 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
- Throws:
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 null
-
get
Returns the element at the specified position in this list.- Specified by:
get
in interfaceList<E>
- Parameters:
index
- index of the element to return- Returns:
- the element at the specified position in this list
- Throws:
IndexOutOfBoundsException
- if the index is out of range (index < 0 || index >= size()
)
-
set
Replaces the element at the specified position in this list with the specified element.- Specified by:
set
in interfaceList<E>
- Parameters:
index
- index of the element to replaceelement
- element to be stored at the specified position- Returns:
- the element previously at the specified position
- Throws:
IndexOutOfBoundsException
- if the index is out of range (index < 0 || index >= size()
)
-
add
Appends the specified element to the end of this list.- Specified by:
add
in interfaceCollection<E>
- Specified by:
add
in interfaceList<E>
- Parameters:
e
- element to be appended to this list- Returns:
true
(as specified byCollection.add(E)
)
-
add
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 interfaceList<E>
- Parameters:
index
- index at which the specified element is to be insertedelement
- element to be inserted- Throws:
IndexOutOfBoundsException
- if the index is out of range (index < 0 || index > size()
)
-
remove
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.- Specified by:
remove
in interfaceList<E>
- Parameters:
index
- the index of the element to be removed- Returns:
- the element previously at the specified position
- Throws:
IndexOutOfBoundsException
- if the index is out of range (index < 0 || index >= size()
)
-
remove
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 indexi
such thatObjects.equals(o, get(i))
(if such an element exists). Returnstrue
if this list contained the specified element (or equivalently, if this list changed as a result of the call). -
addIfAbsent
Appends the element, if not present.- Parameters:
e
- element to be added to this list, if absent- Returns:
true
if the element was added
-
containsAll
Returnstrue
if this list contains all of the elements of the specified collection.- Specified by:
containsAll
in interfaceCollection<E>
- Specified by:
containsAll
in interfaceList<E>
- 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- Throws:
NullPointerException
- if the specified collection is null- See Also:
-
removeAll
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.- Specified by:
removeAll
in interfaceCollection<E>
- Specified by:
removeAll
in interfaceList<E>
- Parameters:
c
- collection containing elements to be removed from this list- Returns:
true
if this list changed as a result of the call- Throws:
ClassCastException
- 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 null- See Also:
-
retainAll
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.- Specified by:
retainAll
in interfaceCollection<E>
- Specified by:
retainAll
in interfaceList<E>
- Parameters:
c
- collection containing elements to be retained in this list- Returns:
true
if this list changed as a result of the call- Throws:
ClassCastException
- 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 null- See Also:
-
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.- Parameters:
c
- collection containing elements to be added to this list- Returns:
- the number of elements added
- Throws:
NullPointerException
- if the specified collection is null- See Also:
-
clear
public void clear()Removes all of the elements from this list. The list will be empty after this call returns. -
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.- Specified by:
addAll
in interfaceCollection<E>
- Specified by:
addAll
in interfaceList<E>
- Parameters:
c
- collection containing elements to be added to this list- Returns:
true
if this list changed as a result of the call- Throws:
NullPointerException
- if the specified collection is null- See Also:
-
addAll
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.- Specified by:
addAll
in interfaceList<E>
- Parameters:
index
- index at which to insert the first element from the specified collectionc
- collection containing elements to be added to this list- Returns:
true
if this list changed as a result of the call- Throws:
IndexOutOfBoundsException
- if the index is out of range (index < 0 || index > size()
)NullPointerException
- if the specified collection is null- See Also:
-
forEach
Description copied from interface:Iterable
Performs the given action for each element of theIterable
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.
- Specified by:
forEach
in interfaceIterable<E>
- Parameters:
action
- The action to be performed for each element- Throws:
NullPointerException
- if the specified action is null
-
removeIf
Description copied from interface:Collection
Removes all of the elements of this collection that satisfy the given predicate. Errors or runtime exceptions thrown during iteration or by the predicate are relayed to the caller.- Specified by:
removeIf
in interfaceCollection<E>
- Parameters:
filter
- a predicate which returnstrue
for elements to be removed- Returns:
true
if any elements were removed- Throws:
NullPointerException
- if the specified filter is null
-
replaceAll
Description copied from interface:List
Replaces each element of this list with the result of applying the operator to that element. Errors or runtime exceptions thrown by the operator are relayed to the caller.- Specified by:
replaceAll
in interfaceList<E>
- Parameters:
operator
- the operator to apply to each element
-
sort
Description copied from interface:List
Sorts this list according to the order induced by the specifiedComparator
. The sort is stable: this method must not reorder equal elements.All elements in this list must be mutually comparable using the specified comparator (that is,
c.compare(e1, e2)
must not throw aClassCastException
for any elementse1
ande2
in the list).If the specified comparator is
null
then all elements in this list must implement theComparable
interface and the elements' natural ordering should be used.This list must be modifiable, but need not be resizable.
- Specified by:
sort
in interfaceList<E>
- Parameters:
c
- theComparator
used to compare list elements. Anull
value indicates that the elements' natural ordering should be used
-
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 byString.valueOf(Object)
. -
equals
Compares the specified object with this list for equality. Returnstrue
if the specified object is the same object as this object, or if it is also aList
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 elementse1
ande2
are considered equal ifObjects.equals(e1, e2)
. -
hashCode
public int hashCode()Returns the hash code value for this list.This implementation uses the definition in
List.hashCode()
. -
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. -
listIterator
Returns a list 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
,set
oradd
methods.- Specified by:
listIterator
in interfaceList<E>
- Returns:
- a list iterator over the elements in this list (in proper sequence)
-
listIterator
Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list. The specified index indicates the first element that would be returned by an initial call tonext
. An initial call toprevious
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
oradd
methods.- Specified by:
listIterator
in interfaceList<E>
- Parameters:
index
- index of the first element to be returned from the list iterator (by a call tonext
)- Returns:
- a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list
- Throws:
IndexOutOfBoundsException
- if the index is out of range (index < 0 || index > size()
)
-
spliterator
Returns aSpliterator
over the elements in this list.The
Spliterator
reportsSpliterator.IMMUTABLE
,Spliterator.ORDERED
,Spliterator.SIZED
, andSpliterator.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.
- Specified by:
spliterator
in interfaceCollection<E>
- Specified by:
spliterator
in interfaceIterable<E>
- Specified by:
spliterator
in interfaceList<E>
- Returns:
- a
Spliterator
over the elements in this list - Since:
- 1.8
-
subList
Returns a view of the portion of this list betweenfromIndex
, inclusive, andtoIndex
, 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.
- Specified by:
subList
in interfaceList<E>
- Parameters:
fromIndex
- low endpoint (inclusive) of the subListtoIndex
- high endpoint (exclusive) of the subList- Returns:
- a view of the specified range within this list
- Throws:
IndexOutOfBoundsException
- for an illegal endpoint index value (fromIndex < 0 || toIndex > size || fromIndex > toIndex
)
-