E
- the type of elements held in this collectionpublic 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 and Description |
---|
CopyOnWriteArrayList()
Creates an empty list.
|
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.
|
CopyOnWriteArrayList(E[] toCopyIn)
Creates a list holding a copy of the given array.
|
Modifier and Type | Method and Description |
---|---|
boolean |
add(E e)
Appends the specified element to the end of this list.
|
void |
add(int index,
E element)
Inserts the specified element at the specified position in this
list.
|
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.
|
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.
|
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.
|
Object |
clone()
Returns a shallow copy of this list.
|
boolean |
contains(Object o)
Returns
true if this list contains the specified element. |
boolean |
containsAll(Collection<?> c)
Returns
true if this list contains all of the elements of the
specified collection. |
boolean |
equals(Object o)
Compares the specified object with this list for equality.
|
void |
forEach(Consumer<? super E> action)
Performs the given action for each element of the
Iterable
until all elements have been processed or the action throws an
exception. |
E |
get(int index)
Returns the element at the specified position in this list.
|
int |
hashCode()
Returns the hash code value for this list.
|
int |
indexOf(E 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 |
indexOf(Object o)
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<E> |
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 from
index , or returns -1 if
the element is not found. |
int |
lastIndexOf(Object o)
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<E> |
listIterator()
Returns a list iterator over the elements in this list (in proper
sequence).
|
ListIterator<E> |
listIterator(int index)
Returns a list iterator over the elements in this list (in proper
sequence), starting at the specified position in the list.
|
E |
remove(int index)
Removes the element at the specified position in this list.
|
boolean |
remove(Object o)
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 |
removeIf(Predicate<? super E> filter)
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.
|
E |
set(int index,
E element)
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 specified
Comparator . |
Spliterator<E> |
spliterator()
Returns a
Spliterator over the elements in this list. |
List<E> |
subList(int fromIndex,
int toIndex)
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(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.
|
String |
toString()
Returns a string representation of this list.
|
finalize, getClass, notify, notifyAll, wait, wait, wait
parallelStream, stream
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
(o==null ? e==null : o.equals(e)).public int indexOf(Object o)
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 && (e==null ? get(i)==null : e.equals(get(i)))),
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)
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 && (e==null ? get(i)==null : e.equals(get(i)))),
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.
toArray
in interface Collection<E>
toArray
in interface List<E>
Arrays.asList(Object[])
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 runtime 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 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 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 boolean remove(Object o)
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).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 nullcontains(Object)
public 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 nullremove(Object)
public 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 nullremove(Object)
public int addAllAbsent(Collection<? extends E> c)
c
- collection containing elements to be added to this listNullPointerException
- if the specified collection is nulladdIfAbsent(Object)
public 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 nulladd(Object)
public 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 nulladd(int,Object)
public void forEach(Consumer<? super E> action)
Iterable
Iterable
until all elements have been processed or the action throws an
exception. Unless otherwise specified by the implementing class,
actions are performed in the order of iteration (if an iteration order
is specified). Exceptions thrown by the action are relayed to the
caller.public 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 removedpublic void replaceAll(UnaryOperator<E> operator)
List
replaceAll
in interface List<E>
operator
- the operator to apply to each elementpublic void sort(Comparator<? super E> c)
List
Comparator
.
All elements in this list must be mutually comparable using the
specified comparator (that is, c.compare(e1, e2)
must not throw
a ClassCastException
for any elements e1
and e2
in the list).
If the specified comparator is null
then all elements in this
list must implement the Comparable
interface and the elements'
natural ordering should be used.
This list must be modifiable, but need not be resizable.
sort
in interface List<E>
c
- the Comparator
used to compare list elements.
A null
value indicates that the elements'
natural ordering should be usedpublic 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 (e1==null ? e2==null : e1.equals(e2))
.equals
in interface Collection<E>
equals
in interface List<E>
equals
in class Object
o
- the object to be compared for equality with this listtrue
if the specified object is equal to this listObject.hashCode()
,
HashMap
public int hashCode()
This implementation uses the definition in List.hashCode()
.
hashCode
in interface Collection<E>
hashCode
in interface List<E>
hashCode
in class Object
Object.equals(java.lang.Object)
,
System.identityHashCode(java.lang.Object)
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 Iterable<E>
spliterator
in interface Collection<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) Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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