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)
Append 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.
|
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 |
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.
|
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.
|
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()
public boolean contains(Object o)
public int indexOf(Object o)
public int indexOf(E e, int index)
e - element to search forindex - index to start searching fromIndexOutOfBoundsException - 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)
e - element to search forindex - index to start searching backwards fromIndexOutOfBoundsException - 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>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.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 listCollection.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)
public boolean addIfAbsent(E e)
e - element to be added to this list, if absentpublic boolean containsAll(Collection<?> c)
containsAll in interface Collection<E>containsAll in interface List<E>c - collection to be checked for containment in this listNullPointerException - 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 listClassCastException - 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 listClassCastException - 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 listNullPointerException - 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 listIndexOutOfBoundsException - if the index is out of range
(index < 0 || index > size())NullPointerException - if the specified collection is nulladd(int,Object)public String toString()
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 Objecto - the object to be compared for equality with this listtrue if the specified object is equal to this listObject.hashCode(),
HashMappublic int hashCode()
This implementation uses the definition in List.hashCode().
hashCode in interface Collection<E>hashCode in interface List<E>hashCode in class ObjectObject.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 List<E> subList(int fromIndex, int toIndex)
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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