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java.util.concurrent
Class CopyOnWriteArrayList<E>
java.lang.Object
java.util.concurrent.CopyOnWriteArrayList<E>
-
-
Type Parameters:
-
E - the type of elements held in this collection
-
All Implemented Interfaces:
-
Serializable
,
Cloneable
,
Iterable
<E>,
Collection
<E>,
List
<E>,
RandomAccess
-
public class CopyOnWriteArrayList<E>
- extends Object
- implements List<E>, RandomAccess, Cloneable, Serializable
A thread-safe variant of
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
Java Collections Framework
.
-
Since:
-
1.5
-
See Also:
-
Serialized Form
Method Summary
|
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 of the elements in this list (in proper sequence), starting at the specified position in this 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). |
|
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. |
CopyOnWriteArrayList
public CopyOnWriteArrayList()
-
Creates an empty list.
CopyOnWriteArrayList
public 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.
-
Parameters:
-
c - the collection of initially held elements
-
Throws:
-
NullPointerException
- if the specified collection is null
CopyOnWriteArrayList
public CopyOnWriteArrayList(E[] 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)
-
Throws:
-
NullPointerException
- if the specified array is null
size
public int size()
-
Returns the number of elements in this list.
-
-
Specified by:
-
size
in interface
Collection
<
E
>
-
Specified by:
-
size
in interface
List
<
E
>
-
-
Returns:
-
the number of elements in this list
isEmpty
public boolean isEmpty()
-
Returns
true
if this list contains no elements.
-
-
Specified by:
-
isEmpty
in interface
Collection
<
E
>
-
Specified by:
-
isEmpty
in interface
List
<
E
>
-
-
Returns:
-
true
if this list contains no elements
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))
.
-
-
Specified by:
-
contains
in interface
Collection
<
E
>
-
Specified by:
-
contains
in interface
List
<
E
>
-
-
Parameters:
-
o - element whose presence in this list is to be tested
-
Returns:
-
true
if this list contains the specified element
indexOf
public 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. More formally, returns the lowest index
i
such that
(o==null ? get(i)==null : o.equals(get(i)))
, or -1 if there is no such index.
-
-
Specified by:
-
indexOf
in interface
List
<
E
>
-
-
Parameters:
-
o - element to search for
-
Returns:
-
the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element
indexOf
public 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. 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.
-
Throws:
-
IndexOutOfBoundsException
- if the specified index is negative
lastIndexOf
public 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. More formally, returns the highest index
i
such that
(o==null ? get(i)==null : o.equals(get(i)))
, or -1 if there is no such index.
-
-
Specified by:
-
lastIndexOf
in interface
List
<
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
public 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. 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.
-
Throws:
-
IndexOutOfBoundsException
- if the specified index is greater than or equal to the current size of this list
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
-
See Also:
-
Cloneable
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.
-
-
Specified by:
-
toArray
in interface
Collection
<
E
>
-
Specified by:
-
toArray
in interface
List
<
E
>
-
-
Returns:
-
an array containing all the elements in this list
-
See Also:
-
Arrays.asList(Object[])
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 of
String
:
String[] y = x.toArray(new String[0]);
Note that
toArray(new Object[0])
is identical in function to
toArray()
.
-
-
Specified by:
-
toArray
in interface
Collection
<
E
>
-
Specified by:
-
toArray
in interface
List
<
E
>
-
-
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 list
-
NullPointerException
- if the specified array is null
get
public E get(int index)
-
Returns the element at the specified position in this list.
-
-
Specified by:
-
get
in interface
List
<
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
public E set(int index,
E element)
-
Replaces the element at the specified position in this list with the specified element.
-
-
Specified by:
-
set
in interface
List
<
E
>
-
-
Parameters:
-
index - index of the element to replace
-
element - 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
public boolean add(E e)
-
Appends the specified element to the end of this list.
-
-
Specified by:
-
add
in interface
Collection
<
E
>
-
Specified by:
-
add
in interface
List
<
E
>
-
-
Parameters:
-
e - element to be appended to this list
-
Returns:
-
true
(as specified by
Collection.add(E)
)
add
public void add(int index,
E 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).
-
-
Specified by:
-
add
in interface
List
<
E
>
-
-
Parameters:
-
index - index at which the specified element is to be inserted
-
element - element to be inserted
-
Throws:
-
IndexOutOfBoundsException
- if the index is out of range (
index < 0 || index > size()
)
remove
public E 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.
-
-
Specified by:
-
remove
in interface
List
<
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
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).
-
-
Specified by:
-
remove
in interface
Collection
<
E
>
-
Specified by:
-
remove
in interface
List
<
E
>
-
-
Parameters:
-
o - element to be removed from this list, if present
-
Returns:
-
true
if this list contained the specified element
addIfAbsent
public boolean addIfAbsent(E 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
containsAll
public boolean containsAll(Collection<?> c)
-
Returns
true
if this list contains all of the elements of the specified collection.
-
-
Specified by:
-
containsAll
in interface
Collection
<
E
>
-
Specified by:
-
containsAll
in interface
List
<
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:
-
contains(Object)
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.
-
-
Specified by:
-
removeAll
in interface
Collection
<
E
>
-
Specified by:
-
removeAll
in interface
List
<
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:
-
remove(Object)
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.
-
-
Specified by:
-
retainAll
in interface
Collection
<
E
>
-
Specified by:
-
retainAll
in interface
List
<
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:
-
remove(Object)
addAllAbsent
public 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.
-
-
-
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:
-
addIfAbsent(Object)
clear
public void clear()
-
Removes all of the elements from this list. The list will be empty after this call returns.
-
-
Specified by:
-
clear
in interface
Collection
<
E
>
-
Specified by:
-
clear
in interface
List
<
E
>
-
addAll
public 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.
-
-
Specified by:
-
addAll
in interface
Collection
<
E
>
-
Specified by:
-
addAll
in interface
List
<
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:
-
add(Object)
addAll
public 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. 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 interface
List
<
E
>
-
-
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
-
Throws:
-
IndexOutOfBoundsException
- if the index is out of range (
index < 0 || index > size()
)
-
NullPointerException
- if the specified collection is null
-
See Also:
-
add(int,Object)
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
String.valueOf(Object)
.
-
-
Overrides:
-
toString
in class
Object
-
-
Returns:
-
a string representation of this list
equals
public boolean equals(Object o)
-
Compares the specified object with this list for equality. Returns true if
and only 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)).
, both lists have the same size, and all corresponding pairs of elements in the two lists are equal. (Two elements
e1
and
e2
are equal if
(e1==null ? e2==null : e1.equals(e2))
.) In other words, two lists are defined to be equal if they contain the same elements in the same order.
-
-
Specified by:
-
equals
in interface
Collection
<
E
>
-
Specified by:
-
equals
in interface
List
<
E
>
-
Overrides:
-
equals
in class
Object
-
-
Parameters:
-
o - the object to be compared for equality with this list
-
Returns:
-
true
if the specified object is equal to this list
-
See Also:
-
Object.hashCode()
,
Hashtable
hashCode
public int hashCode()
-
Returns the hash code value for this list.
This implementation uses the definition in
List.hashCode()
.
-
-
Specified by:
-
hashCode
in interface
Collection
<
E
>
-
Specified by:
-
hashCode
in interface
List
<
E
>
-
Overrides:
-
hashCode
in class
Object
-
-
Returns:
-
the hash code value for this list
-
See Also:
-
Object.equals(java.lang.Object)
,
Hashtable
iterator
public Iterator<E> 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.
-
-
Specified by:
-
iterator
in interface
Iterable
<
E
>
-
Specified by:
-
iterator
in interface
Collection
<
E
>
-
Specified by:
-
iterator
in interface
List
<
E
>
-
-
Returns:
-
an iterator over the elements in this list in proper sequence
listIterator
public ListIterator<E> 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
or
add
methods.
-
-
Specified by:
-
listIterator
in interface
List
<
E
>
-
-
Returns:
-
a list iterator over the elements in this list (in proper sequence)
listIterator
public ListIterator<E> listIterator(int index)
-
Returns a list iterator of the elements in this list (in proper sequence), starting at the specified position in this list. The specified index indicates the first element that would be returned by an initial call to
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.
-
-
Specified by:
-
listIterator
in interface
List
<
E
>
-
-
Parameters:
-
index - index of first element to be returned from the list iterator (by a call to the
next
method)
-
Returns:
-
a list iterator of the elements in this list (in proper sequence), starting at the specified position in this list
-
Throws:
-
IndexOutOfBoundsException
- if the index is out of range (
index < 0 || index > size()
)
subList
public List<E> 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.)
-
-
Specified by:
-
subList
in interface
List
<
E
>
-
-
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
-
Throws:
-
IndexOutOfBoundsException
- for an illegal endpoint index value (
fromIndex < 0 || toIndex > size || fromIndex > toIndex
)