- Type Parameters:
E- the type of elements held in this list
- All Implemented Interfaces:
Serializable,Cloneable,Iterable<E>,Collection<E>,List<E>,RandomAccess,SequencedCollection<E>
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:
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Constructor Summary
ConstructorsConstructorDescriptionCreates 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 TypeMethodDescriptionvoidInserts the specified element at the specified position in this list.booleanAppends the specified element to the end of this list.booleanaddAll(int index, Collection<? extends E> c) Inserts all of the elements in the specified collection into this list, starting at the specified position.booleanaddAll(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.intaddAllAbsent(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.voidAdds an element as the first element of this collection (optional operation).booleanaddIfAbsent(E e) Appends the element, if not present.voidAdds an element as the last element of this collection (optional operation).voidclear()Removes all of the elements from this list.clone()Returns a shallow copy of this list.booleanReturnstrueif this list contains the specified element.booleancontainsAll(Collection<?> c) Returnstrueif this list contains all of the elements of the specified collection.booleanCompares the specified object with this list for equality.voidPerforms the given action for each element of theIterableuntil all elements have been processed or the action throws an exception.get(int index) Returns the element at the specified position in this list.getFirst()Gets the first element of this collection.getLast()Gets the last element of this collection.inthashCode()Returns the hash code value for this list.intReturns 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.intReturns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element.booleanisEmpty()Returnstrueif this list contains no elements.iterator()Returns an iterator over the elements in this list in proper sequence.intlastIndexOf(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.intReturns 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.booleanRemoves the first occurrence of the specified element from this list, if it is present.booleanremoveAll(Collection<?> c) Removes from this list all of its elements that are contained in the specified collection.Removes and returns the first element of this collection (optional operation).booleanRemoves all of the elements of this collection that satisfy the given predicate.Removes and returns the last element of this collection (optional operation).booleanretainAll(Collection<?> c) Retains only the elements in this list that are contained in the specified collection.reversed()Returns a reverse-ordered view of this collection.Replaces the element at the specified position in this list with the specified element.intsize()Returns the number of elements in this list.Returns aSpliteratorover 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 declared in interface java.util.Collection
parallelStream, stream, toArrayMethods declared in interface java.util.List
replaceAll, sort
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Constructor Details
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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
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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
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Method Details
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size
public int size()Returns the number of elements in this list. -
isEmpty
public boolean isEmpty()Returnstrueif this list contains no elements. -
contains
Returnstrueif this list contains the specified element. More formally, returnstrueif and only if this list contains at least one elementesuch 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 indexisuch 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 indexisuch 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
indexor later in the list;-1if the element is not found. - Throws:
IndexOutOfBoundsException- if the specified index is negative
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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 indexisuch thatObjects.equals(o, get(i)), or -1 if there is no such index.- Specified by:
lastIndexOfin 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
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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 indexisuch 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
indexin 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
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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.
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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
xis a list known to contain only strings. The following code can be used to dump the list into a newly allocated array ofString:
Note thatString[] y = x.toArray(new String[0]);toArray(new Object[0])is identical in function totoArray().- Specified by:
toArrayin interfaceCollection<E>- Specified by:
toArrayin 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
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get
Returns the element at the specified position in this list.- Specified by:
getin 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())
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getFirst
Gets the first element of this collection.- Specified by:
getFirstin interfaceList<E>- Specified by:
getFirstin interfaceSequencedCollection<E>- Returns:
- the retrieved element
- Throws:
NoSuchElementException- if this collection is empty- Since:
- 21
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getLast
Gets the last element of this collection.- Specified by:
getLastin interfaceList<E>- Specified by:
getLastin interfaceSequencedCollection<E>- Returns:
- the retrieved element
- Throws:
NoSuchElementException- if this collection is empty- Since:
- 21
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set
Replaces the element at the specified position in this list with the specified element.- Specified by:
setin 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())
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add
Appends the specified element to the end of this list.- Specified by:
addin interfaceCollection<E>- Specified by:
addin interfaceList<E>- Parameters:
e- element to be appended to this list- Returns:
true(as specified byCollection.add(E))
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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:
addin 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())
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addFirst
Adds an element as the first element of this collection (optional operation). After this operation completes normally, the given element will be a member of this collection, and it will be the first element in encounter order. -
addLast
Adds an element as the last element of this collection (optional operation). After this operation completes normally, the given element will be a member of this collection, and it will be the last element in encounter order. -
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:
removein 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())
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removeFirst
Removes and returns the first element of this collection (optional operation).- Specified by:
removeFirstin interfaceList<E>- Specified by:
removeFirstin interfaceSequencedCollection<E>- Returns:
- the removed element
- Throws:
NoSuchElementException- if this collection is empty- Since:
- 21
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removeLast
Removes and returns the last element of this collection (optional operation).- Specified by:
removeLastin interfaceList<E>- Specified by:
removeLastin interfaceSequencedCollection<E>- Returns:
- the removed element
- Throws:
NoSuchElementException- if this collection is empty- Since:
- 21
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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 indexisuch thatObjects.equals(o, get(i))(if such an element exists). Returnstrueif 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:
trueif the element was added
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containsAll
Returnstrueif this list contains all of the elements of the specified collection.- Specified by:
containsAllin interfaceCollection<E>- Specified by:
containsAllin interfaceList<E>- Parameters:
c- collection to be checked for containment in this list- Returns:
trueif this list contains all of the elements of the specified collection- Throws:
NullPointerException- if the specified collection is null- See Also:
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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:
removeAllin interfaceCollection<E>- Specified by:
removeAllin interfaceList<E>- Parameters:
c- collection containing elements to be removed from this list- Returns:
trueif 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:
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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:
retainAllin interfaceCollection<E>- Specified by:
retainAllin interfaceList<E>- Parameters:
c- collection containing elements to be retained in this list- Returns:
trueif 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:
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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:
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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:
addAllin interfaceCollection<E>- Specified by:
addAllin interfaceList<E>- Parameters:
c- collection containing elements to be added to this list- Returns:
trueif this list changed as a result of the call- Throws:
NullPointerException- if the specified collection is null- See Also:
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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:
addAllin 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:
trueif 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:
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forEach
Description copied from interface:IterablePerforms the given action for each element of theIterableuntil 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:
forEachin interfaceIterable<E>- Parameters:
action- The action to be performed for each element- Throws:
NullPointerException- if the specified action is null
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removeIf
Description copied from interface:CollectionRemoves 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:
removeIfin interfaceCollection<E>- Parameters:
filter- a predicate which returnstruefor elements to be removed- Returns:
trueif any elements were removed- Throws:
NullPointerException- if the specified filter is null
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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. Returnstrueif the specified object is the same object as this object, or if it is also aListand 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 elementse1ande2are 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
removemethod. -
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,setoraddmethods.- Specified by:
listIteratorin interfaceList<E>- Returns:
- a list iterator over the elements in this list (in proper sequence)
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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 topreviouswould 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,setoraddmethods.- Specified by:
listIteratorin 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())
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spliterator
Returns aSpliteratorover the elements in this list.The
SpliteratorreportsSpliterator.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:
spliteratorin interfaceCollection<E>- Specified by:
spliteratorin interfaceIterable<E>- Specified by:
spliteratorin interfaceList<E>- Returns:
- a
Spliteratorover the elements in this list - Since:
- 1.8
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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:
subListin 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)
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reversed
Returns a reverse-ordered view of this collection. The encounter order of elements in the returned view is the inverse of the encounter order of elements in this collection. The reverse ordering affects all order-sensitive operations, including those on the view collections of the returned view. If the collection implementation permits modifications to this view, the modifications "write through" to the underlying collection. Changes to the underlying collection might or might not be visible in this reversed view, depending upon the implementation.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.
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