E - the type of elements held in this collectionpublic 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.
public CopyOnWriteArrayList()
Creates an empty list.
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.
c - the collection of initially held elementsNullPointerException - if the specified collection is nullpublic CopyOnWriteArrayList(E[] toCopyIn)
Creates a list holding a copy of the given array.
toCopyIn - the array (a copy of this array is used as the internal array)NullPointerException - if the specified array is nullpublic int size()
Returns the number of elements in this list.
size in interface Collection<E>
size in interface List<E>
public boolean isEmpty()
Returns true if this list contains no elements.
isEmpty in interface Collection<E>
isEmpty in interface List<E>
true if this list contains no elementspublic 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)).
contains in interface Collection<E>
contains in interface List<E>
o - element whose presence in this list is to be testedtrue if this list contains the specified elementpublic 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.
indexOf in interface List<E>
o - element to search forpublic 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.
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)
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.
lastIndexOf in interface List<E>
o - element to search forpublic 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.
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()
Returns a shallow copy of this list. (The elements themselves are not copied.)
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.
toArray in interface Collection<E>
toArray in interface List<E>
Arrays.asList(Object[])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().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)
Returns the element at the specified position in this list.
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) Replaces the element at the specified position in this list with the specified 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)
Appends the specified element to the end of this list.
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) 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).
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)
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.
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)
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).
remove in interface Collection<E>
remove in interface List<E>
o - element to be removed from this list, if presenttrue if this list contained the specified elementpublic boolean addIfAbsent(E e)
Appends the element, if not present.
e - element to be added to this list, if absenttrue if the element was addedpublic boolean containsAll(Collection<?> c)
Returns 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)
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.
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)
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.
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)
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.
c - collection containing elements to be added to this listNullPointerException - if the specified collection is nulladdIfAbsent(Object)public void clear()
Removes all of the elements from this list. The list will be empty after this call returns.
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.
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) 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.
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)
Description copied from interface: Iterable
Performs the given action for each element of the 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.
forEach in interface Iterable<E>
action - The action to be performed for each elementpublic boolean removeIf(Predicate<? super E> filter)
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.
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)
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.
replaceAll in interface List<E>
operator - the operator to apply to each elementpublic void sort(Comparator<? super E> c)
Description copied from interface: List
Sorts this list according to the order induced by the specified 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()
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).
public boolean equals(Object o)
Compares the specified object with this list for equality. Returns 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()
Returns the hash code value for this list.
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()
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.
iterator in interface Iterable<E>
iterator in interface Collection<E>
iterator in interface List<E>
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.
listIterator in interface List<E>
public 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. 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.
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()
Returns a 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) 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.
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)
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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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