java.lang.Object
- java.util.concurrent.CopyOnWriteArrayList<E>

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 random-access list.
Read operations (including get(int)) do not block and may overlap with update operations. Reads reflect the results of the most recently completed operations. Aggregate operations like addAll(java.util.Collection<? extends E>) and clear() are atomic; they never expose an intermediate state.
Iterators of this list never throw ConcurrentModificationException. When an iterator is created, it keeps a copy of the list's contents. It is always safe to iterate this list, but iterations may not reflect the latest state of the list.
Iterators returned by this list and its sub lists cannot modify the underlying list. In particular, Iterator.remove(), ListIterator.add(E) and ListIterator.set(E) all throw UnsupportedOperationException.
This class offers extended API beyond the List interface. It includes additional overloads for indexed search (indexOf(E, int) and lastIndexOf(E, int)) and methods for conditional adds (addIfAbsent(E) and addAllAbsent(java.util.Collection<? extends E>)).

See Also:

Serialized Form

Constructor Summary

Constructors
Constructor	Description
`CopyOnWriteArrayList()`	Creates a new empty instance.
`CopyOnWriteArrayList(E[] array)`	Creates a new instance containing the elements of `array`.
`CopyOnWriteArrayList(Collection<? extends E> collection)`	Creates a new instance containing the elements of `collection`.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`void`	`add(int index, E e)`	Inserts the specified object into this `List` at the specified location.
`boolean`	`add(E e)`	Adds the specified object at the end of this `List`.
`boolean`	`addAll(int index, Collection<? extends E> collection)`	Inserts the objects in the specified collection at the specified location in this `List`.
`boolean`	`addAll(Collection<? extends E> collection)`	Adds the objects in the specified collection to the end of this `List`.
`int`	`addAllAbsent(Collection<? extends E> collection)`	Adds the elements of `collection` that are not already present in this list.
`boolean`	`addIfAbsent(E object)`	Adds `object` to the end of this list if it is not already present.
`void`	`clear()`	Removes all elements from this `List`, leaving it empty.
`Object`	`clone()`	Creates and returns a copy of this `Object`.
`boolean`	`contains(Object o)`	Tests whether this `List` contains the specified object.
`boolean`	`containsAll(Collection<?> collection)`	Tests whether this `List` contains all objects contained in the specified collection.
`boolean`	`equals(Object other)`	Compares this instance with the specified object and indicates if they are equal.
`E`	`get(int index)`	Returns the element at the specified location in this `List`.
`int`	`hashCode()`	Returns an integer hash code for this object.
`int`	`indexOf(E object, int from)`	Searches this list for `object` and returns the index of the first occurrence that is at or after `from`.
`int`	`indexOf(Object object)`	Searches this `List` for the specified object and returns the index of the first occurrence.
`boolean`	`isEmpty()`	Returns whether this `List` contains no elements.
`Iterator<E>`	`iterator()`	Returns an `Iterator` that iterates over the elements of this list as they were at the time of this method call.
`int`	`lastIndexOf(E object, int to)`	Searches this list for `object` and returns the index of the last occurrence that is before `to`.
`int`	`lastIndexOf(Object object)`	Searches this `List` for the specified object and returns the index of the last occurrence.
`ListIterator<E>`	`listIterator()`	Equivalent to `listIterator(0)`.
`ListIterator<E>`	`listIterator(int index)`	Returns a `ListIterator` that iterates over the elements of this list as they were at the time of this method call.
`E`	`remove(int index)`	Removes the object at the specified location from this `List`.
`boolean`	`remove(Object o)`	Removes the first occurrence of the specified object from this `List`.
`boolean`	`removeAll(Collection<?> collection)`	Removes all occurrences in this `List` of each object in the specified collection.
`boolean`	`retainAll(Collection<?> collection)`	Removes all objects from this `List` that are not contained in the specified collection.
`E`	`set(int index, E e)`	Replaces the element at the specified location in this `List` with the specified object.
`int`	`size()`	Returns the number of elements in this `List`.
`List<E>`	`subList(int from, int to)`	Returns a `List` of the specified portion of this `List` from the given start index to the end index minus one.
`Object[]`	`toArray()`	Returns an array containing all elements contained in this `List`.
`<T> T[]`	`toArray(T[] contents)`	Returns an array containing all elements contained in this `List`.
`String`	`toString()`	Returns a string containing a concise, human-readable description of this object.

Methods inherited from class java.lang.Object
finalize, getClass, notify, notifyAll, wait, wait, wait

- Constructor Detail
  - CopyOnWriteArrayList
```
public CopyOnWriteArrayList()
```
    Creates a new empty instance.
  - CopyOnWriteArrayList
```
public CopyOnWriteArrayList(Collection<? extends E> collection)
```
    Creates a new instance containing the elements of collection.
  - CopyOnWriteArrayList
```
public CopyOnWriteArrayList(E[] array)
```
    Creates a new instance containing the elements of array.
- Method Detail
  - clone
```
public Object clone()
```
    Description copied from class: Object
    
    Creates and returns a copy of this Object. The default implementation returns a so-called "shallow" copy: It creates a new instance of the same class and then copies the field values (including object references) from this instance to the new instance. A "deep" copy, in contrast, would also recursively clone nested objects. A subclass that needs to implement this kind of cloning should call super.clone() to create the new instance and then create deep copies of the nested, mutable objects.
    
    Overrides:
    
    clone in class Object
    
    Returns:
    
    a copy of this object.
  - size
```
public int size()
```
    Description copied from interface: List
    
    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.
  - get
```
public E get(int index)
```
    Description copied from interface: List
    
    Returns the element at the specified location in this List.
    
    Specified by:
    
    get in interface List<E>
    
    Parameters:
    
    index - the index of the element to return.
    
    Returns:
    
    the element at the specified location.
  - contains
```
public boolean contains(Object o)
```
    Description copied from interface: List
    
    Tests whether this List contains the specified object.
    
    Specified by:
    
    contains in interface Collection<E>
    
    Specified by:
    
    contains in interface List<E>
    
    Parameters:
    
    o - the object to search for.
    
    Returns:
    
    true if object is an element of this List, false otherwise
  - containsAll
```
public boolean containsAll(Collection<?> collection)
```
    Description copied from interface: List
    
    Tests whether this List contains all objects contained in the specified collection.
    
    Specified by:
    
    containsAll in interface Collection<E>
    
    Specified by:
    
    containsAll in interface List<E>
    
    Parameters:
    
    collection - the collection of objects
    
    Returns:
    
    true if all objects in the specified collection are elements of this List, false otherwise.
  - indexOf
```
public int indexOf(E object,
                   int from)
```
    Searches this list for object and returns the index of the first occurrence that is at or after from.
    
    Returns:
    
    the index or -1 if the object was not found.
  - indexOf
```
public int indexOf(Object object)
```
    Description copied from interface: List
    
    Searches this List for the specified object and returns the index of the first occurrence.
    
    Specified by:
    
    indexOf in interface List<E>
    
    Parameters:
    
    object - the object to search for.
    
    Returns:
    
    the index of the first occurrence of the object or -1 if the object was not found.
  - lastIndexOf
```
public int lastIndexOf(E object,
                       int to)
```
    Searches this list for object and returns the index of the last occurrence that is before to.
    
    Returns:
    
    the index or -1 if the object was not found.
  - lastIndexOf
```
public int lastIndexOf(Object object)
```
    Description copied from interface: List
    
    Searches this List for the specified object and returns the index of the last occurrence.
    
    Specified by:
    
    lastIndexOf in interface List<E>
    
    Parameters:
    
    object - the object to search for.
    
    Returns:
    
    the index of the last occurrence of the object, or -1 if the object was not found.
  - isEmpty
```
public boolean isEmpty()
```
    Description copied from interface: List
    
    Returns whether this List contains no elements.
    
    Specified by:
    
    isEmpty in interface Collection<E>
    
    Specified by:
    
    isEmpty in interface List<E>
    
    Returns:
    
    true if this List has no elements, false otherwise.
    
    See Also:
    
    List.size()
  - iterator
```
public Iterator<E> iterator()
```
    Returns an Iterator that iterates over the elements of this list as they were at the time of this method call. Changes to the list made after this method call will not be reflected by the iterator, nor will they trigger a ConcurrentModificationException.
    The returned iterator does not support Iterator.remove().
    
    Specified by:
    
    iterator in interface Collection<E>
    
    Specified by:
    
    iterator in interface Iterable<E>
    
    Specified by:
    
    iterator in interface List<E>
    
    Returns:
    
    an iterator on the elements of this List.
    
    See Also:
    
    Iterator
  - listIterator
```
public ListIterator<E> listIterator(int index)
```
    Returns a ListIterator that iterates over the elements of this list as they were at the time of this method call. Changes to the list made after this method call will not be reflected by the iterator, nor will they trigger a ConcurrentModificationException.
    The returned iterator does not support ListIterator.add(E), ListIterator.set(E) or Iterator.remove(),
    
    Specified by:
    
    listIterator in interface List<E>
    
    Parameters:
    
    index - the index at which to start the iteration.
    
    Returns:
    
    a list iterator on the elements of this List.
    
    See Also:
    
    ListIterator
  - listIterator
```
public ListIterator<E> listIterator()
```
    Equivalent to listIterator(0).
    
    Specified by:
    
    listIterator in interface List<E>
    
    Returns:
    
    a List iterator on the elements of this List
    
    See Also:
    
    ListIterator
  - subList
```
public List<E> subList(int from,
                       int to)
```
    Description copied from interface: List
    
    Returns a List of the specified portion of this List from the given start index to the end index minus one. The returned List is backed by this List so changes to it are reflected by the other.
    
    Specified by:
    
    subList in interface List<E>
    
    Parameters:
    
    from - the index at which to start the sublist.
    
    to - the index one past the end of the sublist.
    
    Returns:
    
    a list of a portion of this List.
  - toArray
```
public Object[] toArray()
```
    Description copied from interface: List
    
    Returns an array containing all elements contained in this List.
    
    Specified by:
    
    toArray in interface Collection<E>
    
    Specified by:
    
    toArray in interface List<E>
    
    Returns:
    
    an array of the elements from this List.
  - toArray
```
public <T> T[] toArray(T[] contents)
```
    Description copied from interface: List
    
    Returns an array containing all elements contained in this List. If the specified array is large enough to hold the elements, the specified array is used, otherwise an array of the same type is created. If the specified array is used and is larger than this List, the array element following the collection elements is set to null.
    
    Specified by:
    
    toArray in interface Collection<E>
    
    Specified by:
    
    toArray in interface List<E>
    
    Parameters:
    
    contents - the array.
    
    Returns:
    
    an array of the elements from this List.
  - equals
```
public boolean equals(Object other)
```
    Description copied from class: Object
    
    Compares this instance with the specified object and indicates if they are equal. In order to be equal, o must represent the same object as this instance using a class-specific comparison. The general contract is that this comparison should be reflexive, symmetric, and transitive. Also, no object reference other than null is equal to null.
    The default implementation returns true only if this == o. See Writing a correct equals method if you intend implementing your own equals method.
    The general contract for the equals and Object.hashCode() methods is that if equals returns true for any two objects, then hashCode() must return the same value for these objects. This means that subclasses of Object usually override either both methods or neither of them.
    
    Specified by:
    
    equals in interface Collection<E>
    
    Specified by:
    
    equals in interface List<E>
    
    Overrides:
    
    equals in class Object
    
    Parameters:
    
    other - the object to compare this instance with.
    
    Returns:
    
    true if the specified object is equal to this Object; false otherwise.
    
    See Also:
    
    Object.hashCode()
  - hashCode
```
public int hashCode()
```
    Description copied from class: Object
    
    Returns an integer hash code for this object. By contract, any two objects for which Object.equals(java.lang.Object) returns true must return the same hash code value. This means that subclasses of Object usually override both methods or neither method.
    Note that hash values must not change over time unless information used in equals comparisons also changes.
    See Writing a correct hashCode method if you intend implementing your own hashCode method.
    
    Specified by:
    
    hashCode in interface Collection<E>
    
    Specified by:
    
    hashCode in interface List<E>
    
    Overrides:
    
    hashCode in class Object
    
    Returns:
    
    this object's hash code.
    
    See Also:
    
    Object.equals(java.lang.Object)
  - toString
```
public String toString()
```
    Description copied from class: Object
    Returns a string containing a concise, human-readable description of this object. Subclasses are encouraged to override this method and provide an implementation that takes into account the object's type and data. The default implementation is equivalent to the following expression:
    getClass().getName() + '@' + Integer.toHexString(hashCode())
    
    See Writing a useful toString method if you intend implementing your own toString method.
    Overrides:
    
    toString in class Object
    
    Returns:
    
    a printable representation of this object.
  - add
```
public boolean add(E e)
```
    Description copied from interface: List
    
    Adds the specified object at the end of this List.
    
    Specified by:
    
    add in interface Collection<E>
    
    Specified by:
    
    add in interface List<E>
    
    Parameters:
    
    e - the object to add.
    
    Returns:
    
    always true.
  - add
```
public void add(int index,
                E e)
```
    Description copied from interface: List
    
    Inserts the specified object into this List at the specified location. The object is inserted before the current element at the specified location. If the location is equal to the size of this List, the object is added at the end. If the location is smaller than the size of this List, then all elements beyond the specified location are moved by one position towards the end of the List.
    
    Specified by:
    
    add in interface List<E>
    
    Parameters:
    
    index - the index at which to insert.
    
    e - the object to add.
  - addAll
```
public boolean addAll(Collection<? extends E> collection)
```
    Description copied from interface: List
    
    Adds the objects in the specified collection to the end of this List. The objects are added in the order in which they are returned from the collection's iterator.
    
    Specified by:
    
    addAll in interface Collection<E>
    
    Specified by:
    
    addAll in interface List<E>
    
    Parameters:
    
    collection - the collection of objects.
    
    Returns:
    
    true if this List is modified, false otherwise (i.e. if the passed collection was empty).
  - addAll
```
public boolean addAll(int index,
                      Collection<? extends E> collection)
```
    Description copied from interface: List
    
    Inserts the objects in the specified collection at the specified location in this List. The objects are added in the order they are returned from the collection's iterator.
    
    Specified by:
    
    addAll in interface List<E>
    
    Parameters:
    
    index - the index at which to insert.
    
    collection - the collection of objects to be inserted.
    
    Returns:
    
    true if this List has been modified through the insertion, false otherwise (i.e. if the passed collection was empty).
  - addAllAbsent
```
public int addAllAbsent(Collection<? extends E> collection)
```
    Adds the elements of collection that are not already present in this list. If collection includes a repeated value, at most one occurrence of that value will be added to this list. Elements are added at the end of this list.
    Callers of this method may prefer CopyOnWriteArraySet, whose API is more appropriate for set operations.
  - addIfAbsent
```
public boolean addIfAbsent(E object)
```
    Adds object to the end of this list if it is not already present.
    Callers of this method may prefer CopyOnWriteArraySet, whose API is more appropriate for set operations.
  - clear
```
public void clear()
```
    Description copied from interface: List
    
    Removes all elements from this List, leaving it empty.
    
    Specified by:
    
    clear in interface Collection<E>
    
    Specified by:
    
    clear in interface List<E>
    
    See Also:
    
    List.isEmpty(), List.size()
  - remove
```
public E remove(int index)
```
    Description copied from interface: List
    
    Removes the object at the specified location from this List.
    
    Specified by:
    
    remove in interface List<E>
    
    Parameters:
    
    index - the index of the object to remove.
    
    Returns:
    
    the removed object.
  - remove
```
public boolean remove(Object o)
```
    Description copied from interface: List
    
    Removes the first occurrence of the specified object from this List.
    
    Specified by:
    
    remove in interface Collection<E>
    
    Specified by:
    
    remove in interface List<E>
    
    Parameters:
    
    o - the object to remove.
    
    Returns:
    
    true if this List was modified by this operation, false otherwise.
  - removeAll
```
public boolean removeAll(Collection<?> collection)
```
    Description copied from interface: List
    
    Removes all occurrences in this List of each object in the specified collection.
    
    Specified by:
    
    removeAll in interface Collection<E>
    
    Specified by:
    
    removeAll in interface List<E>
    
    Parameters:
    
    collection - the collection of objects to remove.
    
    Returns:
    
    true if this List is modified, false otherwise.
  - retainAll
```
public boolean retainAll(Collection<?> collection)
```
    Description copied from interface: List
    
    Removes all objects from this List that are not contained in the specified collection.
    
    Specified by:
    
    retainAll in interface Collection<E>
    
    Specified by:
    
    retainAll in interface List<E>
    
    Parameters:
    
    collection - the collection of objects to retain.
    
    Returns:
    
    true if this List is modified, false otherwise.
  - set
```
public E set(int index,
             E e)
```
    Description copied from interface: List
    
    Replaces the element at the specified location in this List with the specified object. This operation does not change the size of the List.
    
    Specified by:
    
    set in interface List<E>
    
    Parameters:
    
    index - the index at which to put the specified object.
    
    e - the object to insert.
    
    Returns:
    
    the previous element at the index.

Class CopyOnWriteArrayList<E>

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

CopyOnWriteArrayList

CopyOnWriteArrayList

CopyOnWriteArrayList

Method Detail

clone

size

get

contains

containsAll

indexOf

indexOf

lastIndexOf

lastIndexOf

isEmpty

iterator

listIterator

listIterator

subList

toArray

toArray

equals

hashCode

toString

add

add

addAll

addAll

addAllAbsent

addIfAbsent

clear

remove

remove

removeAll

retainAll

set