# CopyOnWriteArrayList Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) Summary:[Ctors](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#pubctors)\|[Methods](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#pubmethods)\|[Inherited Methods](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#inhmethods) # CopyOnWriteArrayList ` public class CopyOnWriteArrayList ` ` extends `[Object](https://developer.android.com/reference/java/lang/Object)` `` implements `[Cloneable](https://developer.android.com/reference/java/lang/Cloneable)`, `[List](https://developer.android.com/reference/java/util/List)`, `[RandomAccess](https://developer.android.com/reference/java/util/RandomAccess)`, `[Serializable](https://developer.android.com/reference/java/io/Serializable)` ` |---|------------------------------------------------| | [java.lang.Object](https://developer.android.com/reference/java/lang/Object) || | ↳ | java.util.concurrent.CopyOnWriteArrayList\ |
*** ** * ** *** A thread-safe variant of[ArrayList](https://developer.android.com/reference/java/util/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*](https://developer.android.com/reference/java/util/concurrent/package-summary#MemoryVisibility)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](https://reference/java/util/package-summary.html#CollectionsFramework). ## Summary | ### Public constructors || |-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---| | ` `[CopyOnWriteArrayList](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#CopyOnWriteArrayList())`() ` Creates an empty list. | | ` `[CopyOnWriteArrayList](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#CopyOnWriteArrayList(E[]))`(E[] toCopyIn) ` Creates a list holding a copy of the given array. | | ` `[CopyOnWriteArrayList](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#CopyOnWriteArrayList(java.util.Collection))`(`[Collection](https://developer.android.com/reference/java/util/Collection)` c) ` Creates a list containing the elements of the specified collection, in the order they are returned by the collection's iterator. | | ### Public methods || |----------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | ` boolean` | ` `[add](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#add(E))`(E e) ` Appends the specified element to the end of this list. | | ` void` | ` `[add](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#add(int,%20E))`(int index, E element) ` Inserts the specified element at the specified position in this list. | | ` boolean` | ` `[addAll](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#addAll(java.util.Collection))`(`[Collection](https://developer.android.com/reference/java/util/Collection)` 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](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#addAll(int,%20java.util.Collection))`(int index, `[Collection](https://developer.android.com/reference/java/util/Collection)` c) ` Inserts all of the elements in the specified collection into this list, starting at the specified position. | | ` int` | ` `[addAllAbsent](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#addAllAbsent(java.util.Collection))`(`[Collection](https://developer.android.com/reference/java/util/Collection)` 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. | | ` void` | ` `[addFirst](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#addFirst(E))`(E e) ` Adds an element as the first element of this collection (optional operation). | | ` boolean` | ` `[addIfAbsent](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#addIfAbsent(E))`(E e) ` Appends the element, if not present. | | ` void` | ` `[addLast](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#addLast(E))`(E e) ` Adds an element as the last element of this collection (optional operation). | | ` void` | ` `[clear](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#clear())`() ` Removes all of the elements from this list. | | ` `[Object](https://developer.android.com/reference/java/lang/Object) | ` `[clone](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#clone())`() ` Returns a shallow copy of this list. | | ` boolean` | ` `[contains](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#contains(java.lang.Object))`(`[Object](https://developer.android.com/reference/java/lang/Object)` o) ` Returns`true`if this list contains the specified element. | | ` boolean` | ` `[containsAll](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#containsAll(java.util.Collection))`(`[Collection](https://developer.android.com/reference/java/util/Collection)` c) ` Returns`true`if this list contains all of the elements of the specified collection. | | ` boolean` | ` `[equals](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#equals(java.lang.Object))`(`[Object](https://developer.android.com/reference/java/lang/Object)` o) ` Compares the specified object with this list for equality. | | ` void` | ` `[forEach](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#forEach(java.util.function.Consumer))`(`[Consumer](https://developer.android.com/reference/java/util/function/Consumer)` action) ` | | ` E` | ` `[get](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#get(int))`(int index) ` Returns the element at the specified position in this list. | | ` E` | ` `[getFirst](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#getFirst())`() ` Gets the first element of this collection. | | ` E` | ` `[getLast](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#getLast())`() ` Gets the last element of this collection. | | ` int` | ` `[hashCode](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#hashCode())`() ` Returns the hash code value for this list. | | ` int` | ` `[indexOf](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#indexOf(E,%20int))`(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](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#indexOf(java.lang.Object))`(`[Object](https://developer.android.com/reference/java/lang/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](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#isEmpty())`() ` Returns`true`if this list contains no elements. | | ` `[Iterator](https://developer.android.com/reference/java/util/Iterator)`` | ` `[iterator](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#iterator())`() ` Returns an iterator over the elements in this list in proper sequence. | | ` int` | ` `[lastIndexOf](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#lastIndexOf(java.lang.Object))`(`[Object](https://developer.android.com/reference/java/lang/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. | | ` int` | ` `[lastIndexOf](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#lastIndexOf(E,%20int))`(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. | | ` `[ListIterator](https://developer.android.com/reference/java/util/ListIterator)`` | ` `[listIterator](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#listIterator(int))`(int index) ` Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list. The returned iterator provides a snapshot of the state of the list when the iterator was constructed. | | ` `[ListIterator](https://developer.android.com/reference/java/util/ListIterator)`` | ` `[listIterator](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#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. | | ` E` | ` `[remove](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#remove(int))`(int index) ` Removes the element at the specified position in this list. | | ` boolean` | ` `[remove](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#remove(java.lang.Object))`(`[Object](https://developer.android.com/reference/java/lang/Object)` o) ` Removes the first occurrence of the specified element from this list, if it is present. | | ` boolean` | ` `[removeAll](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#removeAll(java.util.Collection))`(`[Collection](https://developer.android.com/reference/java/util/Collection)` c) ` Removes from this list all of its elements that are contained in the specified collection. | | ` E` | ` `[removeFirst](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#removeFirst())`() ` Removes and returns the first element of this collection (optional operation). | | ` boolean` | ` `[removeIf](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#removeIf(java.util.function.Predicate))`(`[Predicate](https://developer.android.com/reference/java/util/function/Predicate)` filter) ` Removes all of the elements of this collection that satisfy the given predicate. | | ` E` | ` `[removeLast](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#removeLast())`() ` Removes and returns the last element of this collection (optional operation). | | ` void` | ` `[replaceAll](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#replaceAll(java.util.function.UnaryOperator))`(`[UnaryOperator](https://developer.android.com/reference/java/util/function/UnaryOperator)` operator) ` Replaces each element of this list with the result of applying the operator to that element. | | ` boolean` | ` `[retainAll](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#retainAll(java.util.Collection))`(`[Collection](https://developer.android.com/reference/java/util/Collection)` c) ` Retains only the elements in this list that are contained in the specified collection. | | ` `[List](https://developer.android.com/reference/java/util/List)`` | ` `[reversed](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#reversed())`() ` Returns a reverse-ordered[view](https://developer.android.com/reference/java/util/concurrent/Collection#view)of this collection. Modifications to the reversed view are permitted and will be propagated to this list. | | ` E` | ` `[set](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#set(int,%20E))`(int index, E element) ` Replaces the element at the specified position in this list with the specified element. | | ` int` | ` `[size](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#size())`() ` Returns the number of elements in this list. | | ` void` | ` `[sort](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#sort(java.util.Comparator))`(`[Comparator](https://developer.android.com/reference/java/util/Comparator)` c) ` Sorts this list according to the order induced by the specified[Comparator](https://developer.android.com/reference/java/util/Comparator). | | ` `[Spliterator](https://developer.android.com/reference/java/util/Spliterator)`` | ` `[spliterator](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#spliterator())`() ` Returns a[Spliterator](https://developer.android.com/reference/java/util/Spliterator)over the elements in this list. | | ` `[List](https://developer.android.com/reference/java/util/List)`` | ` `[subList](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#subList(int,%20int))`(int fromIndex, int toIndex) ` Returns a view of the portion of this list between`fromIndex`, inclusive, and`toIndex`, exclusive. | | ` `[Object[]](https://developer.android.com/reference/java/lang/Object) | ` `[toArray](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#toArray())`() ` Returns an array containing all of the elements in this list in proper sequence (from first to last element). | | ` T[]` | ` `[toArray](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#toArray(T[]))`(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](https://developer.android.com/reference/java/lang/String) | ` `[toString](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#toString())`() ` Returns a string representation of this list. | | ### Inherited methods | |-----------------------|---| | From class` `[java.lang.Object](https://developer.android.com/reference/java/lang/Object)` ` |--------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | ` `[Object](https://developer.android.com/reference/java/lang/Object) | ` `[clone](https://developer.android.com/reference/java/lang/Object#clone())`() ` Creates and returns a copy of this object. | | ` boolean` | ` `[equals](https://developer.android.com/reference/java/lang/Object#equals(java.lang.Object))`(`[Object](https://developer.android.com/reference/java/lang/Object)` obj) ` Indicates whether some other object is "equal to" this one. | | ` void` | ` `[finalize](https://developer.android.com/reference/java/lang/Object#finalize())`() ` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. | | ` final `[Class](https://developer.android.com/reference/java/lang/Class)`` | ` `[getClass](https://developer.android.com/reference/java/lang/Object#getClass())`() ` Returns the runtime class of this`Object`. | | ` int` | ` `[hashCode](https://developer.android.com/reference/java/lang/Object#hashCode())`() ` Returns a hash code value for the object. | | ` final void` | ` `[notify](https://developer.android.com/reference/java/lang/Object#notify())`() ` Wakes up a single thread that is waiting on this object's monitor. | | ` final void` | ` `[notifyAll](https://developer.android.com/reference/java/lang/Object#notifyAll())`() ` Wakes up all threads that are waiting on this object's monitor. | | ` `[String](https://developer.android.com/reference/java/lang/String) | ` `[toString](https://developer.android.com/reference/java/lang/Object#toString())`() ` Returns a string representation of the object. | | ` final void` | ` `[wait](https://developer.android.com/reference/java/lang/Object#wait(long,%20int))`(long timeoutMillis, int nanos) ` Causes the current thread to wait until it is awakened, typically by being*notified* or*interrupted*, or until a certain amount of real time has elapsed. | | ` final void` | ` `[wait](https://developer.android.com/reference/java/lang/Object#wait(long))`(long timeoutMillis) ` Causes the current thread to wait until it is awakened, typically by being*notified* or*interrupted*, or until a certain amount of real time has elapsed. | | ` final void` | ` `[wait](https://developer.android.com/reference/java/lang/Object#wait())`() ` Causes the current thread to wait until it is awakened, typically by being*notified* or*interrupted*. | || | From interface` `[java.util.List](https://developer.android.com/reference/java/util/List)` ` |-------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | ` abstract boolean` | ` `[add](https://developer.android.com/reference/java/util/List#add(E))`(E e) ` Appends the specified element to the end of this list (optional operation). | | ` abstract void` | ` `[add](https://developer.android.com/reference/java/util/List#add(int,%20E))`(int index, E element) ` Inserts the specified element at the specified position in this list (optional operation). | | ` abstract boolean` | ` `[addAll](https://developer.android.com/reference/java/util/List#addAll(java.util.Collection))`(`[Collection](https://developer.android.com/reference/java/util/Collection)` 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 (optional operation). | | ` abstract boolean` | ` `[addAll](https://developer.android.com/reference/java/util/List#addAll(int,%20java.util.Collection))`(int index, `[Collection](https://developer.android.com/reference/java/util/Collection)` c) ` Inserts all of the elements in the specified collection into this list at the specified position (optional operation). | | ` default void` | ` `[addFirst](https://developer.android.com/reference/java/util/List#addFirst(E))`(E e) ` Adds an element as the first element of this collection (optional operation). | | ` default void` | ` `[addLast](https://developer.android.com/reference/java/util/List#addLast(E))`(E e) ` Adds an element as the last element of this collection (optional operation). | | ` abstract void` | ` `[clear](https://developer.android.com/reference/java/util/List#clear())`() ` Removes all of the elements from this list (optional operation). | | ` abstract boolean` | ` `[contains](https://developer.android.com/reference/java/util/List#contains(java.lang.Object))`(`[Object](https://developer.android.com/reference/java/lang/Object)` o) ` Returns`true`if this list contains the specified element. | | ` abstract boolean` | ` `[containsAll](https://developer.android.com/reference/java/util/List#containsAll(java.util.Collection))`(`[Collection](https://developer.android.com/reference/java/util/Collection)` c) ` Returns`true`if this list contains all of the elements of the specified collection. | | ` static `[List](https://developer.android.com/reference/java/util/List)`` | ` `[copyOf](https://developer.android.com/reference/java/util/List#copyOf(java.util.Collection))`(`[Collection](https://developer.android.com/reference/java/util/Collection)` coll) ` Returns an[unmodifiable List](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#unmodifiable)containing the elements of the given Collection, in its iteration order. | | ` abstract boolean` | ` `[equals](https://developer.android.com/reference/java/util/List#equals(java.lang.Object))`(`[Object](https://developer.android.com/reference/java/lang/Object)` o) ` Compares the specified object with this list for equality. | | ` abstract E` | ` `[get](https://developer.android.com/reference/java/util/List#get(int))`(int index) ` Returns the element at the specified position in this list. | | ` default E` | ` `[getFirst](https://developer.android.com/reference/java/util/List#getFirst())`() ` Gets the first element of this collection. | | ` default E` | ` `[getLast](https://developer.android.com/reference/java/util/List#getLast())`() ` Gets the last element of this collection. | | ` abstract int` | ` `[hashCode](https://developer.android.com/reference/java/util/List#hashCode())`() ` Returns the hash code value for this list. | | ` abstract int` | ` `[indexOf](https://developer.android.com/reference/java/util/List#indexOf(java.lang.Object))`(`[Object](https://developer.android.com/reference/java/lang/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. | | ` abstract boolean` | ` `[isEmpty](https://developer.android.com/reference/java/util/List#isEmpty())`() ` Returns`true`if this list contains no elements. | | ` abstract `[Iterator](https://developer.android.com/reference/java/util/Iterator)`` | ` `[iterator](https://developer.android.com/reference/java/util/List#iterator())`() ` Returns an iterator over the elements in this list in proper sequence. | | ` abstract int` | ` `[lastIndexOf](https://developer.android.com/reference/java/util/List#lastIndexOf(java.lang.Object))`(`[Object](https://developer.android.com/reference/java/lang/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. | | ` abstract `[ListIterator](https://developer.android.com/reference/java/util/ListIterator)`` | ` `[listIterator](https://developer.android.com/reference/java/util/List#listIterator(int))`(int index) ` Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list. | | ` abstract `[ListIterator](https://developer.android.com/reference/java/util/ListIterator)`` | ` `[listIterator](https://developer.android.com/reference/java/util/List#listIterator())`() ` Returns a list iterator over the elements in this list (in proper sequence). | | ` static `[List](https://developer.android.com/reference/java/util/List)`` | ` `[of](https://developer.android.com/reference/java/util/List#of(E,%20E,%20E))`(E e1, E e2, E e3) ` Returns an unmodifiable list containing three elements. | | ` static `[List](https://developer.android.com/reference/java/util/List)`` | ` `[of](https://developer.android.com/reference/java/util/List#of(E,%20E,%20E,%20E,%20E,%20E,%20E,%20E,%20E))`(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9) ` Returns an unmodifiable list containing nine elements. | | ` static `[List](https://developer.android.com/reference/java/util/List)`` | ` `[of](https://developer.android.com/reference/java/util/List#of(E,%20E,%20E,%20E,%20E))`(E e1, E e2, E e3, E e4, E e5) ` Returns an unmodifiable list containing five elements. | | ` static `[List](https://developer.android.com/reference/java/util/List)`` | ` `[of](https://developer.android.com/reference/java/util/List#of(E,%20E,%20E,%20E,%20E,%20E))`(E e1, E e2, E e3, E e4, E e5, E e6) ` Returns an unmodifiable list containing six elements. | | ` static `[List](https://developer.android.com/reference/java/util/List)`` | ` `[of](https://developer.android.com/reference/java/util/List#of(E,%20E,%20E,%20E,%20E,%20E,%20E,%20E))`(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8) ` Returns an unmodifiable list containing eight elements. | | ` static `[List](https://developer.android.com/reference/java/util/List)`` | ` `[of](https://developer.android.com/reference/java/util/List#of(E[]))`(E... elements) ` Returns an unmodifiable list containing an arbitrary number of elements. | | ` static `[List](https://developer.android.com/reference/java/util/List)`` | ` `[of](https://developer.android.com/reference/java/util/List#of())`() ` Returns an unmodifiable list containing zero elements. | | ` static `[List](https://developer.android.com/reference/java/util/List)`` | ` `[of](https://developer.android.com/reference/java/util/List#of(E,%20E,%20E,%20E,%20E,%20E,%20E,%20E,%20E,%20E))`(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10) ` Returns an unmodifiable list containing ten elements. | | ` static `[List](https://developer.android.com/reference/java/util/List)`` | ` `[of](https://developer.android.com/reference/java/util/List#of(E,%20E))`(E e1, E e2) ` Returns an unmodifiable list containing two elements. | | ` static `[List](https://developer.android.com/reference/java/util/List)`` | ` `[of](https://developer.android.com/reference/java/util/List#of(E,%20E,%20E,%20E,%20E,%20E,%20E))`(E e1, E e2, E e3, E e4, E e5, E e6, E e7) ` Returns an unmodifiable list containing seven elements. | | ` static `[List](https://developer.android.com/reference/java/util/List)`` | ` `[of](https://developer.android.com/reference/java/util/List#of(E,%20E,%20E,%20E))`(E e1, E e2, E e3, E e4) ` Returns an unmodifiable list containing four elements. | | ` static `[List](https://developer.android.com/reference/java/util/List)`` | ` `[of](https://developer.android.com/reference/java/util/List#of(E))`(E e1) ` Returns an unmodifiable list containing one element. | | ` abstract E` | ` `[remove](https://developer.android.com/reference/java/util/List#remove(int))`(int index) ` Removes the element at the specified position in this list (optional operation). | | ` abstract boolean` | ` `[remove](https://developer.android.com/reference/java/util/List#remove(java.lang.Object))`(`[Object](https://developer.android.com/reference/java/lang/Object)` o) ` Removes the first occurrence of the specified element from this list, if it is present (optional operation). | | ` abstract boolean` | ` `[removeAll](https://developer.android.com/reference/java/util/List#removeAll(java.util.Collection))`(`[Collection](https://developer.android.com/reference/java/util/Collection)` c) ` Removes from this list all of its elements that are contained in the specified collection (optional operation). | | ` default E` | ` `[removeFirst](https://developer.android.com/reference/java/util/List#removeFirst())`() ` Removes and returns the first element of this collection (optional operation). | | ` default E` | ` `[removeLast](https://developer.android.com/reference/java/util/List#removeLast())`() ` Removes and returns the last element of this collection (optional operation). | | ` default void` | ` `[replaceAll](https://developer.android.com/reference/java/util/List#replaceAll(java.util.function.UnaryOperator))`(`[UnaryOperator](https://developer.android.com/reference/java/util/function/UnaryOperator)` operator) ` Replaces each element of this list with the result of applying the operator to that element. | | ` abstract boolean` | ` `[retainAll](https://developer.android.com/reference/java/util/List#retainAll(java.util.Collection))`(`[Collection](https://developer.android.com/reference/java/util/Collection)` c) ` Retains only the elements in this list that are contained in the specified collection (optional operation). | | ` default `[List](https://developer.android.com/reference/java/util/List)`` | ` `[reversed](https://developer.android.com/reference/java/util/List#reversed())`() ` Returns a reverse-ordered[view](https://developer.android.com/reference/java/util/concurrent/Collection#view)of this collection. | | ` abstract E` | ` `[set](https://developer.android.com/reference/java/util/List#set(int,%20E))`(int index, E element) ` Replaces the element at the specified position in this list with the specified element (optional operation). | | ` abstract int` | ` `[size](https://developer.android.com/reference/java/util/List#size())`() ` Returns the number of elements in this list. | | ` default void` | ` `[sort](https://developer.android.com/reference/java/util/List#sort(java.util.Comparator))`(`[Comparator](https://developer.android.com/reference/java/util/Comparator)` c) ` Sorts this list according to the order induced by the specified[Comparator](https://developer.android.com/reference/java/util/Comparator). | | ` default `[Spliterator](https://developer.android.com/reference/java/util/Spliterator)`` | ` `[spliterator](https://developer.android.com/reference/java/util/List#spliterator())`() ` Creates a[Spliterator](https://developer.android.com/reference/java/util/Spliterator)over the elements in this list. | | ` abstract `[List](https://developer.android.com/reference/java/util/List)`` | ` `[subList](https://developer.android.com/reference/java/util/List#subList(int,%20int))`(int fromIndex, int toIndex) ` Returns a view of the portion of this list between the specified`fromIndex`, inclusive, and`toIndex`, exclusive. | | ` abstract `[Object[]](https://developer.android.com/reference/java/lang/Object) | ` `[toArray](https://developer.android.com/reference/java/util/List#toArray())`() ` Returns an array containing all of the elements in this list in proper sequence (from first to last element). | | ` abstract T[]` | ` `[toArray](https://developer.android.com/reference/java/util/List#toArray(T[]))`(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. | || | From interface` `[java.util.Collection](https://developer.android.com/reference/java/util/Collection)` ` |----------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | ` abstract boolean` | ` `[add](https://developer.android.com/reference/java/util/Collection#add(E))`(E e) ` Ensures that this collection contains the specified element (optional operation). | | ` abstract boolean` | ` `[addAll](https://developer.android.com/reference/java/util/Collection#addAll(java.util.Collection))`(`[Collection](https://developer.android.com/reference/java/util/Collection)` c) ` Adds all of the elements in the specified collection to this collection (optional operation). | | ` abstract void` | ` `[clear](https://developer.android.com/reference/java/util/Collection#clear())`() ` Removes all of the elements from this collection (optional operation). | | ` abstract boolean` | ` `[contains](https://developer.android.com/reference/java/util/Collection#contains(java.lang.Object))`(`[Object](https://developer.android.com/reference/java/lang/Object)` o) ` Returns`true`if this collection contains the specified element. | | ` abstract boolean` | ` `[containsAll](https://developer.android.com/reference/java/util/Collection#containsAll(java.util.Collection))`(`[Collection](https://developer.android.com/reference/java/util/Collection)` c) ` Returns`true`if this collection contains all of the elements in the specified collection. | | ` abstract boolean` | ` `[equals](https://developer.android.com/reference/java/util/Collection#equals(java.lang.Object))`(`[Object](https://developer.android.com/reference/java/lang/Object)` o) ` Compares the specified object with this collection for equality. | | ` abstract int` | ` `[hashCode](https://developer.android.com/reference/java/util/Collection#hashCode())`() ` Returns the hash code value for this collection. | | ` abstract boolean` | ` `[isEmpty](https://developer.android.com/reference/java/util/Collection#isEmpty())`() ` Returns`true`if this collection contains no elements. | | ` abstract `[Iterator](https://developer.android.com/reference/java/util/Iterator)`` | ` `[iterator](https://developer.android.com/reference/java/util/Collection#iterator())`() ` Returns an iterator over the elements in this collection. | | ` default `[Stream](https://developer.android.com/reference/java/util/stream/Stream)`` | ` `[parallelStream](https://developer.android.com/reference/java/util/Collection#parallelStream())`() ` Returns a possibly parallel`Stream`with this collection as its source. | | ` abstract boolean` | ` `[remove](https://developer.android.com/reference/java/util/Collection#remove(java.lang.Object))`(`[Object](https://developer.android.com/reference/java/lang/Object)` o) ` Removes a single instance of the specified element from this collection, if it is present (optional operation). | | ` abstract boolean` | ` `[removeAll](https://developer.android.com/reference/java/util/Collection#removeAll(java.util.Collection))`(`[Collection](https://developer.android.com/reference/java/util/Collection)` c) ` Removes all of this collection's elements that are also contained in the specified collection (optional operation). | | ` default boolean` | ` `[removeIf](https://developer.android.com/reference/java/util/Collection#removeIf(java.util.function.Predicate))`(`[Predicate](https://developer.android.com/reference/java/util/function/Predicate)` filter) ` Removes all of the elements of this collection that satisfy the given predicate. | | ` abstract boolean` | ` `[retainAll](https://developer.android.com/reference/java/util/Collection#retainAll(java.util.Collection))`(`[Collection](https://developer.android.com/reference/java/util/Collection)` c) ` Retains only the elements in this collection that are contained in the specified collection (optional operation). | | ` abstract int` | ` `[size](https://developer.android.com/reference/java/util/Collection#size())`() ` Returns the number of elements in this collection. | | ` default `[Spliterator](https://developer.android.com/reference/java/util/Spliterator)`` | ` `[spliterator](https://developer.android.com/reference/java/util/Collection#spliterator())`() ` Creates a[Spliterator](https://developer.android.com/reference/java/util/Spliterator)over the elements in this collection. | | ` default `[Stream](https://developer.android.com/reference/java/util/stream/Stream)`` | ` `[stream](https://developer.android.com/reference/java/util/Collection#stream())`() ` Returns a sequential`Stream`with this collection as its source. | | ` abstract T[]` | ` `[toArray](https://developer.android.com/reference/java/util/Collection#toArray(T[]))`(T[] a) ` Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array. | | ` abstract `[Object[]](https://developer.android.com/reference/java/lang/Object) | ` `[toArray](https://developer.android.com/reference/java/util/Collection#toArray())`() ` Returns an array containing all of the elements in this collection. | | ` default T[]` | ` `[toArray](https://developer.android.com/reference/java/util/Collection#toArray(java.util.function.IntFunction))`(`[IntFunction](https://developer.android.com/reference/java/util/function/IntFunction)` generator) ` Returns an array containing all of the elements in this collection, using the provided`generator`function to allocate the returned array. | || | From interface` `[java.util.SequencedCollection](https://developer.android.com/reference/java/util/SequencedCollection)` ` |---------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | ` default void` | ` `[addFirst](https://developer.android.com/reference/java/util/SequencedCollection#addFirst(E))`(E e) ` Adds an element as the first element of this collection (optional operation). | | ` default void` | ` `[addLast](https://developer.android.com/reference/java/util/SequencedCollection#addLast(E))`(E e) ` Adds an element as the last element of this collection (optional operation). | | ` default E` | ` `[getFirst](https://developer.android.com/reference/java/util/SequencedCollection#getFirst())`() ` Gets the first element of this collection. | | ` default E` | ` `[getLast](https://developer.android.com/reference/java/util/SequencedCollection#getLast())`() ` Gets the last element of this collection. | | ` default E` | ` `[removeFirst](https://developer.android.com/reference/java/util/SequencedCollection#removeFirst())`() ` Removes and returns the first element of this collection (optional operation). | | ` default E` | ` `[removeLast](https://developer.android.com/reference/java/util/SequencedCollection#removeLast())`() ` Removes and returns the last element of this collection (optional operation). | | ` abstract `[SequencedCollection](https://developer.android.com/reference/java/util/SequencedCollection)`` | ` `[reversed](https://developer.android.com/reference/java/util/SequencedCollection#reversed())`() ` Returns a reverse-ordered[view](https://developer.android.com/reference/java/util/concurrent/Collection#view)of this collection. | || | From interface` `[java.lang.Iterable](https://developer.android.com/reference/java/lang/Iterable)` ` |----------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | ` default void` | ` `[forEach](https://developer.android.com/reference/java/lang/Iterable#forEach(java.util.function.Consumer))`(`[Consumer](https://developer.android.com/reference/java/util/function/Consumer)` action) ` Performs the given action for each element of the`Iterable`until all elements have been processed or the action throws an exception. | | ` abstract `[Iterator](https://developer.android.com/reference/java/util/Iterator)`` | ` `[iterator](https://developer.android.com/reference/java/lang/Iterable#iterator())`() ` Returns an iterator over elements of type`T`. | | ` default `[Spliterator](https://developer.android.com/reference/java/util/Spliterator)`` | ` `[spliterator](https://developer.android.com/reference/java/lang/Iterable#spliterator())`() ` Creates a[Spliterator](https://developer.android.com/reference/java/util/Spliterator)over the elements described by this`Iterable`. | || ## Public constructors ### CopyOnWriteArrayList Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public CopyOnWriteArrayList () ``` Creates an empty list.
### CopyOnWriteArrayList Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public CopyOnWriteArrayList (E[] toCopyIn) ``` Creates a list holding a copy of the given array.
| Parameters || |------------|----------------------------------------------------------------------------| | `toCopyIn` | `E`: the array (a copy of this array is used as the internal array)
| | Throws || |------------------------------------------------------------------------------------------------|--------------------------------| | [NullPointerException](https://developer.android.com/reference/java/lang/NullPointerException) | if the specified array is null | ### CopyOnWriteArrayList Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public CopyOnWriteArrayList (Collection c) ``` Creates a list containing the elements of the specified collection, in the order they are returned by the collection's iterator.
| Parameters || |-----|----------------------------------------------------------------| | `c` | `Collection`: the collection of initially held elements
| | Throws || |------------------------------------------------------------------------------------------------|-------------------------------------| | [NullPointerException](https://developer.android.com/reference/java/lang/NullPointerException) | if the specified collection is null | ## Public methods ### add Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public boolean add (E e) ``` Appends the specified element to the end of this list.
| Parameters || |-----|-------------------------------------------------| | `e` | `E`: element to be appended to this list
| | Returns || |-----------|---------------------------------------------------------------------------------------------------------------------| | `boolean` | `true`(as specified by[Collection.add](https://developer.android.com/reference/java/util/Collection#add(E)))
| ### add Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` 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).
| Parameters || |-----------|----------------------------------------------------------------------| | `index` | `int`: index at which the specified element is to be inserted
| | `element` | `E`: element to be inserted
| | Throws || |----------------------------------------------------------------------------------------------------------|---| | [IndexOutOfBoundsException](https://developer.android.com/reference/java/lang/IndexOutOfBoundsException) | | ### addAll Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public boolean addAll (Collection 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.
| Parameters || |-----|------------------------------------------------------------------------------| | `c` | `Collection`: collection containing elements to be added to this list
| | Returns || |-----------|-----------------------------------------------------------| | `boolean` | `true`if this list changed as a result of the call
| | Throws || |------------------------------------------------------------------------------------------------|-------------------------------------| | [NullPointerException](https://developer.android.com/reference/java/lang/NullPointerException) | if the specified collection is null | **See also:** - [add(Object)](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#add(E)) ### addAll Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public boolean addAll (int index, Collection 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.
| Parameters || |---------|----------------------------------------------------------------------------------------| | `index` | `int`: index at which to insert the first element from the specified collection
| | `c` | `Collection`: collection containing elements to be added to this list
| | Returns || |-----------|-----------------------------------------------------------| | `boolean` | `true`if this list changed as a result of the call
| | Throws || |----------------------------------------------------------------------------------------------------------|-------------------------------------| | [IndexOutOfBoundsException](https://developer.android.com/reference/java/lang/IndexOutOfBoundsException) | | | [NullPointerException](https://developer.android.com/reference/java/lang/NullPointerException) | if the specified collection is null | **See also:** - [add(int, Object)](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#add(int,%20E)) ### addAllAbsent Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public int addAllAbsent (Collection 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`: collection containing elements to be added to this list
| | Returns || |-------|-------------------------------------| | `int` | the number of elements added
| | Throws || |------------------------------------------------------------------------------------------------|-------------------------------------| | [NullPointerException](https://developer.android.com/reference/java/lang/NullPointerException) | if the specified collection is null | **See also:** - [addIfAbsent(Object)](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#addIfAbsent(E)) ### addFirst Added in[API level 35](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public void addFirst (E e) ``` 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.
| Parameters || |-----|-------------------------------------| | `e` | `E`: the element to be added
| ### addIfAbsent Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public boolean addIfAbsent (E e) ``` Appends the element, if not present.
| Parameters || |-----|---------------------------------------------------------| | `e` | `E`: element to be added to this list, if absent
| | Returns || |-----------|---------------------------------------| | `boolean` | `true`if the element was added
| ### addLast Added in[API level 35](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public void addLast (E e) ``` 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.
| Parameters || |-----|--------------------------------------| | `e` | `E`: the element to be added.
| ### clear Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public void clear () ``` Removes all of the elements from this list. The list will be empty after this call returns.
### clone Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public Object clone () ``` Returns a shallow copy of this list. (The elements themselves are not copied.)
| Returns || |--------------------------------------------------------------------|-----------------------------| | [Object](https://developer.android.com/reference/java/lang/Object) | a clone of this list
| ### contains Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` 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`Objects.equals(o, e)`.
| Parameters || |-----|----------------------------------------------------------------------| | `o` | `Object`: element whose presence in this list is to be tested
| | Returns || |-----------|----------------------------------------------------------| | `boolean` | `true`if this list contains the specified element
| ### containsAll Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public boolean containsAll (Collection c) ``` Returns`true`if this list contains all of the elements of the specified collection.
| Parameters || |-----|----------------------------------------------------------------------------| | `c` | `Collection`: collection to be checked for containment in this list
| | Returns || |-----------|------------------------------------------------------------------------------------| | `boolean` | `true`if this list contains all of the elements of the specified collection
| | Throws || |------------------------------------------------------------------------------------------------|-------------------------------------| | [NullPointerException](https://developer.android.com/reference/java/lang/NullPointerException) | if the specified collection is null | **See also:** - [contains(Object)](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#contains(java.lang.Object)) ### equals Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` 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](https://developer.android.com/reference/java/util/List)and the sequence of elements returned by an[iterator](https://developer.android.com/reference/java/util/List#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`Objects.equals(e1, e2)`.
| Parameters || |-----|------------------------------------------------------------------------| | `o` | `Object`: the object to be compared for equality with this list
| | Returns || |-----------|------------------------------------------------------------| | `boolean` | `true`if the specified object is equal to this list
| ### forEach Added in[API level 24](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public void forEach (Consumer action) ```

| Parameters || |----------|-------------------| | `action` | `Consumer`
| | Throws || |------------------------------------------------------------------------------------------------|---| | [NullPointerException](https://developer.android.com/reference/java/lang/NullPointerException) | | ### get Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public E get (int index) ``` Returns the element at the specified position in this list.
| Parameters || |---------|----------------------------------------------| | `index` | `int`: index of the element to return
| | Returns || |-----|-----------------------------------------------------------| | `E` | the element at the specified position in this list
| | Throws || |----------------------------------------------------------------------------------------------------------|---| | [IndexOutOfBoundsException](https://developer.android.com/reference/java/lang/IndexOutOfBoundsException) | | ### getFirst Added in[API level 35](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public E getFirst () ``` Gets the first element of this collection.
| Returns || |-----|------------------------------| | `E` | the retrieved element
| | Throws || |----------------------------------------------------------------------------------------------------|---| | [NoSuchElementException](https://developer.android.com/reference/java/util/NoSuchElementException) | | ### getLast Added in[API level 35](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public E getLast () ``` Gets the last element of this collection.
| Returns || |-----|------------------------------| | `E` | the retrieved element
| | Throws || |----------------------------------------------------------------------------------------------------|---| | [NoSuchElementException](https://developer.android.com/reference/java/util/NoSuchElementException) | | ### hashCode Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public int hashCode () ``` Returns the hash code value for this list. This implementation uses the definition in[List.hashCode](https://developer.android.com/reference/java/util/List#hashCode()).
| Returns || |-------|------------------------------------------| | `int` | the hash code value for this list
| ### indexOf Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` 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 && Objects.equals(get(i), e)`, or -1 if there is no such index.
| Parameters || |---------|---------------------------------------------| | `e` | `E`: element to search for
| | `index` | `int`: index to start searching from
| | Returns || |-------|----------------------------------------------------------------------------------------------------------------------------------------------| | `int` | 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](https://developer.android.com/reference/java/lang/IndexOutOfBoundsException) | if the specified index is negative | ### indexOf Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` 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`Objects.equals(o, get(i))`, or -1 if there is no such index.
| Parameters || |-----|----------------------------------------| | `o` | `Object`: element to search for
| | Returns || |-------|---------------------------------------------------------------------------------------------------------------------------------| | `int` | the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element
| ### isEmpty Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public boolean isEmpty () ``` Returns`true`if this list contains no elements.
| Returns || |-----------|------------------------------------------------| | `boolean` | `true`if this list contains no elements
| ### iterator Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public Iterator 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.
| Returns || |-----------------------------------------------------------------------------|----------------------------------------------------------------------| | [Iterator](https://developer.android.com/reference/java/util/Iterator)`` | an iterator over the elements in this list in proper sequence
| ### lastIndexOf Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` 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`Objects.equals(o, get(i))`, or -1 if there is no such index.
| Parameters || |-----|----------------------------------------| | `o` | `Object`: element to search for
| | Returns || |-------|--------------------------------------------------------------------------------------------------------------------------------| | `int` | the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element
| ### lastIndexOf Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` 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 && Objects.equals(get(i), e)`, or -1 if there is no such index.
| Parameters || |---------|-------------------------------------------------------| | `e` | `E`: element to search for
| | `index` | `int`: index to start searching backwards from
| | Returns || |-------|----------------------------------------------------------------------------------------------------------------------------------------------| | `int` | 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](https://developer.android.com/reference/java/lang/IndexOutOfBoundsException) | if the specified index is greater than or equal to the current size of this list | ### listIterator Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public ListIterator 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](https://developer.android.com/reference/java/util/ListIterator#next()). An initial call to[previous](https://developer.android.com/reference/java/util/ListIterator#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.
| Parameters || |---------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | `index` | `int`: index of the first element to be returned from the list iterator (by a call to[next](https://developer.android.com/reference/java/util/ListIterator#next()))
| | Returns || |-------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------| | [ListIterator](https://developer.android.com/reference/java/util/ListIterator)`` | a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list
| | Throws || |----------------------------------------------------------------------------------------------------------|---| | [IndexOutOfBoundsException](https://developer.android.com/reference/java/lang/IndexOutOfBoundsException) | | ### listIterator Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public ListIterator 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.
| Returns || |-------------------------------------------------------------------------------------|----------------------------------------------------------------------------| | [ListIterator](https://developer.android.com/reference/java/util/ListIterator)`` | a list iterator over the elements in this list (in proper sequence)
| ### remove Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` 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.
| Parameters || |---------|------------------------------------------------------| | `index` | `int`: the index of the element to be removed
| | Returns || |-----|---------------------------------------------------------| | `E` | the element previously at the specified position
| | Throws || |----------------------------------------------------------------------------------------------------------|---| | [IndexOutOfBoundsException](https://developer.android.com/reference/java/lang/IndexOutOfBoundsException) | | ### remove Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` 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`Objects.equals(o, 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).
| Parameters || |-----|-------------------------------------------------------------------| | `o` | `Object`: element to be removed from this list, if present
| | Returns || |-----------|-----------------------------------------------------------| | `boolean` | `true`if this list contained the specified element
| ### removeAll Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` 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.
| Parameters || |-----|----------------------------------------------------------------------------------| | `c` | `Collection`: collection containing elements to be removed from this list
| | Returns || |-----------|-----------------------------------------------------------| | `boolean` | `true`if this list changed as a result of the call
| | Throws || |------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | [ClassCastException](https://developer.android.com/reference/java/lang/ClassCastException) | if the class of an element of this list is incompatible with the specified collection ([optional](https://reference/java/util/Collection.html#optional-restrictions)) | | [NullPointerException](https://developer.android.com/reference/java/lang/NullPointerException) | if this list contains a null element and the specified collection does not permit null elements ([optional](https://reference/java/util/Collection.html#optional-restrictions)), or if the specified collection is null | **See also:** - [remove(Object)](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#remove(java.lang.Object)) ### removeFirst Added in[API level 35](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public E removeFirst () ``` Removes and returns the first element of this collection (optional operation).
| Returns || |-----|----------------------------| | `E` | the removed element
| | Throws || |----------------------------------------------------------------------------------------------------|---| | [NoSuchElementException](https://developer.android.com/reference/java/util/NoSuchElementException) | | ### removeIf Added in[API level 24](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public boolean removeIf (Predicate filter) ``` 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.
| Parameters || |----------|-------------------------------------------------------------------------------| | `filter` | `Predicate`: a predicate which returns`true`for elements to be removed
| | Returns || |-----------|-------------------------------------------| | `boolean` | `true`if any elements were removed
| | Throws || |------------------------------------------------------------------------------------------------|---| | [NullPointerException](https://developer.android.com/reference/java/lang/NullPointerException) | | ### removeLast Added in[API level 35](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public E removeLast () ``` Removes and returns the last element of this collection (optional operation).
| Returns || |-----|----------------------------| | `E` | the removed element
| | Throws || |----------------------------------------------------------------------------------------------------|---| | [NoSuchElementException](https://developer.android.com/reference/java/util/NoSuchElementException) | | ### replaceAll Added in[API level 24](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public void replaceAll (UnaryOperator operator) ``` 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.
| Parameters || |------------|---------------------------------------------------------------| | `operator` | `UnaryOperator`: the operator to apply to each element
| ### retainAll Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` 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.
| Parameters || |-----|---------------------------------------------------------------------------------| | `c` | `Collection`: collection containing elements to be retained in this list
| | Returns || |-----------|-----------------------------------------------------------| | `boolean` | `true`if this list changed as a result of the call
| | Throws || |------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | [ClassCastException](https://developer.android.com/reference/java/lang/ClassCastException) | if the class of an element of this list is incompatible with the specified collection ([optional](https://reference/java/util/Collection.html#optional-restrictions)) | | [NullPointerException](https://developer.android.com/reference/java/lang/NullPointerException) | if this list contains a null element and the specified collection does not permit null elements ([optional](https://reference/java/util/Collection.html#optional-restrictions)), or if the specified collection is null | **See also:** - [remove(Object)](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#remove(java.lang.Object)) ### reversed Added in[API level 35](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public List reversed () ``` Returns a reverse-ordered[view](https://developer.android.com/reference/java/util/concurrent/Collection#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.
| Returns || |---------------------------------------------------------------------|--------------------------------------------------------------| | [List](https://developer.android.com/reference/java/util/List)`` | a reverse-ordered view of this collection, as a`List`
| ### set Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public E set (int index, E element) ``` Replaces the element at the specified position in this list with the specified element.
| Parameters || |-----------|------------------------------------------------------------| | `index` | `int`: index of the element to replace
| | `element` | `E`: element to be stored at the specified position
| | Returns || |-----|---------------------------------------------------------| | `E` | the element previously at the specified position
| | Throws || |----------------------------------------------------------------------------------------------------------|---| | [IndexOutOfBoundsException](https://developer.android.com/reference/java/lang/IndexOutOfBoundsException) | | ### size Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public int size () ``` Returns the number of elements in this list.
| Returns || |-------|--------------------------------------------| | `int` | the number of elements in this list
| ### sort Added in[API level 24](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public void sort (Comparator c) ``` Sorts this list according to the order induced by the specified[Comparator](https://developer.android.com/reference/java/util/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](https://developer.android.com/reference/java/lang/Comparable)interface and the elements'[natural ordering](https://developer.android.com/reference/java/lang/Comparable)should be used. This list must be modifiable, but need not be resizable. For apps running on and targeting Android versions greater than Nougat (API level`> 25`),[Collections.sort(List)](https://developer.android.com/reference/java/util/Collections#sort(java.util.List))delegates to this method. Such apps must not call[Collections.sort(List)](https://developer.android.com/reference/java/util/Collections#sort(java.util.List))from this method. Instead, prefer not overriding this method at all. If you must override it, consider this implementation: ``` @Override public void sort(Comparator c) { Object[] elements = toArray(); Arrays.sort(elements, c); ListIterator iterator = (ListIterator) listIterator(); for (Object element : elements) { iterator.next(); iterator.set((E) element); } } ```

| Parameters || |-----|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | `c` | `Comparator`: the`Comparator`used to compare list elements. A`null`value indicates that the elements'[natural ordering](https://developer.android.com/reference/java/lang/Comparable)should be used
| ### spliterator Added in[API level 24](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public Spliterator spliterator () ``` Returns a[Spliterator](https://developer.android.com/reference/java/util/Spliterator)over the elements in this list. The`Spliterator`reports[Spliterator.IMMUTABLE](https://developer.android.com/reference/java/util/Spliterator#IMMUTABLE),[Spliterator.ORDERED](https://developer.android.com/reference/java/util/Spliterator#ORDERED),[Spliterator.SIZED](https://developer.android.com/reference/java/util/Spliterator#SIZED), and[Spliterator.SUBSIZED](https://developer.android.com/reference/java/util/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.
| Returns || |-----------------------------------------------------------------------------------|-----------------------------------------------------| | [Spliterator](https://developer.android.com/reference/java/util/Spliterator)`` | a`Spliterator`over the elements in this list
| ### subList Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public List 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.
| Parameters || |-------------|--------------------------------------------------------| | `fromIndex` | `int`: low endpoint (inclusive) of the subList
| | `toIndex` | `int`: high endpoint (exclusive) of the subList
| | Returns || |---------------------------------------------------------------------|-------------------------------------------------------| | [List](https://developer.android.com/reference/java/util/List)`` | a view of the specified range within this list
| | Throws || |----------------------------------------------------------------------------------------------------------|---| | [IndexOutOfBoundsException](https://developer.android.com/reference/java/lang/IndexOutOfBoundsException) | | ### toArray Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` 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.
| Returns || |----------------------------------------------------------------------|----------------------------------------------------------| | [Object[]](https://developer.android.com/reference/java/lang/Object) | an array containing all the elements in this list
| ### toArray Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` public 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()](https://developer.android.com/reference/java/util/concurrent/CopyOnWriteArrayList#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()`.

| Parameters || |-----|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | `a` | `T`: 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 || |-------|----------------------------------------------------------| | `T[]` | an array containing all the elements in this list
| | Throws || |------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------| | [ArrayStoreException](https://developer.android.com/reference/java/lang/ArrayStoreException) | if the runtime type of the specified array is not a supertype of the runtime type of every element in this list | | [NullPointerException](https://developer.android.com/reference/java/lang/NullPointerException) | if the specified array is null | ### toString Added in[API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) ``` 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)](https://developer.android.com/reference/java/lang/String#valueOf(java.lang.Object)).
| Returns || |--------------------------------------------------------------------|---------------------------------------------| | [String](https://developer.android.com/reference/java/lang/String) | a string representation of this list
|