Added in API level 1

ArrayList

open class ArrayList<E : Any!> : AbstractList<E>, Cloneable, RandomAccess, Serializable, MutableList<E>

kotlin.Any
↳	java.util.AbstractCollection<E>
	↳	java.util.AbstractList<E>
		↳	java.util.ArrayList

Resizable-array implementation of the List interface. Implements all optional list operations, and permits all elements, including null. In addition to implementing the List interface, this class provides methods to manipulate the size of the array that is used internally to store the list. (This class is roughly equivalent to Vector, except that it is unsynchronized.)

The size, isEmpty, get, set, iterator, and listIterator operations run in constant time. The add operation runs in amortized constant time, that is, adding n elements requires O(n) time. All of the other operations run in linear time (roughly speaking). The constant factor is low compared to that for the LinkedList implementation.

Each ArrayList instance has a capacity. The capacity is the size of the array used to store the elements in the list. It is always at least as large as the list size. As elements are added to an ArrayList, its capacity grows automatically. The details of the growth policy are not specified beyond the fact that adding an element has constant amortized time cost.

An application can increase the capacity of an ArrayList instance before adding a large number of elements using the ensureCapacity operation. This may reduce the amount of incremental reallocation.

Note that this implementation is not synchronized. If multiple threads access an ArrayList instance concurrently, and at least one of the threads modifies the list structurally, it must be synchronized externally. (A structural modification is any operation that adds or deletes one or more elements, or explicitly resizes the backing array; merely setting the value of an element is not a structural modification.) This is typically accomplished by synchronizing on some object that naturally encapsulates the list. If no such object exists, the list should be "wrapped" using the Collections.synchronizedList method. This is best done at creation time, to prevent accidental unsynchronized access to the list:

List list = Collections.synchronizedList(new ArrayList(...));

The iterators returned by this class's #iterator() and listIterator methods are fail-fast: if the list is structurally modified at any time after the iterator is created, in any way except through the iterator's own remove or add methods, the iterator will throw a ConcurrentModificationException. Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.

Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally speaking, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification. Fail-fast iterators throw ConcurrentModificationException on a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the fail-fast behavior of iterators should be used only to detect bugs.

This class is a member of the Java Collections Framework.

Summary

Public constructors
ArrayList() Constructs an empty list with an initial capacity of ten.
ArrayList(initialCapacity: Int) Constructs an empty list with the specified initial capacity.
ArrayList(c: MutableCollection<out E>) Constructs a list containing the elements of the specified collection, in the order they are returned by the collection's iterator.

Public methods
open Boolean	add(element: E) Appends the specified element to the end of this list.
open Unit	add(index: Int, element: E) Inserts the specified element at the specified position in this list.
open Boolean	addAll(index: Int, elements: Collection<E>) Inserts all of the elements in the specified collection into this list, starting at the specified position.
open Boolean	addAll(elements: Collection<E>) 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.
open Unit	addFirst(element: E) Adds an element as the first element of this collection (optional operation).
open Unit	addLast(element: E) Adds an element as the last element of this collection (optional operation).
open Unit	clear() Removes all of the elements from this list.
open Any	clone() Returns a shallow copy of this ArrayList instance.
open Boolean	contains(element: E) Returns true if this list contains the specified element.
open Boolean	contains(element: E) Returns true if this list contains the specified element.
open Unit	ensureCapacity(minCapacity: Int) Increases the capacity of this ArrayList instance, if necessary, to ensure that it can hold at least the number of elements specified by the minimum capacity argument.
open Boolean	equals(other: Any?) Compares the specified object with this list for equality.
open Unit	forEach(action: Consumer<in E>)
open E	get(index: Int) Returns the element at the specified position in this list.
open E	getFirst() Gets the first element of this collection.
open E	getLast() Gets the last element of this collection.
open Int	hashCode() Returns the hash code value for this list.
open Int	indexOf(element: E) Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element.
open Int	indexOf(element: E) Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element.
open Boolean	isEmpty() Returns true if this list contains no elements.
open MutableIterator<E>	iterator() Returns an iterator over the elements in this list in proper sequence.
open Int	lastIndexOf(element: E) Returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element.
open Int	lastIndexOf(element: E) Returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element.
open MutableListIterator<E>	listIterator() Returns a list iterator over the elements in this list (in proper sequence).
open MutableListIterator<E>	listIterator(index: Int) Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list.
open Boolean	remove(element: E) Removes the first occurrence of the specified element from this list, if it is present.
open Boolean	remove(element: E) Removes the first occurrence of the specified element from this list, if it is present.
open Boolean	removeAll(elements: Collection<E>) Removes from this list all of its elements that are contained in the specified collection.
open E	removeAt(index: Int) Removes the element at the specified position in this list.
open E	removeFirst() Removes and returns the first element of this collection (optional operation).
open Boolean	removeIf(filter: Predicate<in E>)
open E	removeLast() Removes and returns the last element of this collection (optional operation).
open Unit	replaceAll(operator: UnaryOperator<E>)
open Boolean	retainAll(elements: Collection<E>) Retains only the elements in this list that are contained in the specified collection.
open E	set(index: Int, element: E) Replaces the element at the specified position in this list with the specified element.
open Unit	sort(c: Comparator<in E>?)
open Spliterator<E>	spliterator() Creates a late-binding and fail-fast Spliterator over the elements in this list.
open MutableList<E>	subList(fromIndex: Int, toIndex: Int) Returns a view of the portion of this list between the specified fromIndex, inclusive, and toIndex, exclusive.
open Array<Any!>	toArray() Returns an array containing all of the elements in this list in proper sequence (from first to last element).
open Array<T>	toArray(a: Array<T>) 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.
open Unit	trimToSize() Trims the capacity of this ArrayList instance to be the list's current size.

Protected methods
open Unit	removeRange(fromIndex: Int, toIndex: Int) Removes from this list all of the elements whose index is between fromIndex, inclusive, and toIndex, exclusive.

Inherited functions

From class AbstractCollection Boolean addAll(elements: Collection<E>) Adds all of the elements in the specified collection to this collection (optional operation). The behavior of this operation is undefined if the specified collection is modified while the operation is in progress. (This implies that the behavior of this call is undefined if the specified collection is this collection, and this collection is nonempty.) If the specified collection has a defined encounter order, processing of its elements generally occurs in that order. Boolean contains(element: E?) Returns true if this collection contains the specified element. More formally, returns true if and only if this collection contains at least one element e such that Objects.equals(o, e). Boolean containsAll(elements: Collection<E>) Returns true if this collection contains all of the elements in the specified collection. Boolean isEmpty() Returns true if this collection contains no elements. Boolean remove(element: E?) Removes a single instance of the specified element from this collection, if it is present (optional operation). More formally, removes an element e such that Objects.equals(o, e), if this collection contains one or more such elements. Returns true if this collection contained the specified element (or equivalently, if this collection changed as a result of the call). Boolean removeAll(elements: Collection<E>) Removes all of this collection's elements that are also contained in the specified collection (optional operation). After this call returns, this collection will contain no elements in common with the specified collection. Boolean retainAll(elements: Collection<E>) Retains only the elements in this collection that are contained in the specified collection (optional operation). In other words, removes from this collection all of its elements that are not contained in the specified collection. Array<Any!> toArray() Returns an array containing all of the elements in this collection. If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order. The returned array's runtime component type is Object. The returned array will be "safe" in that no references to it are maintained by this collection. (In other words, this method must allocate a new array even if this collection is backed by an array). The caller is thus free to modify the returned array. Array<T> toArray(a: Array<T>) Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array. If the collection 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 collection. If this collection fits in the specified array with room to spare (i.e., the array has more elements than this collection), the element in the array immediately following the end of the collection is set to null. (This is useful in determining the length of this collection only if the caller knows that this collection does not contain any null elements.) If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order. String toString() Returns a string representation of this collection. The string representation consists of a list of the collection'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).

Properties
open Int	size Returns the number of elements in this list.

Inherited properties
From class AbstractList Int modCount The number of times this list has been structurally modified. Structural modifications are those that change the size of the list, or otherwise perturb it in such a fashion that iterations in progress may yield incorrect results. This field is used by the iterator and list iterator implementation returned by the iterator and listIterator methods. If the value of this field changes unexpectedly, the iterator (or list iterator) will throw a ConcurrentModificationException in response to the next, remove, previous, set or add operations. This provides fail-fast behavior, rather than non-deterministic behavior in the face of concurrent modification during iteration. Use of this field by subclasses is optional. If a subclass wishes to provide fail-fast iterators (and list iterators), then it merely has to increment this field in its add(int, E) and remove(int) methods (and any other methods that it overrides that result in structural modifications to the list). A single call to add(int, E) or remove(int) must add no more than one to this field, or the iterators (and list iterators) will throw bogus ConcurrentModificationExceptions. If an implementation does not wish to provide fail-fast iterators, this field may be ignored.
From class AbstractCollection Int size

Public constructors

ArrayList

Added in API level 1

ArrayList()

Constructs an empty list with an initial capacity of ten.

ArrayList

Added in API level 1

ArrayList(initialCapacity: Int)

Constructs an empty list with the specified initial capacity.

Parameters
initialCapacity	Int: the initial capacity of the list

Exceptions
java.lang.IllegalArgumentException	if the specified initial capacity is negative

ArrayList

Added in API level 1

ArrayList(c: MutableCollection<out E>)

Constructs a list containing the elements of the specified collection, in the order they are returned by the collection's iterator.

Parameters
c	MutableCollection<out E>: the collection whose elements are to be placed into this list

Exceptions
java.lang.NullPointerException	if the specified collection is null

Public methods

add

Added in API level 1

open fun add(element: E): Boolean

Appends the specified element to the end of this list.

Parameters
e	element to be appended to this list

Return
Boolean	true (as specified by Collection.add)

Exceptions
java.lang.UnsupportedOperationException	if the add operation is not supported by this list
java.lang.ClassCastException	if the class of the specified element prevents it from being added to this list
java.lang.NullPointerException	if the specified element is null and this list does not permit null elements
java.lang.IllegalArgumentException	if some property of this element prevents it from being added to this list
java.lang.IllegalStateException	if the element cannot be added at this time due to insertion restrictions

add

Added in API level 1

open fun add(
    index: Int, 
    element: E
): Unit

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

Exceptions
java.lang.UnsupportedOperationException	if the add operation is not supported by this list
java.lang.ClassCastException	if the class of the specified element prevents it from being added to this list
java.lang.NullPointerException	if the specified element is null and this list does not permit null elements
java.lang.IllegalArgumentException	if some property of the specified element prevents it from being added to this list
java.lang.IndexOutOfBoundsException	if the index is out of range (index < 0 || index > size())

addAll

Added in API level 1

open fun addAll(
    index: Int, 
    elements: Collection<E>
): Boolean

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 the 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 containing elements to be added to this list

Return
Boolean	true if this list changed as a result of the call

Exceptions
java.lang.UnsupportedOperationException	if the addAll operation is not supported by this list
java.lang.ClassCastException	if the class of an element of the specified collection prevents it from being added to this list
java.lang.NullPointerException	if the specified collection is null
java.lang.IllegalArgumentException	if some property of an element of the specified collection prevents it from being added to this list
java.lang.IndexOutOfBoundsException	if the index is out of range (index < 0 || index > size())

addAll

Added in API level 1

open fun addAll(elements: Collection<E>): Boolean

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. The behavior of this operation is undefined if the specified collection is modified while the operation is in progress. (This implies that the behavior of this call is undefined if the specified collection is this list, and this list is nonempty.)

Parameters
c	collection containing elements to be added to this list

Return
Boolean	true if this list changed as a result of the call

Exceptions
java.lang.UnsupportedOperationException	if the addAll operation is not supported by this list
java.lang.ClassCastException	if the class of an element of the specified collection prevents it from being added to this list
java.lang.NullPointerException	if the specified collection is null
java.lang.IllegalArgumentException	if some property of an element of the specified collection prevents it from being added to this list
java.lang.IllegalStateException	if not all the elements can be added at this time due to insertion restrictions

addFirst

Added in API level 35

open fun addFirst(element: E): Unit

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	the element to be added

Exceptions
java.lang.NullPointerException	if the specified element is null and this collection does not permit null elements
java.lang.UnsupportedOperationException	if this collection implementation does not support this operation

addLast

Added in API level 35

open fun addLast(element: E): Unit

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	the element to be added.

Exceptions
java.lang.NullPointerException	if the specified element is null and this collection does not permit null elements
java.lang.UnsupportedOperationException	if this collection implementation does not support this operation

clear

Added in API level 1

open fun clear(): Unit

Removes all of the elements from this list. The list will be empty after this call returns.

Exceptions
java.lang.UnsupportedOperationException	if the clear operation is not supported by this list

clone

Added in API level 1

open fun clone(): Any

Returns a shallow copy of this ArrayList instance. (The elements themselves are not copied.)

Return
Any	a clone of this ArrayList instance

Exceptions
java.lang.CloneNotSupportedException	if the object's class does not support the Cloneable interface. Subclasses that override the clone method can also throw this exception to indicate that an instance cannot be cloned.

contains

Added in API level 1

open fun contains(element: E): Boolean

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	element whose presence in this list is to be tested

Return
Boolean	true if this list contains the specified element

Exceptions
java.lang.ClassCastException	if the type of the specified element is incompatible with this list (optional)
java.lang.NullPointerException	if the specified element is null and this list does not permit null elements (optional)

contains

Added in API level 1

open fun contains(element: E): Boolean

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	element whose presence in this list is to be tested

Return
Boolean	true if this list contains the specified element

Exceptions
java.lang.ClassCastException	if the type of the specified element is incompatible with this list (optional)
java.lang.NullPointerException	if the specified element is null and this list does not permit null elements (optional)

ensureCapacity

Added in API level 1

open fun ensureCapacity(minCapacity: Int): Unit

Increases the capacity of this ArrayList instance, if necessary, to ensure that it can hold at least the number of elements specified by the minimum capacity argument.

Parameters
minCapacity	Int: the desired minimum capacity

equals

Added in API level 1

open fun equals(other: Any?): Boolean

Compares the specified object with this list for equality. Returns true if and only if the specified object is also a list, both lists have the same size, and all corresponding pairs of elements in the two lists are equal. (Two elements e1 and e2 are equal if (e1==null ? e2==null : e1.equals(e2)).) In other words, two lists are defined to be equal if they contain the same elements in the same order.

Parameters
obj	the reference object with which to compare.
o	the object to be compared for equality with this list

Return
Boolean	true if the specified object is equal to this list

forEach

Added in API level 24

open fun forEach(action: Consumer<in E>): Unit

Parameters
action	Consumer<in E>: The action to be performed for each element

Exceptions
java.lang.NullPointerException	if the specified action is null

get

Added in API level 1

open fun get(index: Int): E

Returns the element at the specified position in this list.

Parameters
index	Int: index of the element to return

Return
E	the element at the specified position in this list

Exceptions
java.lang.IndexOutOfBoundsException	if the index is out of range (index < 0 || index >= size())

getFirst

Added in API level 35

open fun getFirst(): E

Gets the first element of this collection.

Return
E	the retrieved element

Exceptions
java.util.NoSuchElementException	if this collection is empty

getLast

Added in API level 35

open fun getLast(): E

Gets the last element of this collection.

Return
E	the retrieved element

Exceptions
java.util.NoSuchElementException	if this collection is empty

hashCode

Added in API level 1

open fun hashCode(): Int

Returns the hash code value for this list.

Return
Int	the hash code value for this list

indexOf

Added in API level 1

open fun indexOf(element: E): Int

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	element to search for

Return
Int	the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element

Exceptions
java.lang.ClassCastException	if the type of the specified element is incompatible with this list (optional)
java.lang.NullPointerException	if the specified element is null and this list does not permit null elements (optional)

indexOf

Added in API level 1

open fun indexOf(element: E): Int

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	element to search for

Return
Int	the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element

Exceptions
java.lang.ClassCastException	if the type of the specified element is incompatible with this list (optional)
java.lang.NullPointerException	if the specified element is null and this list does not permit null elements (optional)

isEmpty

Added in API level 1

open fun isEmpty(): Boolean

Returns true if this list contains no elements.

Return
Boolean	true if this list contains no elements

iterator

Added in API level 1

open fun iterator(): MutableIterator<E>

Returns an iterator over the elements in this list in proper sequence.

The returned iterator is fail-fast.

Return
MutableIterator<E>	an iterator over the elements in this list in proper sequence

lastIndexOf

Added in API level 1

open fun lastIndexOf(element: E): Int

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	element to search for

Return
Int	the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element

Exceptions
java.lang.ClassCastException	if the type of the specified element is incompatible with this list (optional)
java.lang.NullPointerException	if the specified element is null and this list does not permit null elements (optional)

lastIndexOf

Added in API level 1

open fun lastIndexOf(element: E): Int

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	element to search for

Return
Int	the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element

Exceptions
java.lang.ClassCastException	if the type of the specified element is incompatible with this list (optional)
java.lang.NullPointerException	if the specified element is null and this list does not permit null elements (optional)

listIterator

Added in API level 1

open fun listIterator(): MutableListIterator<E>

Returns a list iterator over the elements in this list (in proper sequence).

The returned list iterator is fail-fast.

Return
MutableListIterator<E>	a list iterator over the elements in this list (in proper sequence)

See Also

• #listIterator(int)

listIterator

Added in API level 1

open fun listIterator(index: Int): MutableListIterator<E>

Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list. The specified index indicates the first element that would be returned by an initial call to next. An initial call to previous would return the element with the specified index minus one.

The returned list iterator is fail-fast.

Parameters
index	Int: index of the first element to be returned from the list iterator (by a call to next)

Return
MutableListIterator<E>	a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list

Exceptions
java.lang.IndexOutOfBoundsException	if the index is out of range (index < 0 || index > size())

remove

Added in API level 1

open fun remove(element: E): Boolean

Removes the first occurrence of the specified element from this list, if it is present. If the 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	element to be removed from this list, if present

Return
Boolean	true if this list contained the specified element

Exceptions
java.lang.ClassCastException	if the type of the specified element is incompatible with this list (optional)
java.lang.NullPointerException	if the specified element is null and this list does not permit null elements (optional)
java.lang.UnsupportedOperationException	if the remove operation is not supported by this list

remove

Added in API level 1

open fun remove(element: E): Boolean

Removes the first occurrence of the specified element from this list, if it is present. If the 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	element to be removed from this list, if present

Return
Boolean	true if this list contained the specified element

Exceptions
java.lang.ClassCastException	if the type of the specified element is incompatible with this list (optional)
java.lang.NullPointerException	if the specified element is null and this list does not permit null elements (optional)
java.lang.UnsupportedOperationException	if the remove operation is not supported by this list

removeAll

Added in API level 1

open fun removeAll(elements: Collection<E>): Boolean

Removes from this list all of its elements that are contained in the specified collection.

Parameters
c	collection containing elements to be removed from this list

Return
Boolean	true if this list changed as a result of the call

Exceptions
java.lang.UnsupportedOperationException	if the removeAll operation is not supported by this list
java.lang.ClassCastException	if the class of an element of this list is incompatible with the specified collection (optional)
java.lang.NullPointerException	if this list contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is null

See Also

• java.util.Collection#contains(Object)

removeAt

Added in API level 1

open fun removeAt(index: Int): E

Removes the element at the specified position in this list. Shifts any subsequent elements to the left (subtracts one from their indices).

Parameters
index	Int: the index of the element to be removed

Return
E	the element that was removed from the list

Exceptions
java.lang.UnsupportedOperationException	if the remove operation is not supported by this list
java.lang.IndexOutOfBoundsException	if the index is out of range (index < 0 || index >= size())

removeFirst

Added in API level 35

open fun removeFirst(): E

Removes and returns the first element of this collection (optional operation).

Return
E	the removed element

Exceptions
java.util.NoSuchElementException	if this collection is empty
java.lang.UnsupportedOperationException	if this collection implementation does not support this operation

removeIf

Added in API level 24

open fun removeIf(filter: Predicate<in E>): Boolean

Parameters
filter	Predicate<in E>: a predicate which returns true for elements to be removed

Return
Boolean	true if any elements were removed

Exceptions
java.lang.NullPointerException	if the specified filter is null
java.lang.UnsupportedOperationException	if elements cannot be removed from this collection. Implementations may throw this exception if a matching element cannot be removed or if, in general, removal is not supported.

removeLast

Added in API level 35

open fun removeLast(): E

Removes and returns the last element of this collection (optional operation).

Return
E	the removed element

Exceptions
java.util.NoSuchElementException	if this collection is empty
java.lang.UnsupportedOperationException	if this collection implementation does not support this operation

replaceAll

Added in API level 24

open fun replaceAll(operator: UnaryOperator<E>): Unit

Parameters
operator	UnaryOperator<E>: the operator to apply to each element

Exceptions
java.lang.UnsupportedOperationException	if this list is unmodifiable. Implementations may throw this exception if an element cannot be replaced or if, in general, modification is not supported
java.lang.NullPointerException	if the specified operator is null or if the operator result is a null value and this list does not permit null elements (optional)

retainAll

Added in API level 1

open fun retainAll(elements: Collection<E>): Boolean

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 containing elements to be retained in this list

Return
Boolean	true if this list changed as a result of the call

Exceptions
java.lang.UnsupportedOperationException	if the retainAll operation is not supported by this list
java.lang.ClassCastException	if the class of an element of this list is incompatible with the specified collection (optional)
java.lang.NullPointerException	if this list contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is null

See Also

• java.util.Collection#contains(Object)

set

Added in API level 1

open fun set(
    index: Int, 
    element: E
): E

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

Return
E	the element previously at the specified position

Exceptions
java.lang.UnsupportedOperationException	if the set operation is not supported by this list
java.lang.ClassCastException	if the class of the specified element prevents it from being added to this list
java.lang.NullPointerException	if the specified element is null and this list does not permit null elements
java.lang.IllegalArgumentException	if some property of the specified element prevents it from being added to this list
java.lang.IndexOutOfBoundsException	if the index is out of range (index < 0 || index >= size())

sort

Added in API level 24

open fun sort(c: Comparator<in E>?): Unit

Parameters
c	Comparator<in E>?: the Comparator used to compare list elements. A null value indicates that the elements' natural ordering should be used

Exceptions
java.lang.ClassCastException	if the list contains elements that are not mutually comparable using the specified comparator
java.lang.UnsupportedOperationException	if the list's list-iterator does not support the set operation
java.lang.IllegalArgumentException	(optional) if the comparator is found to violate the Comparator contract

spliterator

Added in API level 24

open fun spliterator(): Spliterator<E>

Creates a late-binding and fail-fast Spliterator over the elements in this list.

The Spliterator reports Spliterator.SIZED, Spliterator.SUBSIZED, and Spliterator.ORDERED. Overriding implementations should document the reporting of additional characteristic values.

Return
Spliterator<E>	a Spliterator over the elements in this list

subList

Added in API level 1

open fun subList(
    fromIndex: Int, 
    toIndex: Int
): MutableList<E>

Returns a view of the portion of this list between the specified fromIndex, inclusive, and toIndex, exclusive. (If fromIndextoIndex are equal, the returned list is empty.) The returned list is backed by this list, so non-structural changes in the returned list are reflected in this list, and vice-versa. The returned list supports all of the optional list operations.

This method eliminates the need for explicit range operations (of the sort that commonly exist for arrays). Any operation that expects a list can be used as a range operation by passing a subList view instead of a whole list. For example, the following idiom removes a range of elements from a list:

list.subList(from, to).clear();
  

Similar idioms may be constructed for indexOf(java.lang.Object) and lastIndexOf(java.lang.Object), and all of the algorithms in the Collections class can be applied to a subList.

The semantics of the list returned by this method become undefined if the backing list (i.e., this list) is structurally modified in any way other than via the returned list. (Structural modifications are those that change the size of this list, or otherwise perturb it in such a fashion that iterations in progress may yield incorrect results.)

Parameters
fromIndex	Int: low endpoint (inclusive) of the subList
toIndex	Int: high endpoint (exclusive) of the subList

Return
MutableList<E>	a view of the specified range within this list

Exceptions
java.lang.IndexOutOfBoundsException	if an endpoint index value is out of range (fromIndex < 0 || toIndex > size)
java.lang.IllegalArgumentException	if the endpoint indices are out of order (fromIndex > toIndex)

toArray

Added in API level 1

open fun toArray(): Array<Any!>

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.

Return
Array<Any!>	an array containing all of the elements in this list in proper sequence

toArray

Added in API level 1

open fun <T : Any!> toArray(a: Array<T>): Array<T>

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 the list fits in the specified array with room to spare (i.e., the array has more elements than the list), the element in the array immediately following the end of the collection is set to null. (This is useful in determining the length of the list only if the caller knows that the list does not contain any null elements.)

Parameters
<T>	the component type of the array to contain the collection
a	Array<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.

Return
Array<T>	an array containing the elements of the list

Exceptions
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
java.lang.NullPointerException	if the specified array is null

trimToSize

Added in API level 1

open fun trimToSize(): Unit

Trims the capacity of this ArrayList instance to be the list's current size. An application can use this operation to minimize the storage of an ArrayList instance.

Protected methods

removeRange

Added in API level 1

protected open fun removeRange(
    fromIndex: Int, 
    toIndex: Int
): Unit

Removes from this list all of the elements whose index is between fromIndex, inclusive, and toIndex, exclusive. Shifts any succeeding elements to the left (reduces their index). This call shortens the list by (toIndex - fromIndex) elements. (If toIndex==fromIndex, this operation has no effect.)

Parameters
fromIndex	Int: index of first element to be removed
toIndex	Int: index after last element to be removed

Exceptions
java.lang.IndexOutOfBoundsException	if fromIndex or toIndex is out of range (fromIndex < 0 || toIndex > size() || toIndex < fromIndex)

Properties

size

Added in API level 1

open val size: Int

Returns the number of elements in this list.

Return
Int	the number of elements in this list