Since: API Level 1

public class

ArrayList

extends AbstractList<E>
implements Serializable Cloneable RandomAccess

java.lang.Object
↳	java.util.AbstractCollection<E>
	↳	java.util.AbstractList<E>
		↳	java.util.ArrayList<E>

Class Overview

ArrayList is an implementation of List, backed by an array. All optional operations including adding, removing, and replacing elements are supported.

All elements are permitted, including null.

This class is a good choice as your default List implementation. Vector synchronizes all operations, but not necessarily in a way that's meaningful to your application: synchronizing each call to get, for example, is not equivalent to synchronizing the list and iterating over it (which is probably what you intended). CopyOnWriteArrayList is intended for the special case of very high concurrency, frequent traversals, and very rare mutations.

Summary

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Inherited Fields

From class java.util.AbstractList

Public Constructors
	ArrayList(int capacity) Constructs a new instance of `ArrayList` with the specified initial capacity.
	ArrayList() Constructs a new `ArrayList` instance with zero initial capacity.
	ArrayList(Collection<? extends E> collection) Constructs a new instance of `ArrayList` containing the elements of the specified collection.

Public Methods
boolean	add(E object) Adds the specified object at the end of this `ArrayList`.
void	add(int index, E object) Inserts the specified object into this `ArrayList` at the specified location.
boolean	addAll(Collection<? extends E> collection) Adds the objects in the specified collection to this `ArrayList`.
boolean	addAll(int index, Collection<? extends E> collection) Inserts the objects in the specified collection at the specified location in this List.
void	clear() Removes all elements from this `ArrayList`, leaving it empty.
Object	clone() Returns a new `ArrayList` with the same elements, the same size and the same capacity as this `ArrayList`.
boolean	contains(Object object) Searches this `ArrayList` for the specified object.
void	ensureCapacity(int minimumCapacity) Ensures that after this operation the `ArrayList` can hold the specified number of elements without further growing.
boolean	equals(Object o) Compares the specified object to this list and return true if they are equal.
E	get(int index) Returns the element at the specified location in this list.
int	hashCode() Returns the hash code of this list.
int	indexOf(Object object) Searches this list for the specified object and returns the index of the first occurrence.
boolean	isEmpty() Returns if this `Collection` contains no elements.
Iterator<E>	iterator() Returns an iterator on the elements of this list.
int	lastIndexOf(Object object) Searches this list for the specified object and returns the index of the last occurrence.
E	remove(int index) Removes the object at the specified location from this list.
boolean	remove(Object object) Removes one instance of the specified object from this `Collection` if one is contained (optional).
E	set(int index, E object) Replaces the element at the specified location in this `ArrayList` with the specified object.
int	size() Returns the number of elements in this `ArrayList`.
<T> T[]	toArray(T[] contents) Returns an array containing all elements contained in this `ArrayList`.
Object[]	toArray() Returns a new array containing all elements contained in this `ArrayList`.
void	trimToSize() Sets the capacity of this `ArrayList` to be the same as the current size.

Protected Methods
void	removeRange(int fromIndex, int toIndex) Removes the objects in the specified range from the start to the end index minus one.

[Expand]

Inherited Methods

From class java.util.AbstractList

boolean	add(E object) Adds the specified object at the end of this List.
void	add(int location, E object) Inserts the specified object into this List at the specified location.
boolean	addAll(int location, Collection<? extends E> collection) Inserts the objects in the specified Collection at the specified location in this List.
void	clear() Removes all elements from this list, leaving it empty.
boolean	equals(Object object) Compares the specified object to this list and return true if they are equal.
abstract E	get(int location) Returns the element at the specified location in this list.
int	hashCode() Returns the hash code of this list.
int	indexOf(Object object) Searches this list for the specified object and returns the index of the first occurrence.
Iterator<E>	iterator() Returns an iterator on the elements of this list.
int	lastIndexOf(Object object) Searches this list for the specified object and returns the index of the last occurrence.
ListIterator<E>	listIterator(int location) Returns a list iterator on the elements of this list.
ListIterator<E>	listIterator() Returns a ListIterator on the elements of this list.
E	remove(int location) Removes the object at the specified location from this list.
void	removeRange(int start, int end) Removes the objects in the specified range from the start to the end index minus one.
E	set(int location, E object) Replaces the element at the specified location in this list with the specified object.
List<E>	subList(int start, int end) Returns a part of consecutive elements of this list as a view.

From class java.util.AbstractCollection

boolean	add(E object) Attempts to add `object` to the contents of this `Collection` (optional).
boolean	addAll(Collection<? extends E> collection) Attempts to add all of the objects contained in `collection` to the contents of this `Collection` (optional).
void	clear() Removes all elements from this `Collection`, leaving it empty (optional).
boolean	contains(Object object) Tests whether this `Collection` contains the specified object.
boolean	containsAll(Collection<?> collection) Tests whether this `Collection` contains all objects contained in the specified `Collection`.
boolean	isEmpty() Returns if this `Collection` contains no elements.
abstract Iterator<E>	iterator() Returns an instance of `Iterator` that may be used to access the objects contained by this `Collection`.
boolean	remove(Object object) Removes one instance of the specified object from this `Collection` if one is contained (optional).
boolean	removeAll(Collection<?> collection) Removes all occurrences in this `Collection` of each object in the specified `Collection` (optional).
boolean	retainAll(Collection<?> collection) Removes all objects from this `Collection` that are not also found in the `Collection` passed (optional).
abstract int	size() Returns a count of how many objects this `Collection` contains.
<T> T[]	toArray(T[] contents) Returns an array containing all elements contained in this `Collection`.
Object[]	toArray() Returns a new array containing all elements contained in this `Collection`.
String	toString() Returns the string representation of this `Collection`.

From class java.lang.Object

Object	clone() Creates and returns a copy of this `Object`.
boolean	equals(Object o) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Called before the object's memory is reclaimed by the VM.
final Class<?>	getClass() Returns the unique instance of `Class` that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the `wait()` methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the `wait()` methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait() Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object.
final void	wait(long millis, int nanos) Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object or until the specified timeout expires.
final void	wait(long millis) Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object or until the specified timeout expires.

From interface java.lang.Iterable

From interface java.util.Collection

abstract boolean	add(E object) Attempts to add `object` to the contents of this `Collection` (optional).
abstract boolean	addAll(Collection<? extends E> collection) Attempts to add all of the objects contained in `Collection` to the contents of this `Collection` (optional).
abstract void	clear() Removes all elements from this `Collection`, leaving it empty (optional).
abstract boolean	contains(Object object) Tests whether this `Collection` contains the specified object.
abstract boolean	containsAll(Collection<?> collection) Tests whether this `Collection` contains all objects contained in the specified `Collection`.
abstract boolean	equals(Object object) Compares the argument to the receiver, and returns true if they represent the same object using a class specific comparison.
abstract int	hashCode() Returns an integer hash code for the receiver.
abstract boolean	isEmpty() Returns if this `Collection` contains no elements.
abstract Iterator<E>	iterator() Returns an instance of `Iterator` that may be used to access the objects contained by this `Collection`.
abstract boolean	remove(Object object) Removes one instance of the specified object from this `Collection` if one is contained (optional).
abstract boolean	removeAll(Collection<?> collection) Removes all occurrences in this `Collection` of each object in the specified `Collection` (optional).
abstract boolean	retainAll(Collection<?> collection) Removes all objects from this `Collection` that are not also found in the `Collection` passed (optional).
abstract int	size() Returns a count of how many objects this `Collection` contains.
abstract <T> T[]	toArray(T[] array) Returns an array containing all elements contained in this `Collection`.
abstract Object[]	toArray() Returns a new array containing all elements contained in this `Collection`.

From interface java.util.List

abstract boolean	add(E object) Adds the specified object at the end of this `List`.
abstract void	add(int location, E object) Inserts the specified object into this `List` at the specified location.
abstract boolean	addAll(Collection<? extends E> collection) Adds the objects in the specified collection to the end of this `List`.
abstract boolean	addAll(int location, Collection<? extends E> collection) Inserts the objects in the specified collection at the specified location in this `List`.
abstract void	clear() Removes all elements from this `List`, leaving it empty.
abstract boolean	contains(Object object) Tests whether this `List` contains the specified object.
abstract boolean	containsAll(Collection<?> collection) Tests whether this `List` contains all objects contained in the specified collection.
abstract boolean	equals(Object object) Compares the given object with the `List`, and returns true if they represent the same object using a class specific comparison.
abstract E	get(int location) Returns the element at the specified location in this `List`.
abstract int	hashCode() Returns the hash code for this `List`.
abstract int	indexOf(Object object) Searches this `List` for the specified object and returns the index of the first occurrence.
abstract boolean	isEmpty() Returns whether this `List` contains no elements.
abstract Iterator<E>	iterator() Returns an iterator on the elements of this `List`.
abstract int	lastIndexOf(Object object) Searches this `List` for the specified object and returns the index of the last occurrence.
abstract ListIterator<E>	listIterator(int location) Returns a list iterator on the elements of this `List`.
abstract ListIterator<E>	listIterator() Returns a `List` iterator on the elements of this `List`.
abstract E	remove(int location) Removes the object at the specified location from this `List`.
abstract boolean	remove(Object object) Removes the first occurrence of the specified object from this `List`.
abstract boolean	removeAll(Collection<?> collection) Removes all occurrences in this `List` of each object in the specified collection.
abstract boolean	retainAll(Collection<?> collection) Removes all objects from this `List` that are not contained in the specified collection.
abstract E	set(int location, E object) Replaces the element at the specified location in this `List` with the specified object.
abstract int	size() Returns the number of elements in this `List`.
abstract List<E>	subList(int start, int end) Returns a `List` of the specified portion of this `List` from the given start index to the end index minus one.
abstract <T> T[]	toArray(T[] array) Returns an array containing all elements contained in this `List`.
abstract Object[]	toArray() Returns an array containing all elements contained in this `List`.

Public Constructors

public ArrayList (int capacity)

Since: API Level 1

Constructs a new instance of ArrayList with the specified initial capacity.

Parameters

capacity	the initial capacity of this `ArrayList`.

public ArrayList ()

Since: API Level 1

Constructs a new ArrayList instance with zero initial capacity.

public ArrayList (Collection<? extends E> collection)

Since: API Level 1

Constructs a new instance of ArrayList containing the elements of the specified collection.

Parameters

collection	the collection of elements to add.

Public Methods

public boolean add (E object)

Since: API Level 1

Adds the specified object at the end of this ArrayList.

Parameters

object	the object to add.

Returns

always true

public void add (int index, E object)

Since: API Level 1

Inserts the specified object into this ArrayList at the specified location. The object is inserted before any previous element at the specified location. If the location is equal to the size of this ArrayList, the object is added at the end.

Parameters

index	the index at which to insert the object.
object	the object to add.

Throws

IndexOutOfBoundsException	when `location < 0 \|\| > size()`

public boolean addAll (Collection<? extends E> collection)

Since: API Level 1

Adds the objects in the specified collection to this ArrayList.

Parameters

collection	the collection of objects.

Returns

true if this ArrayList is modified, false otherwise.

public boolean addAll (int index, Collection<? extends E> collection)

Since: API Level 1

Inserts the objects in the specified collection at the specified location in this List. The objects are added in the order they are returned from the collection's iterator.

Parameters

index	the index at which to insert.
collection	the collection of objects.

Returns

true if this ArrayList is modified, false otherwise.

Throws

IndexOutOfBoundsException	when `location < 0 \|\| > size()`

public void clear ()

Since: API Level 1

Removes all elements from this ArrayList, leaving it empty.

public Object clone ()

Since: API Level 1

Returns a new ArrayList with the same elements, the same size and the same capacity as this ArrayList.

Returns

a shallow copy of this ArrayList

public boolean contains (Object object)

Since: API Level 1

Searches this ArrayList for the specified object.

Parameters

object	the object to search for.

Returns

true if object is an element of this ArrayList, false otherwise

public void ensureCapacity (int minimumCapacity)

Since: API Level 1

Ensures that after this operation the ArrayList can hold the specified number of elements without further growing.

Parameters

minimumCapacity	the minimum capacity asked for.

public boolean equals (Object o)

Since: API Level 1

Compares the specified object to this list and return true if they are equal. Two lists are equal when they both contain the same objects in the same order.

Parameters

o	the object to compare to this object.

Returns

true if the specified object is equal to this list, false otherwise.

public E get (int index)

Since: API Level 1

Returns the element at the specified location in this list.

Parameters

index	the index of the element to return.

Returns

the element at the specified index.

public int hashCode ()

Since: API Level 1

Returns the hash code of this list. The hash code is calculated by taking each element's hashcode into account.

Returns

the hash code.

public int indexOf (Object object)

Since: API Level 1

Searches this list for the specified object and returns the index of the first occurrence.

Parameters

object	the object to search for.

Returns

the index of the first occurrence of the object, or -1 if it was not found.

public boolean isEmpty ()

Since: API Level 1

Returns if this Collection contains no elements. This implementation tests, whether size returns 0.

Returns

true if this Collection has no elements, false otherwise.

public Iterator<E> iterator ()

Since: API Level 1

Returns an iterator on the elements of this list. The elements are iterated in the same order as they occur in the list.

Returns

an iterator on the elements of this list.

public int lastIndexOf (Object object)

Since: API Level 1

Searches this list for the specified object and returns the index of the last occurrence.

Parameters

object	the object to search for.

Returns

the index of the last occurrence of the object, or -1 if the object was not found.

public E remove (int index)

Since: API Level 1

Removes the object at the specified location from this list.

Parameters

index	the index of the object to remove.

Returns

the removed object.

Throws

IndexOutOfBoundsException	when `location < 0 \|\| >= size()`

public boolean remove (Object object)

Since: API Level 1

Removes one instance of the specified object from this Collection if one is contained (optional). This implementation iterates over this Collection and tests for each element e returned by the iterator, whether e is equal to the given object. If object != null then this test is performed using object.equals(e), otherwise using object == null. If an element equal to the given object is found, then the remove method is called on the iterator and true is returned, false otherwise. If the iterator does not support removing elements, an UnsupportedOperationException is thrown.

Parameters

object	the object to remove.

Returns

true if this Collection is modified, false otherwise.

public E set (int index, E object)

Since: API Level 1

Replaces the element at the specified location in this ArrayList with the specified object.

Parameters

index	the index at which to put the specified object.
object	the object to add.

Returns

the previous element at the index.

Throws

IndexOutOfBoundsException	when `location < 0 \|\| >= size()`

public int size ()

Since: API Level 1

Returns the number of elements in this ArrayList.

Returns

the number of elements in this ArrayList.

public T[] toArray (T[] contents)

Since: API Level 1

Returns an array containing all elements contained in this ArrayList. If the specified array is large enough to hold the elements, the specified array is used, otherwise an array of the same type is created. If the specified array is used and is larger than this ArrayList, the array element following the collection elements is set to null.

Parameters

contents	the array.

Returns

an array of the elements from this ArrayList.

Throws

ArrayStoreException	when the type of an element in this `ArrayList` cannot be stored in the type of the specified array.

public Object[] toArray ()

Since: API Level 1

Returns a new array containing all elements contained in this ArrayList.

Returns

an array of the elements from this ArrayList

public void trimToSize ()

Since: API Level 1

Sets the capacity of this ArrayList to be the same as the current size.

Protected Methods

protected void removeRange (int fromIndex, int toIndex)

Since: API Level 1

Removes the objects in the specified range from the start to the end index minus one.

Parameters

fromIndex	the index at which to start removing.
toIndex	the index after the last element to remove.

Interfaces

Classes

Enums

Exceptions

Errors

ArrayList

Class Overview

Summary

Public Constructors

public ArrayList (int capacity)

Parameters

public ArrayList ()

public ArrayList (Collection<? extends E> collection)

Parameters

Public Methods

public boolean add (E object)

Parameters

Returns

public void add (int index, E object)

Parameters

Throws

public boolean addAll (Collection<? extends E> collection)

Parameters

Returns

public boolean addAll (int index, Collection<? extends E> collection)

Parameters

Returns

Throws

public void clear ()

See Also

public Object clone ()

Returns

See Also

public boolean contains (Object object)

Parameters

Returns

public void ensureCapacity (int minimumCapacity)

Parameters

public boolean equals (Object o)

Parameters

Returns

public E get (int index)

Parameters

Returns

public int hashCode ()

Returns

public int indexOf (Object object)

Parameters

Returns

public boolean isEmpty ()

Returns

public Iterator<E> iterator ()

Returns

public int lastIndexOf (Object object)

Parameters

Returns

public E remove (int index)

Parameters

Returns

Throws

public boolean remove (Object object)

Parameters

Returns

public E set (int index, E object)

Parameters

Returns

Throws

public int size ()

Returns

public T[] toArray (T[] contents)

Parameters

Returns

Throws

public Object[] toArray ()

Returns

public void trimToSize ()

See Also

Protected Methods

protected void removeRange (int fromIndex, int toIndex)

Parameters