java.util

Class ArrayList<E>

java.lang.Object

java.util.AbstractCollection<E>

java.util.AbstractList<E>

java.util.ArrayList<E>

Type Parameters:

E - The element type of this list.

All Implemented Interfaces:

Serializable, Cloneable, Iterable<E>, Collection<E>, List<E>, RandomAccess

public class ArrayList<E>
extends AbstractList<E>
implements Cloneable, Serializable, RandomAccess

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.

Since:

1.2

See Also:

Serialized Form

Field Summary

Fields inherited from class java.util.AbstractList

modCount

Constructor Summary

Constructors

Constructor and Description
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.
ArrayList(int capacity) Constructs a new instance of ArrayList with the specified initial capacity.

Method Summary

Modifier and Type	Method and Description
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).
protected void	removeRange(int fromIndex, int toIndex) Removes the objects in the specified range from the start to the end index minus one.
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.
Object[]	toArray() Returns a new array containing all elements contained in this ArrayList.
<T> T[]	toArray(T[] contents) Returns an array containing all elements contained in this ArrayList.
void	trimToSize() Sets the capacity of this ArrayList to be the same as the current size.

Methods inherited from class java.util.AbstractList

listIterator, listIterator, subList

Methods inherited from class java.util.AbstractCollection

containsAll, removeAll, retainAll, toString

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.List

containsAll, copyOf, of, of, of, of, of, of, of, of, of, of, of, of, removeAll, replaceAll, retainAll, sort, spliterator

Methods inherited from interface java.util.Collection

forEach, parallelStream, removeIf, stream, toArray

Constructor Detail

ArrayList

public ArrayList(int capacity)

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

Parameters:

capacity - the initial capacity of this ArrayList.

ArrayList

public ArrayList()

Constructs a new ArrayList instance with zero initial capacity.

ArrayList

public ArrayList(Collection<? extends E> collection)

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

Parameters:

collection - the collection of elements to add.

Method Detail

add

public boolean add(E object)

Adds the specified object at the end of this ArrayList.

Specified by:

add in interface Collection<E>

Specified by:

add in interface List<E>

Overrides:

add in class AbstractList<E>

Parameters:

object - the object to add.

Returns:

always true

add

public void add(int index,
                E object)

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.

Specified by:

add in interface List<E>

Overrides:

add in class AbstractList<E>

Parameters:

index - the index at which to insert the object.

object - the object to add.

Throws:

IndexOutOfBoundsException - when location < 0 || location > size()

addAll

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

Adds the objects in the specified collection to this ArrayList.

Specified by:

addAll in interface Collection<E>

Specified by:

addAll in interface List<E>

Overrides:

addAll in class AbstractCollection<E>

Parameters:

collection - the collection of objects.

Returns:

true if this ArrayList is modified, false otherwise.

See Also:

Collection.add(Object)

addAll

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

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

Specified by:

addAll in interface List<E>

Overrides:

addAll in class AbstractList<E>

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 || location > size()

clear

public void clear()

Removes all elements from this ArrayList, leaving it empty.

Specified by:

clear in interface Collection<E>

Specified by:

clear in interface List<E>

Overrides:

clear in class AbstractList<E>

See Also:

isEmpty(), size

clone

public Object clone()

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

Overrides:

clone in class Object

Returns:

a shallow copy of this ArrayList

See Also:

Cloneable

ensureCapacity

public void ensureCapacity(int minimumCapacity)

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

Parameters:

minimumCapacity - the minimum capacity asked for.

get

public E get(int index)

Description copied from class: AbstractList

Returns the element at the specified location in this list.

Specified by:

get in interface List<E>

Specified by:

get in class AbstractList<E>

Parameters:

index - the index of the element to return.

Returns:

the element at the specified index.

size

public int size()

Returns the number of elements in this ArrayList.

Specified by:

size in interface Collection<E>

Specified by:

size in interface List<E>

Specified by:

size in class AbstractCollection<E>

Returns:

the number of elements in this ArrayList.

isEmpty

public boolean isEmpty()

Description copied from class: AbstractCollection

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

Specified by:

isEmpty in interface Collection<E>

Specified by:

isEmpty in interface List<E>

Overrides:

isEmpty in class AbstractCollection<E>

Returns:

true if this Collection has no elements, false otherwise.

See Also:

AbstractCollection.size()

contains

public boolean contains(Object object)

Searches this ArrayList for the specified object.

Specified by:

contains in interface Collection<E>

Specified by:

contains in interface List<E>

Overrides:

contains in class AbstractCollection<E>

Parameters:

object - the object to search for.

Returns:

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

indexOf

public int indexOf(Object object)

Description copied from class: AbstractList

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

Specified by:

indexOf in interface List<E>

Overrides:

indexOf in class AbstractList<E>

Parameters:

object - the object to search for.

Returns:

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

lastIndexOf

public int lastIndexOf(Object object)

Description copied from class: AbstractList

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

Specified by:

lastIndexOf in interface List<E>

Overrides:

lastIndexOf in class AbstractList<E>

Parameters:

object - the object to search for.

Returns:

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

remove

public E remove(int index)

Removes the object at the specified location from this list.

Specified by:

remove in interface List<E>

Overrides:

remove in class AbstractList<E>

Parameters:

index - the index of the object to remove.

Returns:

the removed object.

Throws:

IndexOutOfBoundsException - when location < 0 || location >= size()

remove

public boolean remove(Object object)

Description copied from class: AbstractCollection

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.

Specified by:

remove in interface Collection<E>

Specified by:

remove in interface List<E>

Overrides:

remove in class AbstractCollection<E>

Parameters:

object - the object to remove.

Returns:

true if this Collection is modified, false otherwise.

removeRange

protected void removeRange(int fromIndex,
                           int toIndex)

Description copied from class: AbstractList

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

Overrides:

removeRange in class AbstractList<E>

Parameters:

fromIndex - the index at which to start removing.

toIndex - the index after the last element to remove.

set

public E set(int index,
             E object)

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

Specified by:

set in interface List<E>

Overrides:

set in class AbstractList<E>

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 || location >= size()

toArray

public Object[] toArray()

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

Specified by:

toArray in interface Collection<E>

Specified by:

toArray in interface List<E>

Overrides:

toArray in class AbstractCollection<E>

Returns:

an array of the elements from this ArrayList

See Also:

Arrays.asList(Object[])

toArray

public <T> T[] toArray(T[] contents)

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.

Specified by:

toArray in interface Collection<E>

Specified by:

toArray in interface List<E>

Overrides:

toArray in class AbstractCollection<E>

Type Parameters:

T - the runtime type of the array to contain the collection

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.

trimToSize

public void trimToSize()

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

See Also:

size

iterator

public Iterator<E> iterator()

Description copied from class: AbstractList

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

Specified by:

iterator in interface Iterable<E>

Specified by:

iterator in interface Collection<E>

Specified by:

iterator in interface List<E>

Overrides:

iterator in class AbstractList<E>

Returns:

an iterator on the elements of this list.

See Also:

Iterator

hashCode

public int hashCode()

Description copied from class: AbstractList

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

Specified by:

hashCode in interface Collection<E>

Specified by:

hashCode in interface List<E>

Overrides:

hashCode in class AbstractList<E>

Returns:

the hash code.

See Also:

AbstractList.equals(java.lang.Object), List.hashCode()

equals

public boolean equals(Object o)

Description copied from class: AbstractList

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.

Specified by:

equals in interface Collection<E>

Specified by:

equals in interface List<E>

Overrides:

equals in class AbstractList<E>

Parameters:

o - the object to compare to this object.

Returns:

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

See Also:

AbstractList.hashCode()