java.lang.Object
java.util.AbstractCollection<E>
java.util.AbstractList<E>
java.util.ArrayList<E>
public class ArrayList<E>
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 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.
Collection, List, LinkedList, Vector, Collections.synchronizedList(List), Serialized Form
ArrayList()
ArrayList(Collection<? extends E> c)
ArrayList(int initialCapacity)
boolean add(E o)
void add(int index, E element)
boolean addAll(Collection<? extends E> c)
boolean addAll(int index, Collection<? extends E> c)
void clear()
Object clone()
boolean contains(Object elem)
void ensureCapacity(int minCapacity)
E get(int index)
int indexOf(Object elem)
boolean isEmpty()
int lastIndexOf(Object elem)
E remove(int index)
boolean remove(Object o)
protected void removeRange(int fromIndex, int toIndex)
E set(int index, E element)
int size()
Object[] toArray()
<T> T[] toArray(T[] a)
void trimToSize()
public ArrayList(int initialCapacity)
initialCapacity - the initial capacity of the list.
IllegalArgumentException - if the specified initial capacity is negative
public ArrayList()
public ArrayList(Collection<? extends E> c)
c - the collection whose elements are to be placed into this list.
NullPointerException - if the specified collection is null.
public void trimToSize()
public void ensureCapacity(int minCapacity)
minCapacity - the desired minimum capacity.
public int size()
size in interface Collection<E>
size in interface List<E>
size in class AbstractCollection<E>
public boolean isEmpty()
isEmpty in interface Collection<E>
isEmpty in interface List<E>
isEmpty in class AbstractCollection<E>
public boolean contains(Object elem)
contains in interface Collection<E>
contains in interface List<E>
contains in class AbstractCollection<E>
elem - element whose presence in this List is to be tested.
true if the specified element is present; false otherwise.
public int indexOf(Object elem)
indexOf in interface List<E>
indexOf in class AbstractList<E>
elem - an object.
Object.equals(Object)
public int lastIndexOf(Object elem)
lastIndexOf in interface List<E>
lastIndexOf in class AbstractList<E>
elem - the desired element.
public Object clone()
clone in class Object
Cloneable
public Object[] toArray()
toArray in interface Collection<E>
toArray in interface List<E>
toArray in class AbstractCollection<E>
Arrays.asList(Object[])
public <T> T[] toArray(T[] a)
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.
toArray in interface Collection<E>
toArray in interface List<E>
toArray in class AbstractCollection<E>
a - 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.
ArrayStoreException - if the runtime type of a is not a supertype of the runtime type of every element in this list.
public E get(int index)
get in interface List<E>
get in class AbstractList<E>
index - index of element to return.
IndexOutOfBoundsException - if index is out of range (index < 0 || index >= size()).
public E set(int index,
E element)
set in interface List<E>
set in class AbstractList<E>
index - index of element to replace.
element - element to be stored at the specified position.
IndexOutOfBoundsException - if index out of range (index < 0 || index >= size()).
public boolean add(E o)
add in interface Collection<E>
add in interface List<E>
add in class AbstractList<E>
o - element to be appended to this list.
public void add(int index,
E element)
add in interface List<E>
add in class AbstractList<E>
index - index at which the specified element is to be inserted.
element - element to be inserted.
IndexOutOfBoundsException - if index is out of range (index < 0 || index > size()).
public E remove(int index)
remove in interface List<E>
remove in class AbstractList<E>
index - the index of the element to removed.
IndexOutOfBoundsException - if index out of range (index < 0 || index >= size()).
public boolean remove(Object o)
remove in interface Collection<E>
remove in interface List<E>
remove in class AbstractCollection<E>
o - element to be removed from this list, if present.
public void clear()
clear in interface Collection<E>
clear in interface List<E>
clear in class AbstractList<E>
public boolean addAll(Collection<? extends E> c)
addAll in interface Collection<E>
addAll in interface List<E>
addAll in class AbstractCollection<E>
c - the elements to be inserted into this list.
NullPointerException - if the specified collection is null.
AbstractCollection.add(Object)
public boolean addAll(int index,
Collection<? extends E> c)
addAll in interface List<E>
addAll in class AbstractList<E>
index - index at which to insert first element from the specified collection.
c - elements to be inserted into this list.
IndexOutOfBoundsException - if index out of range (index < 0 || index > size()).
NullPointerException - if the specified Collection is null.
protected void removeRange(int fromIndex,
int toIndex)
removeRange in class AbstractList<E>
fromIndex - index of first element to be removed.
toIndex - index after last element to be removed.
Copyright © 2004, 2010 Oracle and/or its affiliates. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.
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