public class ArrayList extends AbstractList implements List, RandomAccess, Cloneable, Serializable
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 FormmodCount| Constructor and Description |
|---|
ArrayList()
Constructs an empty list with an initial capacity of ten.
|
ArrayList(Collection c)
Constructs a list containing the elements of the specified
collection, in the order they are returned by the collection's
iterator.
|
ArrayList(int initialCapacity)
Constructs an empty list with the specified initial capacity.
|
| Modifier and Type | Method and Description |
|---|---|
void |
add(int index,
Object element)
Inserts the specified element at the specified position in this
list.
|
boolean |
add(Object o)
Appends the specified element to the end of this list.
|
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.
|
boolean |
addAll(int index,
Collection c)
Inserts all of the elements in the specified Collection into this
list, starting at the specified position.
|
void |
clear()
Removes all of the elements from this list.
|
Object |
clone()
Returns a shallow copy of this ArrayList instance.
|
boolean |
contains(Object elem)
Returns true if this list contains the specified element.
|
void |
ensureCapacity(int minCapacity)
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.
|
Object |
get(int index)
Returns the element at the specified position in this list.
|
int |
indexOf(Object elem)
Searches for the first occurence of the given argument, testing
for equality using the equals method.
|
boolean |
isEmpty()
Tests if this list has no elements.
|
int |
lastIndexOf(Object elem)
Returns the index of the last occurrence of the specified object in
this list.
|
Object |
remove(int index)
Removes the element at the specified position in this list.
|
protected void |
removeRange(int fromIndex,
int toIndex)
Removes from this List all of the elements whose index is between
fromIndex, inclusive and toIndex, exclusive.
|
Object |
set(int index,
Object element)
Replaces the element at the specified position in this list with
the specified element.
|
int |
size()
Returns the number of elements in this list.
|
Object[] |
toArray()
Returns an array containing all of the elements in this list
in the correct order.
|
Object[] |
toArray(Object[] a)
Returns an array containing all of the elements in this list in the
correct order; the runtime type of the returned array is that of the
specified array.
|
void |
trimToSize()
Trims the capacity of this ArrayList instance to be the
list's current size.
|
equals, hashCode, iterator, listIterator, listIterator, subListcontainsAll, remove, removeAll, retainAll, toStringfinalize, getClass, notify, notifyAll, wait, wait, waitcontainsAll, equals, hashCode, iterator, listIterator, listIterator, remove, removeAll, retainAll, subListpublic ArrayList(int initialCapacity)
initialCapacity - the initial capacity of the list.IllegalArgumentException - if the specified initial capacity
is negativepublic ArrayList()
public ArrayList(Collection 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 Collectionsize in interface Listsize in class AbstractCollectionpublic boolean isEmpty()
isEmpty in interface CollectionisEmpty in interface ListisEmpty in class AbstractCollectionpublic boolean contains(Object elem)
contains in interface Collectioncontains in interface Listcontains in class AbstractCollectionelem - 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 ListindexOf in class AbstractListelem - an object.Object.equals(Object)public int lastIndexOf(Object elem)
lastIndexOf in interface ListlastIndexOf in class AbstractListelem - the desired element.public Object clone()
public Object[] toArray()
toArray in interface CollectiontoArray in interface ListtoArray in class AbstractCollectionArrays.asList(Object[])public Object[] toArray(Object[] 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 CollectiontoArray in interface ListtoArray in class AbstractCollectiona - 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 Object get(int index)
get in interface Listget in class AbstractListindex - index of element to return.IndexOutOfBoundsException - if index is out of range (index
< 0 || index >= size()).public Object set(int index, Object element)
set in interface Listset in class AbstractListindex - 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(Object o)
add in interface Collectionadd in interface Listadd in class AbstractListo - element to be appended to this list.public void add(int index,
Object element)
add in interface Listadd in class AbstractListindex - 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 Object remove(int index)
remove in interface Listremove in class AbstractListindex - the index of the element to removed.IndexOutOfBoundsException - if index out of range (index
< 0 || index >= size()).public void clear()
clear in interface Collectionclear in interface Listclear in class AbstractListpublic boolean addAll(Collection c)
addAll in interface CollectionaddAll in interface ListaddAll in class AbstractCollectionc - the elements to be inserted into this list.NullPointerException - if the specified collection is null.AbstractCollection.add(Object)public boolean addAll(int index,
Collection c)
addAll in interface ListaddAll in class AbstractListindex - 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 AbstractListfromIndex - index of first element to be removed.toIndex - index after last element to be removed.Copyright © 2012. All Rights Reserved.