JavaTM 2 Platform Std. Ed. v1.5.0
java.util
Class ArrayList<E>
java.lang.Object
java.util.AbstractCollection<E>
java.util.AbstractList<E>
java.util.ArrayList<E>
- All Implemented Interfaces:
- Serializable, Cloneable, Iterable<E>, Collection<E>, List<E>, RandomAccess
- Direct Known Subclasses:
- AttributeList, RoleList, RoleUnresolvedList
public class ArrayList<E> - extends AbstractList<E>
- implements List<E>, RandomAccess, Cloneable, Serializable
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.
- Since:
- 1.2
- See Also:
Collection ,
List ,
LinkedList ,
Vector ,
Collections.synchronizedList(List) ,
Serialized Form
Constructor Summary |
ArrayList()
Constructs an empty list with an initial capacity of ten. |
ArrayList(Collection<? extends E> 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. |
Method Summary |
boolean |
add(E o)
Appends the specified element to the end of this list. |
void |
add(int index,
E element)
Inserts the specified element at the specified position in this
list. |
boolean |
addAll(Collection<? extends E> 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<? extends E> 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. |
E |
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. |
E |
remove(int index)
Removes the element at the specified position in this list. |
boolean |
remove(Object o)
Removes a single instance of the specified element from this
list, if it is present (optional operation). |
protected void |
removeRange(int fromIndex,
int toIndex)
Removes from this List all of the elements whose index is between
fromIndex, inclusive and toIndex, exclusive. |
E |
set(int index,
E 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. |
|
toArray(T[] 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. |
ArrayList
public ArrayList(int initialCapacity)
- Constructs an empty list with the specified initial capacity.
- Parameters:
initialCapacity - the initial capacity of the list.
- Throws:
IllegalArgumentException - if the specified initial capacity
is negative
ArrayList
public ArrayList()
- Constructs an empty list with an initial capacity of ten.
ArrayList
public ArrayList(Collection<? extends E> c)
- Constructs a list containing the elements of the specified
collection, in the order they are returned by the collection's
iterator. The ArrayList instance has an initial capacity of
110% the size of the specified collection.
- Parameters:
c - the collection whose elements are to be placed into this list.
- Throws:
NullPointerException - if the specified collection is null.
trimToSize
public void trimToSize()
- 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.
ensureCapacity
public 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.
- Parameters:
minCapacity - the desired minimum capacity.
size
public int size()
- Returns the number of elements in this list.
- 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 list.
isEmpty
public boolean isEmpty()
- Tests if this list has no elements.
- Specified by:
isEmpty in interface Collection<E> - Specified by:
isEmpty in interface List<E> - Overrides:
isEmpty in class AbstractCollection<E>
- Returns:
- true if this list has no elements;
false otherwise.
contains
public boolean contains(Object elem)
- Returns true if this list contains the specified element.
- Specified by:
contains in interface Collection<E> - Specified by:
contains in interface List<E> - Overrides:
contains in class AbstractCollection<E>
- Parameters:
elem - element whose presence in this List is to be tested.
- Returns:
true if the specified element is present;
false otherwise.
indexOf
public int indexOf(Object elem)
- Searches for the first occurence of the given argument, testing
for equality using the equals method.
- Specified by:
indexOf in interface List<E> - Overrides:
indexOf in class AbstractList<E>
- Parameters:
elem - an object.
- Returns:
- the index of the first occurrence of the argument in this
list; returns -1 if the object is not found.
- See Also:
Object.equals(Object)
lastIndexOf
public int lastIndexOf(Object elem)
- Returns the index of the last occurrence of the specified object in
this list.
- Specified by:
lastIndexOf in interface List<E> - Overrides:
lastIndexOf in class AbstractList<E>
- Parameters:
elem - the desired element.
- Returns:
- the index of the last occurrence of the specified object in
this list; returns -1 if the object is not found.
clone
public Object clone()
- Returns a shallow copy of this ArrayList instance. (The
elements themselves are not copied.)
- Overrides:
clone in class Object
- Returns:
- a clone of this ArrayList instance.
- See Also:
Cloneable
toArray
public Object[] toArray()
- Returns an array containing all of the elements in this list
in the correct order.
- Specified by:
toArray in interface Collection<E> - Specified by:
toArray in interface List<E> - Overrides:
toArray in class AbstractCollection<E>
- Returns:
- an array containing all of the elements in this list
in the correct order.
- See Also:
Arrays.asList(Object[])
toArray
public <T> T[] toArray(T[] 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. 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.
- Specified by:
toArray in interface Collection<E> - Specified by:
toArray in interface List<E> - Overrides:
toArray in class AbstractCollection<E>
- Parameters:
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.
- Returns:
- an array containing the elements of the list.
- Throws:
ArrayStoreException - if the runtime type of a is not a supertype
of the runtime type of every element in this list.
get
public E get(int index)
- Returns the element at the specified position in this list.
- Specified by:
get in interface List<E> - Specified by:
get in class AbstractList<E>
- Parameters:
index - index of element to return.
- Returns:
- the element at the specified position in this list.
- Throws:
IndexOutOfBoundsException - if index is out of range (index
< 0 || index >= size()).
set
public E set(int index,
E element)
- Replaces the element at the specified position in this list with
the specified element.
- Specified by:
set in interface List<E> - Overrides:
set in class AbstractList<E>
- Parameters:
index - index of element to replace.element - element to be stored at the specified position.
- Returns:
- the element previously at the specified position.
- Throws:
IndexOutOfBoundsException - if index out of range
(index < 0 || index >= size()).
add
public boolean add(E o)
- Appends the specified element to the end of this list.
- Specified by:
add in interface Collection<E> - Specified by:
add in interface List<E> - Overrides:
add in class AbstractList<E>
- Parameters:
o - element to be appended to this list.
- Returns:
- true (as per the general contract of Collection.add).
add
public void add(int index,
E element)
- 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).
- Specified by:
add in interface List<E> - Overrides:
add in class AbstractList<E>
- Parameters:
index - index at which the specified element is to be inserted.element - element to be inserted.
- Throws:
IndexOutOfBoundsException - if index is out of range
(index < 0 || index > size()).
remove
public E remove(int index)
- Removes the element at the specified position in this list.
Shifts any subsequent elements to the left (subtracts one from their
indices).
- Specified by:
remove in interface List<E> - Overrides:
remove in class AbstractList<E>
- Parameters:
index - the index of the element to removed.
- Returns:
- the element that was removed from the list.
- Throws:
IndexOutOfBoundsException - if index out of range (index
< 0 || index >= size()).
remove
public boolean remove(Object o)
- Removes a single instance of the specified element from this
list, if it is present (optional operation). More formally,
removes an element e such that (o==null ? e==null :
o.equals(e)), if the list contains one or more such
elements. Returns true if the list contained the
specified element (or equivalently, if the list changed as a
result of the call).
- Specified by:
remove in interface Collection<E> - Specified by:
remove in interface List<E> - Overrides:
remove in class AbstractCollection<E>
- Parameters:
o - element to be removed from this list, if present.
- Returns:
- true if the list contained the specified element.
clear
public void clear()
- Removes all of the elements from this list. The list will
be empty after this call returns.
- Specified by:
clear in interface Collection<E> - Specified by:
clear in interface List<E> - Overrides:
clear in class AbstractList<E>
addAll
public boolean addAll(Collection<? extends E> 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. 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.)
- Specified by:
addAll in interface Collection<E> - Specified by:
addAll in interface List<E> - Overrides:
addAll in class AbstractCollection<E>
- Parameters:
c - the elements to be inserted into this list.
- Returns:
- true if this list changed as a result of the call.
- Throws:
NullPointerException - if the specified collection is null.- See Also:
AbstractCollection.add(Object)
addAll
public boolean addAll(int index,
Collection<? extends E> c)
- 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.
- Specified by:
addAll in interface List<E> - Overrides:
addAll in class AbstractList<E>
- Parameters:
index - index at which to insert first element
from the specified collection.c - elements to be inserted into this list.
- Returns:
- true if this list changed as a result of the call.
- Throws:
IndexOutOfBoundsException - if index out of range (index
< 0 || index > size()).
NullPointerException - if the specified Collection is null.
removeRange
protected void removeRange(int fromIndex,
int toIndex)
- 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.)
- Overrides:
removeRange in class AbstractList<E>
- Parameters:
fromIndex - index of first element to be removed.toIndex - index after last element to be removed.
Copyright 2003 Sun Microsystems, Inc. All rights reserved
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