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Overview Package Class Use Tree Deprecated Index Help
JavaTM 2 Platform
Standard Ed. 5.0 PREV CLASS NEXT CLASS FRAMES NO FRAMES All Classes All
Classes SUMMARY: NESTED | FIELD | CONSTR | METHOD
DETAIL: FIELD | CONSTR | METHOD
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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
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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
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Field Summary
Fields inherited from class java.util.AbstractList modCount
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.
<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. void trimToSize()
Trims the capacity of this ArrayList instance to be the list's current
size.
Methods inherited from class java.util.AbstractList equals, hashCode, iterator,
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, equals, hashCode,
iterator, listIterator, listIterator, removeAll, retainAll, subList
Constructor Detail
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
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ARRAYLIST
public ArrayList()
Constructs an empty list with an initial capacity of ten.
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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.
Method Detail
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.
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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.
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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.
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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.
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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.
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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)
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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.
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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
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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[])
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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.
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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()).
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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()).
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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).
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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()).
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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()).
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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.
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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>
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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)
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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.
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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.
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Overview Package Class Use Tree Deprecated Index Help
JavaTM 2 Platform
Standard Ed. 5.0 PREV CLASS NEXT CLASS FRAMES NO FRAMES All Classes All
Classes SUMMARY: NESTED | FIELD | CONSTR | METHOD
DETAIL: FIELD | CONSTR | METHOD
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