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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
-
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
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
the
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
.
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
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
Appends all of the elements in the specified
collection
Collection
to the end of this list, in the order that they are returned by the specified
collection's
Collection's
Iterator. |
boolean |
addAll
(int index,
Collection
<? extends
E
Inserts all of the elements in the specified
collection
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
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
Returns
Searches for
the
index of the
first
occurrence
occurence
of the
specified element in this list, or -1 if this list does not contain
given argument, testing for equality using
the
element.
equals
method.
|
boolean |
isEmpty
()
Returns
true
Tests
if this list
contains
has
no elements. |
int |
lastIndexOf
(
Object
Returns the index of the last occurrence of the specified
element
object
in this
list, or -1 if this list does not contain the element.
list.
|
E
|
remove
(int index)
Removes the element at the specified position in this list. |
boolean |
remove
(
Object
Removes
the first occurrence
a single instance
of the specified element from this list, if it is
present.
present (optional operation).
|
protected void |
removeRange
(int fromIndex, int toIndex)
Removes from this
list
List
all of the elements whose index is between
fromIndex
, inclusive,
fromIndex, inclusive
and
toIndex
,
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
proper sequence (from first to last element).
the correct order.
|
|
toArray
(T[] a)
Returns an array containing all of the elements in this list in
proper sequence (from first to last element);
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
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
list.
-
Throws:
-
NullPointerException
- if the specified collection is
null
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
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
list.
isEmpty
public boolean isEmpty()
-
Returns
true
Tests
if this list
contains
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
contains
has
no
elements
elements;
false
otherwise.
contains
public boolean contains(Object o) elem)
-
Returns
true
if this list contains the specified element.
More formally, returns
true
if and only if this list contains at least one element
e
such that
(o==null ? e==null : o.equals(e))
.
-
-
Specified by:
-
contains
in interface
Collection
<
E
>
-
Specified by:
-
contains
in interface
List
<
E
>
-
Overrides:
-
contains
in class
AbstractCollection
<
E
>
-
-
Parameters:
-
o
elem
- element whose presence in this
list
List
is to be
tested
tested.
-
Returns:
-
true
if
this list contains
the specified element
is present; false otherwise.
indexOf
public int indexOf(Object o) elem)
-
Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element. More formally, returns the lowest index
Searches for the first occurence of the given argument, testing for equality using the
i
equals
such that
(o==null ? get(i)==null : o.equals(get(i)))
, or -1 if there is no such index.
method.
-
-
Specified by:
-
indexOf
in interface
List
<
E
>
-
Overrides:
-
indexOf
in class
AbstractList
<
E
>
-
-
Parameters:
-
o - element to search for
elem - an object.
-
Returns:
-
the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element
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 o) elem)
-
Returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element. More formally, returns the highest index
i
such that
(o==null ? get(i)==null : o.equals(get(i)))
, or -1 if there is no such index.
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:
-
o - element to search for
elem - the desired element.
-
Returns:
-
the index of the last occurrence of the specified
element
object
in this
list, or
list; returns
-1 if
this list does
the object is
not
contain the element
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
instance.
-
See Also:
-
Cloneable
toArray
public Object[] toArray()
-
Returns an array containing all of the elements in this list in
proper sequence (from first to last element).
the correct order.
The returned array will be "safe" in that no references to it are maintained by this list. (In other words, this method must allocate a new array). The caller is thus free to modify the returned array.
This method acts as bridge between array-based and collection-based APIs.
-
-
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
proper sequence
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
proper sequence (from first to last element);
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
This
is useful in determining the length of the list
only
if the caller knows that the list does not contain any
null
elements.)
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
list.
-
Throws:
-
ArrayStoreException
- if the runtime type of
the specified array
a
is not a supertype of the runtime type of every element in this
list
-
NullPointerException
- if the specified array is null
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
the
element to
return
return.
-
Returns:
-
the element at the specified position in this
list
list.
-
Throws:
-
IndexOutOfBoundsException
- if
the
index is out of range
(
index
(index
< 0 || index >=
size()
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
the
element to
replace
replace.
-
element - element to be stored at the specified
position
position.
-
Returns:
-
the element previously at the specified
position
position.
-
Throws:
-
IndexOutOfBoundsException
- if
the
index
is
out of range
(
index
(index
< 0 || index >=
size()
size())
)
.
add
public boolean add(E 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:
-
e
o
- element to be appended to this
list
list.
-
Returns:
-
true
(as specified by
Collection.add(E)
)
(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
inserted.
-
element - element to be
inserted
inserted.
-
Throws:
-
IndexOutOfBoundsException
- if
the
index is out of range
(
index
(index
< 0 || index >
size()
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
be removed
removed.
-
Returns:
-
the element that was removed from the
list
list.
-
Throws:
-
IndexOutOfBoundsException
- if
the
index
is
out of range
(
index
(index
< 0 || index >=
size()
size())
)
.
remove
public boolean remove(Object o)
-
Removes
the first occurrence
a single instance
of the specified element from this list, if it is
present. If the list does not contain the element, it is unchanged.
present (optional operation).
More formally, removes
the
an
element
with the lowest index
i
e
such that
(o==null ? get(i)==null : o.equals(get(i)))
(o==null ? e==null : o.equals(e))
(if such an element exists).
, if the list contains one or more such elements.
Returns
true
if
this
the
list contained the specified element (or equivalently, if
this
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
present.
-
Returns:
-
true
if
this
the
list contained the specified
element
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
Collection
to the end of this list, in the order that they are returned by the specified
collection's
Collection's
Iterator. The behavior of this operation is undefined if the specified
collection
Collection
is modified while the operation is in progress. (This implies that the behavior of this call is undefined if the specified
collection
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 -
collection containing
the
elements to be
added to
inserted into
this
list
list.
-
Returns:
-
true
if this list changed as a result of the
call
call.
-
Throws:
-
NullPointerException
- if the specified collection is
null
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
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
Collection's
iterator.
-
-
Specified by:
-
addAll
in interface
List
<
E
>
-
Overrides:
-
addAll
in class
AbstractList
<
E
>
-
-
Parameters:
-
index - index at which to insert
the
first element from the specified
collection
collection.
-
c -
collection containing
elements to be
added to
inserted into
this
list
list.
-
Returns:
-
true
if this list changed as a result of the
call
call.
-
Throws:
-
IndexOutOfBoundsException
- if
the
index
is
out of range
(
index
(index
< 0 || index >
size()
size())
)
.
-
NullPointerException
- if the specified
collection
Collection
is
null
null.
removeRange
protected void removeRange(int fromIndex,
int toIndex)
-
Removes from this
list
List
all of the elements whose index is between
fromIndex
, inclusive,
fromIndex, inclusive
and
toIndex
,
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
removed.
-
toIndex - index after last element to be removed
-
Throws:
-
IndexOutOfBoundsException
- if fromIndex or toIndex out of range (fromIndex < 0 || fromIndex >= size() || toIndex > size() || toIndex < fromIndex)
toIndex - index after last element to be removed.