Class ArrayList<E>
- Type Parameters:
E
- the type of elements in this list
- All Implemented Interfaces:
Serializable
,Cloneable
,Iterable<E>
,Collection<E>
,List<E>
,RandomAccess
,SequencedCollection<E>
- Direct Known Subclasses:
AttributeList
,RoleList
,RoleUnresolvedList
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
,
getFirst
, getLast
, removeLast
, iterator
,
listIterator
, and reversed
operations run in constant time.
The add
, and addLast
operations 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 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
. 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:
-
Field Summary
Fields inherited from class java.util.AbstractList
modCount
-
Constructor Summary
ConstructorDescriptionConstructs an empty list with an initial capacity of ten.ArrayList
(int initialCapacity) Constructs an empty list with the specified initial capacity.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. -
Method Summary
Modifier and TypeMethodDescriptionvoid
Inserts the specified element at the specified position in this list.boolean
Appends the specified element to the end of this list.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.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.void
Adds an element as the first element of this collection (optional operation).void
Adds an element as the last element of this collection (optional operation).void
clear()
Removes all of the elements from this list.clone()
Returns a shallow copy of thisArrayList
instance.boolean
Returnstrue
if this list contains the specified element.void
ensureCapacity
(int minCapacity) Increases the capacity of thisArrayList
instance, if necessary, to ensure that it can hold at least the number of elements specified by the minimum capacity argument.boolean
Compares the specified object with this list for equality.void
Performs the given action for each element of theIterable
until all elements have been processed or the action throws an exception.get
(int index) Returns the element at the specified position in this list.getFirst()
Gets the first element of this collection.getLast()
Gets the last element of this collection.int
hashCode()
Returns the hash code value for this list.int
Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element.boolean
isEmpty()
Returnstrue
if this list contains no elements.iterator()
Returns an iterator over the elements in this list in proper sequence.int
Returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element.Returns a list iterator over the elements in this list (in proper sequence).listIterator
(int index) Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list.remove
(int index) Removes the element at the specified position in this list.boolean
Removes the first occurrence of the specified element from this list, if it is present.boolean
removeAll
(Collection<?> c) Removes from this list all of its elements that are contained in the specified collection.Removes and returns the first element of this collection (optional operation).boolean
Removes all of the elements of this collection that satisfy the given predicate (optional operation).Removes and returns the last element of this collection (optional operation).protected void
removeRange
(int fromIndex, int toIndex) Removes from this list all of the elements whose index is betweenfromIndex
, inclusive, andtoIndex
, exclusive.void
replaceAll
(UnaryOperator<E> operator) Replaces each element of this list with the result of applying the operator to that element (optional operation).boolean
retainAll
(Collection<?> c) Retains only the elements in this list that are contained in the specified collection.Replaces the element at the specified position in this list with the specified element.int
size()
Returns the number of elements in this list.void
sort
(Comparator<? super E> c) Sorts this list according to the order induced by the specifiedComparator
(optional operation).Creates a late-binding and fail-fastSpliterator
over the elements in this list.subList
(int fromIndex, int toIndex) Returns a view of the portion of this list between the specifiedfromIndex
, inclusive, andtoIndex
, exclusive.Object[]
toArray()
Returns an array containing all of the elements in this list in proper sequence (from first to last element).<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 runtime type of the returned array is that of the specified array.void
Trims the capacity of thisArrayList
instance to be the list's current size.Methods inherited from class java.util.AbstractCollection
containsAll, toString
Methods inherited from class java.lang.Object
finalize, getClass, notify, notifyAll, wait, wait, wait
Methods inherited from interface java.util.Collection
parallelStream, stream, toArray
Methods inherited from interface java.util.List
containsAll, reversed
-
Constructor Details
-
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
Constructs a list containing the elements of the specified collection, in the order they are returned by the collection's iterator.- Parameters:
c
- the collection whose elements are to be placed into this list- Throws:
NullPointerException
- if the specified collection is null
-
-
Method Details
-
trimToSize
public void trimToSize()Trims the capacity of thisArrayList
instance to be the list's current size. An application can use this operation to minimize the storage of anArrayList
instance. -
ensureCapacity
public void ensureCapacity(int minCapacity) Increases the capacity of thisArrayList
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 interfaceCollection<E>
- Specified by:
size
in interfaceList<E>
- Specified by:
size
in classAbstractCollection<E>
- Returns:
- the number of elements in this list
-
isEmpty
public boolean isEmpty()Returnstrue
if this list contains no elements.- Specified by:
isEmpty
in interfaceCollection<E>
- Specified by:
isEmpty
in interfaceList<E>
- Overrides:
isEmpty
in classAbstractCollection<E>
- Returns:
true
if this list contains no elements
-
contains
Returnstrue
if this list contains the specified element. More formally, returnstrue
if and only if this list contains at least one elemente
such thatObjects.equals(o, e)
.- Specified by:
contains
in interfaceCollection<E>
- Specified by:
contains
in interfaceList<E>
- Overrides:
contains
in classAbstractCollection<E>
- Parameters:
o
- element whose presence in this list is to be tested- Returns:
true
if this list contains the specified element
-
indexOf
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 indexi
such thatObjects.equals(o, get(i))
, or -1 if there is no such index. -
lastIndexOf
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 indexi
such thatObjects.equals(o, get(i))
, or -1 if there is no such index.- Specified by:
lastIndexOf
in interfaceList<E>
- Overrides:
lastIndexOf
in classAbstractList<E>
- Parameters:
o
- element to search for- Returns:
- the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element
-
clone
-
toArray
Returns an array containing all of the elements in this list in proper sequence (from first to last element).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 interfaceCollection<E>
- Specified by:
toArray
in interfaceList<E>
- Overrides:
toArray
in classAbstractCollection<E>
- Returns:
- an array containing all of the elements in this list in proper sequence
- See Also:
-
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 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 interfaceCollection<E>
- Specified by:
toArray
in interfaceList<E>
- Overrides:
toArray
in classAbstractCollection<E>
- Type Parameters:
T
- the component type of the array to contain the collection- 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 the specified array is not a supertype of the runtime type of every element in this listNullPointerException
- if the specified array is null
-
get
Returns the element at the specified position in this list.- Specified by:
get
in interfaceList<E>
- Specified by:
get
in classAbstractList<E>
- Parameters:
index
- index of the element to return- Returns:
- the element at the specified position in this list
- Throws:
IndexOutOfBoundsException
- if the index is out of range (index < 0 || index >= size()
)
-
getFirst
Gets the first element of this collection.- Specified by:
getFirst
in interfaceList<E>
- Specified by:
getFirst
in interfaceSequencedCollection<E>
- Returns:
- the retrieved element
- Throws:
NoSuchElementException
- if this collection is empty- Since:
- 21
-
getLast
Gets the last element of this collection.- Specified by:
getLast
in interfaceList<E>
- Specified by:
getLast
in interfaceSequencedCollection<E>
- Returns:
- the retrieved element
- Throws:
NoSuchElementException
- if this collection is empty- Since:
- 21
-
set
Replaces the element at the specified position in this list with the specified element.- Specified by:
set
in interfaceList<E>
- Overrides:
set
in classAbstractList<E>
- Parameters:
index
- index of the element to replaceelement
- element to be stored at the specified position- Returns:
- the element previously at the specified position
- Throws:
IndexOutOfBoundsException
- if the index is out of range (index < 0 || index >= size()
)
-
add
Appends the specified element to the end of this list.- Specified by:
add
in interfaceCollection<E>
- Specified by:
add
in interfaceList<E>
- Overrides:
add
in classAbstractList<E>
- Parameters:
e
- element to be appended to this list- Returns:
true
(as specified byCollection.add(E)
)
-
add
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 interfaceList<E>
- Overrides:
add
in classAbstractList<E>
- Parameters:
index
- index at which the specified element is to be insertedelement
- element to be inserted- Throws:
IndexOutOfBoundsException
- if the index is out of range (index < 0 || index > size()
)
-
addFirst
Adds an element as the first element of this collection (optional operation). After this operation completes normally, the given element will be a member of this collection, and it will be the first element in encounter order. -
addLast
Adds an element as the last element of this collection (optional operation). After this operation completes normally, the given element will be a member of this collection, and it will be the last element in encounter order. -
remove
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 interfaceList<E>
- Overrides:
remove
in classAbstractList<E>
- Parameters:
index
- the index of the element to be removed- Returns:
- the element that was removed from the list
- Throws:
IndexOutOfBoundsException
- if the index is out of range (index < 0 || index >= size()
)
-
removeFirst
Removes and returns the first element of this collection (optional operation).- Specified by:
removeFirst
in interfaceList<E>
- Specified by:
removeFirst
in interfaceSequencedCollection<E>
- Returns:
- the removed element
- Throws:
NoSuchElementException
- if this collection is empty- Since:
- 21
-
removeLast
Removes and returns the last element of this collection (optional operation).- Specified by:
removeLast
in interfaceList<E>
- Specified by:
removeLast
in interfaceSequencedCollection<E>
- Returns:
- the removed element
- Throws:
NoSuchElementException
- if this collection is empty- Since:
- 21
-
equals
Compares the specified object with this list for equality. Returnstrue
if and only if the specified object is also a list, both lists have the same size, and all corresponding pairs of elements in the two lists are equal. (Two elementse1
ande2
are equal if(e1==null ? e2==null : e1.equals(e2))
.) In other words, two lists are defined to be equal if they contain the same elements in the same order.- Specified by:
equals
in interfaceCollection<E>
- Specified by:
equals
in interfaceList<E>
- Overrides:
equals
in classAbstractList<E>
- Parameters:
o
- the object to be compared for equality with this list- Returns:
true
if the specified object is equal to this list- See Also:
-
hashCode
public int hashCode()Returns the hash code value for this list.- Specified by:
hashCode
in interfaceCollection<E>
- Specified by:
hashCode
in interfaceList<E>
- Overrides:
hashCode
in classAbstractList<E>
- Returns:
- the hash code value for this list
- See Also:
-
remove
Removes the first occurrence of the specified element from this list, if it is present. If the list does not contain the element, it is unchanged. More formally, removes the element with the lowest indexi
such thatObjects.equals(o, get(i))
(if such an element exists). Returnstrue
if this list contained the specified element (or equivalently, if this list changed as a result of the call).- Specified by:
remove
in interfaceCollection<E>
- Specified by:
remove
in interfaceList<E>
- Overrides:
remove
in classAbstractCollection<E>
- Parameters:
o
- element to be removed from this list, if present- Returns:
true
if this 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 interfaceCollection<E>
- Specified by:
clear
in interfaceList<E>
- Overrides:
clear
in classAbstractList<E>
-
addAll
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 interfaceCollection<E>
- Specified by:
addAll
in interfaceList<E>
- Overrides:
addAll
in classAbstractCollection<E>
- Parameters:
c
- collection containing elements to be added to this list- Returns:
true
if this list changed as a result of the call- Throws:
NullPointerException
- if the specified collection is null- See Also:
-
addAll
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 interfaceList<E>
- Overrides:
addAll
in classAbstractList<E>
- Parameters:
index
- index at which to insert the first element from the specified collectionc
- collection containing elements to be added to this list- Returns:
true
if this list changed as a result of the call- Throws:
IndexOutOfBoundsException
- if the index is 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 betweenfromIndex
, inclusive, andtoIndex
, exclusive. Shifts any succeeding elements to the left (reduces their index). This call shortens the list by(toIndex - fromIndex)
elements. (IftoIndex==fromIndex
, this operation has no effect.)- Overrides:
removeRange
in classAbstractList<E>
- Parameters:
fromIndex
- index of first element to be removedtoIndex
- index after last element to be removed- Throws:
IndexOutOfBoundsException
- iffromIndex
ortoIndex
is out of range (fromIndex < 0 || toIndex > size() || toIndex < fromIndex
)
-
removeAll
Removes from this list all of its elements that are contained in the specified collection.- Specified by:
removeAll
in interfaceCollection<E>
- Specified by:
removeAll
in interfaceList<E>
- Overrides:
removeAll
in classAbstractCollection<E>
- Parameters:
c
- collection containing elements to be removed from this list- Returns:
true
if this list changed as a result of the call- Throws:
ClassCastException
- if the class of an element of this list is incompatible with the specified collection (optional)NullPointerException
- if this list contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is null- See Also:
-
retainAll
Retains only the elements in this list that are contained in the specified collection. In other words, removes from this list all of its elements that are not contained in the specified collection.- Specified by:
retainAll
in interfaceCollection<E>
- Specified by:
retainAll
in interfaceList<E>
- Overrides:
retainAll
in classAbstractCollection<E>
- Parameters:
c
- collection containing elements to be retained in this list- Returns:
true
if this list changed as a result of the call- Throws:
ClassCastException
- if the class of an element of this list is incompatible with the specified collection (optional)NullPointerException
- if this list contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is null- See Also:
-
listIterator
Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list. The specified index indicates the first element that would be returned by an initial call tonext
. An initial call toprevious
would return the element with the specified index minus one.The returned list iterator is fail-fast.
- Specified by:
listIterator
in interfaceList<E>
- Overrides:
listIterator
in classAbstractList<E>
- Parameters:
index
- index of the first element to be returned from the list iterator (by a call tonext
)- Returns:
- a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list
- Throws:
IndexOutOfBoundsException
- if the index is out of range (index < 0 || index > size()
)
-
listIterator
Returns a list iterator over the elements in this list (in proper sequence).The returned list iterator is fail-fast.
- Specified by:
listIterator
in interfaceList<E>
- Overrides:
listIterator
in classAbstractList<E>
- Returns:
- a list iterator over the elements in this list (in proper sequence)
- See Also:
-
iterator
Returns an iterator over the elements in this list in proper sequence.The returned iterator is fail-fast.
-
subList
Returns a view of the portion of this list between the specifiedfromIndex
, inclusive, andtoIndex
, exclusive. (IffromIndex
andtoIndex
are equal, the returned list is empty.) The returned list is backed by this list, so non-structural changes in the returned list are reflected in this list, and vice-versa. The returned list supports all of the optional list operations.This method eliminates the need for explicit range operations (of the sort that commonly exist for arrays). Any operation that expects a list can be used as a range operation by passing a subList view instead of a whole list. For example, the following idiom removes a range of elements from a list:
list.subList(from, to).clear();
Similar idioms may be constructed forindexOf(Object)
andlastIndexOf(Object)
, and all of the algorithms in theCollections
class can be applied to a subList.The semantics of the list returned by this method become undefined if the backing list (i.e., this list) is structurally modified in any way other than via the returned list. (Structural modifications are those that change the size of this list, or otherwise perturb it in such a fashion that iterations in progress may yield incorrect results.)
- Specified by:
subList
in interfaceList<E>
- Overrides:
subList
in classAbstractList<E>
- Parameters:
fromIndex
- low endpoint (inclusive) of the subListtoIndex
- high endpoint (exclusive) of the subList- Returns:
- a view of the specified range within this list
- Throws:
IndexOutOfBoundsException
- if an endpoint index value is out of range(fromIndex < 0 || toIndex > size)
IllegalArgumentException
- if the endpoint indices are out of order(fromIndex > toIndex)
-
forEach
Description copied from interface:Iterable
Performs the given action for each element of theIterable
until all elements have been processed or the action throws an exception. Actions are performed in the order of iteration, if that order is specified. Exceptions thrown by the action are relayed to the caller.The behavior of this method is unspecified if the action performs side-effects that modify the underlying source of elements, unless an overriding class has specified a concurrent modification policy.
- Specified by:
forEach
in interfaceIterable<E>
- Parameters:
action
- The action to be performed for each element- Throws:
NullPointerException
- if the specified action is null
-
spliterator
Creates a late-binding and fail-fastSpliterator
over the elements in this list.The
Spliterator
reportsSpliterator.SIZED
,Spliterator.SUBSIZED
, andSpliterator.ORDERED
. Overriding implementations should document the reporting of additional characteristic values.- Specified by:
spliterator
in interfaceCollection<E>
- Specified by:
spliterator
in interfaceIterable<E>
- Specified by:
spliterator
in interfaceList<E>
- Returns:
- a
Spliterator
over the elements in this list - Since:
- 1.8
-
removeIf
Description copied from interface:Collection
Removes all of the elements of this collection that satisfy the given predicate (optional operation). Errors or runtime exceptions thrown during iteration or by the predicate are relayed to the caller.- Specified by:
removeIf
in interfaceCollection<E>
- Parameters:
filter
- a predicate which returnstrue
for elements to be removed- Returns:
true
if any elements were removed- Throws:
NullPointerException
- if the specified filter is null
-
replaceAll
Description copied from interface:List
Replaces each element of this list with the result of applying the operator to that element (optional operation). Errors or runtime exceptions thrown by the operator are relayed to the caller.- Specified by:
replaceAll
in interfaceList<E>
- Parameters:
operator
- the operator to apply to each element
-
sort
Description copied from interface:List
Sorts this list according to the order induced by the specifiedComparator
(optional operation). The sort is stable: this method must not reorder equal elements.All elements in this list must be mutually comparable using the specified comparator (that is,
c.compare(e1, e2)
must not throw aClassCastException
for any elementse1
ande2
in the list).If the specified comparator is
null
then all elements in this list must implement theComparable
interface and the elements' natural ordering should be used.This list must be modifiable, but need not be resizable.
- Specified by:
sort
in interfaceList<E>
- Parameters:
c
- theComparator
used to compare list elements. Anull
value indicates that the elements' natural ordering should be used
-