Class ArrayList<E>
- java.lang.Object
-
- java.util.AbstractCollection<E>
-
- java.util.AbstractList<E>
-
- java.util.ArrayList<E>
- Type Parameters:
-
E
- the type of elements in this list
- 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 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:
-
Collection
,List
,LinkedList
,Vector
, Serialized Form
Field Summary
Fields declared in class java.util.AbstractList
modCount
Constructor Summary
Constructor | Description |
---|---|
ArrayList() | Constructs 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 Type | Method | Description |
---|---|---|
void | add(int index,
E element) | Inserts the specified element at the specified position in this list. |
boolean | add(E e) | 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 | clear() | Removes all of the elements from this list. |
Object | clone() | Returns a shallow copy of this |
boolean | contains(Object o) | Returns |
void | ensureCapacity(int minCapacity) | Increases the capacity of this |
void | forEach(Consumer<? super E> action) | Performs the given action for each element of the |
E | get(int index) | Returns the element at the specified position in this list. |
int | indexOf(Object o) | 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() | Returns |
Iterator<E> | iterator() | Returns an iterator over the elements in this list in proper sequence. |
int | lastIndexOf(Object o) | Returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element. |
ListIterator<E> | listIterator() | Returns a list iterator over the elements in this list (in proper sequence). |
ListIterator<E> | listIterator(int index) | Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list. |
E | remove(int index) | Removes the element at the specified position in this list. |
boolean | remove(Object o) | 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. |
boolean | removeIf(Predicate<? super E> filter) | Removes all of the elements of this collection that satisfy the given predicate. |
protected void | removeRange(int fromIndex,
int toIndex) | Removes from this list all of the elements whose index is between |
boolean | retainAll(Collection<?> c) | Retains only the elements in this list that are contained in the specified collection. |
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. |
Spliterator<E> | spliterator() | Creates a late-binding and fail-fast |
List<E> | subList(int fromIndex,
int toIndex) | Returns a view of the portion of this list between the specified |
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 | trimToSize() | Trims the capacity of this |
Methods declared in class java.util.AbstractList
equals, hashCode
Methods declared in class java.util.AbstractCollection
containsAll, toString
Methods declared in class java.lang.Object
finalize, getClass, notify, notifyAll, wait, wait, wait
Methods declared in interface java.util.Collection
parallelStream, stream, toArray
Methods declared in interface java.util.List
containsAll, equals, hashCode, replaceAll, sort
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
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.
- 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.
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 interfaceCollection<E>
- Specified by:
-
size
in interfaceList<E>
- Returns:
- the number of elements in this list
isEmpty
public boolean isEmpty()
Returns true
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
public boolean contains(Object o)
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 Objects.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
public int indexOf(Object o)
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 i
such that Objects.equals(o, get(i))
, or -1 if there is no such index.
- Specified by:
-
indexOf
in interfaceList<E>
- Overrides:
-
indexOf
in classAbstractList<E>
- Parameters:
-
o
- element to search for - Returns:
- the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element
lastIndexOf
public int lastIndexOf(Object o)
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 Objects.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
public Object clone()
Returns a shallow copy of this ArrayList
instance. (The elements themselves are not copied.)
toArray
public Object[] 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:
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 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 list -
NullPointerException
- if the specified array is null
get
public E get(int index)
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()
)
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 interfaceList<E>
- Overrides:
-
set
in classAbstractList<E>
- Parameters:
-
index
- index of the element to replace -
element
- 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
public boolean add(E e)
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
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 interfaceList<E>
- Overrides:
-
add
in classAbstractList<E>
- Parameters:
-
index
- index at which the specified element is to be inserted -
element
- element to be inserted - Throws:
-
IndexOutOfBoundsException
- if the 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 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()
)
remove
public boolean remove(Object o)
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 index i
such that Objects.equals(o, get(i))
(if such an element exists). Returns true
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
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 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:
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 interfaceList<E>
- Overrides:
-
addAll
in classAbstractList<E>
- Parameters:
-
index
- index at which to insert the first element from the specified collection -
c
- 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 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 classAbstractList<E>
- Parameters:
-
fromIndex
- index of first element to be removed -
toIndex
- index after last element to be removed - Throws:
-
IndexOutOfBoundsException
- iffromIndex
ortoIndex
is out of range (fromIndex < 0 || toIndex > size() || toIndex < fromIndex
)
removeAll
public boolean removeAll(Collection<?> c)
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:
Collection.contains(Object)
retainAll
public boolean retainAll(Collection<?> c)
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:
Collection.contains(Object)
listIterator
public ListIterator<E> listIterator(int index)
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 to next
. An initial call to previous
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
public ListIterator<E> 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:
listIterator(int)
iterator
public Iterator<E> iterator()
Returns an iterator over the elements in this list in proper sequence.
The returned iterator is fail-fast.
- Specified by:
-
iterator
in interfaceCollection<E>
- Specified by:
-
iterator
in interfaceIterable<E>
- Specified by:
-
iterator
in interfaceList<E>
- Overrides:
-
iterator
in classAbstractList<E>
- Returns:
- an iterator over the elements in this list in proper sequence
subList
public List<E> subList(int fromIndex, int toIndex)
Returns a view of the portion of this list between the specified fromIndex
, inclusive, and toIndex
, exclusive. (If fromIndex
and toIndex
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 for
indexOf(Object)
and lastIndexOf(Object)
, and all of the algorithms in the Collections
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 subList -
toIndex
- 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
public void forEach(Consumer<? super E> action)
Description copied from interface: Iterable
Performs the given action for each element of the Iterable
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
public Spliterator<E> spliterator()
Creates a late-binding and fail-fast Spliterator
over the elements in this list.
The Spliterator
reports Spliterator.SIZED
, Spliterator.SUBSIZED
, and Spliterator.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
public boolean removeIf(Predicate<? super E> filter)
Description copied from interface: Collection
Removes all of the elements of this collection that satisfy the given predicate. 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