E
- the type of elements in this listCollection<E>
, Iterable<E>
, SequencedCollection<E>
AbstractList
, AbstractSequentialList
, ArrayList
, AttributeList
, CopyOnWriteArrayList
, LinkedList
, RoleList
, RoleUnresolvedList
, Stack
, Vector
public interface List<E> extends SequencedCollection<E>
Unlike sets, lists typically allow duplicate elements. More formally, lists typically allow pairs of elements e1
and e2
such that e1.equals(e2)
, and they typically allow multiple null elements if they allow null elements at all. It is not inconceivable that someone might wish to implement a list that prohibits duplicates, by throwing runtime exceptions when the user attempts to insert them, but we expect this usage to be rare.
The List
interface places additional stipulations, beyond those specified in the Collection
interface, on the contracts of the iterator
, add
, remove
, equals
, and hashCode
methods. Declarations for other inherited methods are also included here for convenience.
The List
interface provides four methods for positional (indexed) access to list elements. Lists (like Java arrays) are zero based. Note that these operations may execute in time proportional to the index value for some implementations (the LinkedList
class, for example). Thus, iterating over the elements in a list is typically preferable to indexing through it if the caller does not know the implementation.
The List
interface provides a special iterator, called a ListIterator
, that allows element insertion and replacement, and bidirectional access in addition to the normal operations that the Iterator
interface provides. A method is provided to obtain a list iterator that starts at a specified position in the list.
The List
interface provides two methods to search for a specified object. From a performance standpoint, these methods should be used with caution. In many implementations they will perform costly linear searches.
The List
interface provides two methods to efficiently insert and remove multiple elements at an arbitrary point in the list.
Note: While it is permissible for lists to contain themselves as elements, extreme caution is advised: the equals
and hashCode
methods are no longer well defined on such a list.
Some list implementations have restrictions on the elements that they may contain. For example, some implementations prohibit null elements, and some have restrictions on the types of their elements. Attempting to add an ineligible element throws an unchecked exception, typically NullPointerException
or ClassCastException
. Attempting to query the presence of an ineligible element may throw an exception, or it may simply return false; some implementations will exhibit the former behavior and some will exhibit the latter. More generally, attempting an operation on an ineligible element whose completion would not result in the insertion of an ineligible element into the list may throw an exception or it may succeed, at the option of the implementation. Such exceptions are marked as "optional" in the specification for this interface.
The List.of
and List.copyOf
static factory methods provide a convenient way to create unmodifiable lists. The List
instances created by these methods have the following characteristics:
UnsupportedOperationException
to be thrown. However, if the contained elements are themselves mutable, this may cause the List's contents to appear to change. null
elements. Attempts to create them with null
elements result in NullPointerException
. subList
views implement the RandomAccess
interface. This interface is a member of the Java Collections Framework.
Modifier and Type | Method | Description |
---|---|---|
void |
add |
Inserts the specified element at the specified position in this list (optional operation). |
boolean |
add |
Appends the specified element to the end of this list (optional operation). |
boolean |
addAll |
Inserts all of the elements in the specified collection into this list at the specified position (optional operation). |
boolean |
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 (optional operation). |
default void |
addFirst |
Adds an element as the first element of this collection (optional operation). |
default void |
addLast |
Adds an element as the last element of this collection (optional operation). |
void |
clear() |
Removes all of the elements from this list (optional operation). |
boolean |
contains |
Returns true if this list contains the specified element. |
boolean |
containsAll |
Returns true if this list contains all of the elements of the specified collection. |
static <E> List |
copyOf |
Returns an unmodifiable List containing the elements of the given Collection, in its iteration order. |
boolean |
equals |
Compares the specified object with this list for equality. |
E |
get |
Returns the element at the specified position in this list. |
default E |
getFirst() |
Gets the first element of this collection. |
default E |
getLast() |
Gets the last element of this collection. |
int |
hashCode() |
Returns the hash code value for this list. |
int |
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. |
boolean |
isEmpty() |
Returns true if this list contains no elements. |
Iterator |
iterator() |
Returns an iterator over the elements in this list in proper sequence. |
int |
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. |
ListIterator |
listIterator() |
Returns a list iterator over the elements in this list (in proper sequence). |
ListIterator |
listIterator |
Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list. |
static <E> List |
of() |
Returns an unmodifiable list containing zero elements. |
static <E> List |
of |
Returns an unmodifiable list containing one element. |
static <E> List |
of |
Returns an unmodifiable list containing an arbitrary number of elements. |
static <E> List |
of |
Returns an unmodifiable list containing two elements. |
static <E> List |
of |
Returns an unmodifiable list containing three elements. |
static <E> List |
of |
Returns an unmodifiable list containing four elements. |
static <E> List |
of |
Returns an unmodifiable list containing five elements. |
static <E> List |
of |
Returns an unmodifiable list containing six elements. |
static <E> List |
of |
Returns an unmodifiable list containing seven elements. |
static <E> List |
of |
Returns an unmodifiable list containing eight elements. |
static <E> List |
of |
Returns an unmodifiable list containing nine elements. |
static <E> List |
of |
Returns an unmodifiable list containing ten elements. |
E |
remove |
Removes the element at the specified position in this list (optional operation). |
boolean |
remove |
Removes the first occurrence of the specified element from this list, if it is present (optional operation). |
boolean |
removeAll |
Removes from this list all of its elements that are contained in the specified collection (optional operation). |
default E |
removeFirst() |
Removes and returns the first element of this collection (optional operation). |
default E |
removeLast() |
Removes and returns the last element of this collection (optional operation). |
default void |
replaceAll |
Replaces each element of this list with the result of applying the operator to that element. |
boolean |
retainAll |
Retains only the elements in this list that are contained in the specified collection (optional operation). |
default List |
reversed() |
Returns a reverse-ordered view of this collection. |
E |
set |
Replaces the element at the specified position in this list with the specified element (optional operation). |
int |
size() |
Returns the number of elements in this list. |
default void |
sort |
Sorts this list according to the order induced by the specified Comparator . |
default Spliterator |
spliterator() |
Creates a Spliterator over the elements in this list. |
List |
subList |
Returns a view of the portion of this list between the specified fromIndex , inclusive, and toIndex , 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 |
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. |
parallelStream, removeIf, stream, toArray
int size()
Integer.MAX_VALUE
elements, returns Integer.MAX_VALUE
.size
in interface Collection<E>
boolean isEmpty()
true
if this list contains no elements.isEmpty
in interface Collection<E>
true
if this list contains no elementsboolean contains(Object o)
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)
.contains
in interface Collection<E>
o
- element whose presence in this list is to be testedtrue
if this list contains the specified elementClassCastException
- if the type of the specified element is incompatible with this list (optional)NullPointerException
- if the specified element is null and this list does not permit null elements (optional)Iterator<E> iterator()
Object[] toArray()
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 even if this list is backed by an array). The caller is thus free to modify the returned array.
This method acts as bridge between array-based and collection-based APIs.
toArray
in interface Collection<E>
<T> T[] toArray(T[] a)
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 list 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.)
Like the toArray()
method, this method acts as bridge between array-based and collection-based APIs. Further, this method allows precise control over the runtime type of the output array, and may, under certain circumstances, be used to save allocation costs.
Suppose x
is a list known to contain only strings. The following code can be used to dump the list into a newly allocated array of String
:
String[] y = x.toArray(new String[0]);
Note that toArray(new Object[0])
is identical in function to toArray()
.toArray
in interface Collection<E>
T
- the component type of the array to contain the collectiona
- the array into which the elements of this list are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.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 nullboolean add(E e)
Lists that support this operation may place limitations on what elements may be added to this list. In particular, some lists will refuse to add null elements, and others will impose restrictions on the type of elements that may be added. List classes should clearly specify in their documentation any restrictions on what elements may be added.
add
in interface Collection<E>
e
- element to be appended to this listtrue
(as specified by Collection.add(E)
)UnsupportedOperationException
- if the add
operation is not supported by this listClassCastException
- if the class of the specified element prevents it from being added to this listNullPointerException
- if the specified element is null and this list does not permit null elementsIllegalArgumentException
- if some property of this element prevents it from being added to this listboolean remove(Object o)
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).remove
in interface Collection<E>
o
- element to be removed from this list, if presenttrue
if this list contained the specified elementClassCastException
- if the type of the specified element is incompatible with this list (optional)NullPointerException
- if the specified element is null and this list does not permit null elements (optional)UnsupportedOperationException
- if the remove
operation is not supported by this listboolean containsAll(Collection<?> c)
true
if this list contains all of the elements of the specified collection.containsAll
in interface Collection<E>
c
- collection to be checked for containment in this listtrue
if this list contains all of the elements of the specified collectionClassCastException
- if the types of one or more elements in the specified collection are incompatible with this list (optional)NullPointerException
- if the specified collection contains one or more null elements and this list does not permit null elements (optional), or if the specified collection is nullboolean addAll(Collection<? extends E> c)
addAll
in interface Collection<E>
c
- collection containing elements to be added to this listtrue
if this list changed as a result of the callUnsupportedOperationException
- if the addAll
operation is not supported by this listClassCastException
- if the class of an element of the specified collection prevents it from being added to this listNullPointerException
- if the specified collection contains one or more null elements and this list does not permit null elements, or if the specified collection is nullIllegalArgumentException
- if some property of an element of the specified collection prevents it from being added to this listboolean addAll(int index, Collection<? extends E> c)
index
- index at which to insert the first element from the specified collectionc
- collection containing elements to be added to this listtrue
if this list changed as a result of the callUnsupportedOperationException
- if the addAll
operation is not supported by this listClassCastException
- if the class of an element of the specified collection prevents it from being added to this listNullPointerException
- if the specified collection contains one or more null elements and this list does not permit null elements, or if the specified collection is nullIllegalArgumentException
- if some property of an element of the specified collection prevents it from being added to this listIndexOutOfBoundsException
- if the index is out of range (index < 0 || index > size()
)boolean removeAll(Collection<?> c)
removeAll
in interface Collection<E>
c
- collection containing elements to be removed from this listtrue
if this list changed as a result of the callUnsupportedOperationException
- if the removeAll
operation is not supported by this listClassCastException
- 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 nullboolean retainAll(Collection<?> c)
retainAll
in interface Collection<E>
c
- collection containing elements to be retained in this listtrue
if this list changed as a result of the callUnsupportedOperationException
- if the retainAll
operation is not supported by this listClassCastException
- 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 nulldefault void replaceAll(UnaryOperator<E> operator)
list
:
final ListIterator<E> li = list.listIterator();
while (li.hasNext()) {
li.set(operator.apply(li.next()));
}
If the list's list-iterator does not support the set
operation then an UnsupportedOperationException
will be thrown when replacing the first element.operator
- the operator to apply to each elementUnsupportedOperationException
- if this list is unmodifiable. Implementations may throw this exception if an element cannot be replaced or if, in general, modification is not supportedNullPointerException
- if the specified operator is null or if the operator result is a null value and this list does not permit null elements (optional)default void sort(Comparator<? super E> c)
Comparator
. 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 a ClassCastException
for any elements e1
and e2
in the list).
If the specified comparator is null
then all elements in this list must implement the Comparable
interface and the elements' natural ordering should be used.
This list must be modifiable, but need not be resizable.
The implementation takes equal advantage of ascending and descending order in its input array, and can take advantage of ascending and descending order in different parts of the same input array. It is well-suited to merging two or more sorted arrays: simply concatenate the arrays and sort the resulting array.
The implementation was adapted from Tim Peters's list sort for Python ( TimSort). It uses techniques from Peter McIlroy's "Optimistic Sorting and Information Theoretic Complexity", in Proceedings of the Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474, January 1993.
c
- the Comparator
used to compare list elements. A null
value indicates that the elements' natural ordering should be usedClassCastException
- if the list contains elements that are not mutually comparable using the specified comparatorUnsupportedOperationException
- if the list's list-iterator does not support the set
operationIllegalArgumentException
- (optional) if the comparator is found to violate the Comparator
contractvoid clear()
clear
in interface Collection<E>
UnsupportedOperationException
- if the clear
operation is not supported by this listboolean equals(Object o)
true
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 elements e1
and e2
are equal if Objects.equals(e1, e2)
.) In other words, two lists are defined to be equal if they contain the same elements in the same order. This definition ensures that the equals method works properly across different implementations of the List
interface.equals
in interface Collection<E>
equals
in class Object
o
- the object to be compared for equality with this listtrue
if the specified object is equal to this listint hashCode()
int hashCode = 1;
for (E e : list)
hashCode = 31*hashCode + (e==null ? 0 : e.hashCode());
This ensures that list1.equals(list2)
implies that list1.hashCode()==list2.hashCode()
for any two lists, list1
and list2
, as required by the general contract of Object.hashCode()
.hashCode
in interface Collection<E>
hashCode
in class Object
E get(int index)
index
- index of the element to returnIndexOutOfBoundsException
- if the index is out of range (index < 0 || index >= size()
)E set(int index, E element)
index
- index of the element to replaceelement
- element to be stored at the specified positionUnsupportedOperationException
- if the set
operation is not supported by this listClassCastException
- if the class of the specified element prevents it from being added to this listNullPointerException
- if the specified element is null and this list does not permit null elementsIllegalArgumentException
- if some property of the specified element prevents it from being added to this listIndexOutOfBoundsException
- if the index is out of range (index < 0 || index >= size()
)void add(int index, E element)
index
- index at which the specified element is to be insertedelement
- element to be insertedUnsupportedOperationException
- if the add
operation is not supported by this listClassCastException
- if the class of the specified element prevents it from being added to this listNullPointerException
- if the specified element is null and this list does not permit null elementsIllegalArgumentException
- if some property of the specified element prevents it from being added to this listIndexOutOfBoundsException
- if the index is out of range (index < 0 || index > size()
)E remove(int index)
index
- the index of the element to be removedUnsupportedOperationException
- if the remove
operation is not supported by this listIndexOutOfBoundsException
- if the index is out of range (index < 0 || index >= size()
)int indexOf(Object o)
i
such that Objects.equals(o, get(i))
, or -1 if there is no such index.o
- element to search forClassCastException
- if the type of the specified element is incompatible with this list (optional)NullPointerException
- if the specified element is null and this list does not permit null elements (optional)int lastIndexOf(Object o)
i
such that Objects.equals(o, get(i))
, or -1 if there is no such index.o
- element to search forClassCastException
- if the type of the specified element is incompatible with this list (optional)NullPointerException
- if the specified element is null and this list does not permit null elements (optional)ListIterator<E> listIterator()
ListIterator<E> listIterator(int index)
next
. An initial call to previous
would return the element with the specified index minus one.index
- index of the first element to be returned from the list iterator (by a call to next
)IndexOutOfBoundsException
- if the index is out of range (index < 0 || index > size()
)List<E> subList(int fromIndex, int toIndex)
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 supported by this list.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
and lastIndexOf
, 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.)
fromIndex
- low endpoint (inclusive) of the subListtoIndex
- high endpoint (exclusive) of the subListIndexOutOfBoundsException
- for an illegal endpoint index value (fromIndex < 0 || toIndex > size ||
fromIndex > toIndex
)default Spliterator<E> spliterator()
Spliterator
over the elements in this list. The Spliterator
reports Spliterator.SIZED
and Spliterator.ORDERED
. Implementations should document the reporting of additional characteristic values.
spliterator
in interface Collection<E>
spliterator
in interface Iterable<E>
RandomAccess
then the default implementation creates a spliterator that traverses elements by invoking the method get(int)
. If such invocation results or would result in an IndexOutOfBoundsException
then the spliterator will fail-fast and throw a ConcurrentModificationException
. If the list is also an instance of AbstractList
then the spliterator will use the list's modCount
field to provide additional fail-fast behavior. Iterator
. The spliterator inherits the fail-fast of the list's iterator. Spliterator
additionally reports Spliterator.SUBSIZED
.Spliterator
over the elements in this listdefault void addFirst(E e)
addFirst
in interface SequencedCollection<E>
add(0, e)
.e
- the element to be addedNullPointerException
- if the specified element is null and this collection does not permit null elementsUnsupportedOperationException
- if this collection implementation does not support this operationdefault void addLast(E e)
addLast
in interface SequencedCollection<E>
add(e)
.e
- the element to be added.NullPointerException
- if the specified element is null and this collection does not permit null elementsUnsupportedOperationException
- if this collection implementation does not support this operationdefault E getFirst()
getFirst
in interface SequencedCollection<E>
get(0)
. Otherwise, it throws NoSuchElementException
.NoSuchElementException
- if this collection is emptydefault E getLast()
getLast
in interface SequencedCollection<E>
get(size() - 1)
. Otherwise, it throws NoSuchElementException
.NoSuchElementException
- if this collection is emptydefault E removeFirst()
removeFirst
in interface SequencedCollection<E>
remove(0)
. Otherwise, it throws NoSuchElementException
.NoSuchElementException
- if this collection is emptyUnsupportedOperationException
- if this collection implementation does not support this operationdefault E removeLast()
removeLast
in interface SequencedCollection<E>
remove(size() - 1)
. Otherwise, it throws NoSuchElementException
.NoSuchElementException
- if this collection is emptyUnsupportedOperationException
- if this collection implementation does not support this operationdefault List<E> reversed()
reversed
in interface SequencedCollection<E>
reversed()
method of the view returns a reference to this List. Other operations on the view are implemented via calls to public methods on this List. The exact relationship between calls on the view and calls on this List is unspecified. However, order-sensitive operations generally delegate to the appropriate method with the opposite orientation. For example, calling getFirst
on the view results in a call to getLast
on this List.List
static <E> List<E> of()
E
- the List
's element typeList
static <E> List<E> of(E e1)
E
- the List
's element typee1
- the single elementList
containing the specified elementNullPointerException
- if the element is null
static <E> List<E> of(E e1, E e2)
E
- the List
's element typee1
- the first elemente2
- the second elementList
containing the specified elementsNullPointerException
- if an element is null
static <E> List<E> of(E e1, E e2, E e3)
E
- the List
's element typee1
- the first elemente2
- the second elemente3
- the third elementList
containing the specified elementsNullPointerException
- if an element is null
static <E> List<E> of(E e1, E e2, E e3, E e4)
E
- the List
's element typee1
- the first elemente2
- the second elemente3
- the third elemente4
- the fourth elementList
containing the specified elementsNullPointerException
- if an element is null
static <E> List<E> of(E e1, E e2, E e3, E e4, E e5)
E
- the List
's element typee1
- the first elemente2
- the second elemente3
- the third elemente4
- the fourth elemente5
- the fifth elementList
containing the specified elementsNullPointerException
- if an element is null
static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6)
E
- the List
's element typee1
- the first elemente2
- the second elemente3
- the third elemente4
- the fourth elemente5
- the fifth elemente6
- the sixth elementList
containing the specified elementsNullPointerException
- if an element is null
static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7)
E
- the List
's element typee1
- the first elemente2
- the second elemente3
- the third elemente4
- the fourth elemente5
- the fifth elemente6
- the sixth elemente7
- the seventh elementList
containing the specified elementsNullPointerException
- if an element is null
static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8)
E
- the List
's element typee1
- the first elemente2
- the second elemente3
- the third elemente4
- the fourth elemente5
- the fifth elemente6
- the sixth elemente7
- the seventh elemente8
- the eighth elementList
containing the specified elementsNullPointerException
- if an element is null
static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9)
E
- the List
's element typee1
- the first elemente2
- the second elemente3
- the third elemente4
- the fourth elemente5
- the fifth elemente6
- the sixth elemente7
- the seventh elemente8
- the eighth elemente9
- the ninth elementList
containing the specified elementsNullPointerException
- if an element is null
static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10)
E
- the List
's element typee1
- the first elemente2
- the second elemente3
- the third elemente4
- the fourth elemente5
- the fifth elemente6
- the sixth elemente7
- the seventh elemente8
- the eighth elemente9
- the ninth elemente10
- the tenth elementList
containing the specified elementsNullPointerException
- if an element is null
@SafeVarargs static <E> List<E> of(E... elements)
String[] array = ... ;
List<String[]> list = List.<String[]>of(array);
This will cause the List.of(E)
method to be invoked instead.E
- the List
's element typeelements
- the elements to be contained in the listList
containing the specified elementsNullPointerException
- if an element is null
or if the array is null
static <E> List<E> copyOf(Collection<? extends E> coll)
E
- the List
's element typecoll
- a Collection
from which elements are drawn, must be non-nullList
containing the elements of the given Collection
NullPointerException
- if coll is null, or if it contains any nulls
© 1993, 2023, Oracle and/or its affiliates. All rights reserved.
Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.
https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/List.html