java.util

Interface List<E>

All Superinterfaces:

Collection<E>, Iterable<E>

All Known Implementing Classes:

AbstractList, AbstractSequentialList, ArrayList, LinkedList, Stack, Vector

public interface List<E>
extends Collection<E>

An ordered collection (also known as a list). This collection allows access to elements by position, as well as control on where elements are inserted. Unlike sets, duplicate elements are permitted by this general contract (if a subclass forbids duplicates, this should be documented).

List places additional requirements on iterator, add, remove, equals, and hashCode, in addition to requiring more methods. List indexing is 0-based (like arrays), although some implementations may require time proportional to the index to obtain an arbitrary element. The List interface is incompatible with Set; you cannot implement both simultaneously.

Lists also provide a ListIterator which allows bidirectional traversal and other features atop regular iterators. Lists can be searched for arbitrary elements, and allow easy insertion and removal of multiple elements in one method call.

Note: While lists may contain themselves as elements, this leads to undefined (usually infinite recursive) behavior for some methods like hashCode or equals.

Since:

1.2

Author:

Original author unknown, Eric Blake (ebb9@email.byu.edu)

See Also:

Collection, Set, ArrayList, LinkedList, Vector, Arrays.asList(Object[]), Collections.nCopies(int, Object), Collections.EMPTY_LIST, AbstractList, AbstractSequentialList

Method Summary

Modifier and Type	Method and Description
boolean	add(E o) Add an element to the end of the list (optional operation).
void	add(int index, E o) Insert an element into the list at a given position (optional operation).
boolean	addAll(Collection<? extends E> c) Add the contents of a collection to the end of the list (optional operation).
boolean	addAll(int index, Collection<? extends E> c) Insert the contents of a collection into the list at a given position (optional operation).
void	clear() Clear the list, such that a subsequent call to isEmpty() would return true (optional operation).
boolean	contains(Object o) Test whether this list contains a given object as one of its elements.
boolean	containsAll(Collection<?> c) Test whether this list contains every element in a given collection.
boolean	equals(Object o) Test whether this list is equal to another object.
E	get(int index) Get the element at a given index in this list.
int	hashCode() Obtains a hash code for this list.
int	indexOf(Object o) Obtain the first index at which a given object is to be found in this list.
boolean	isEmpty() Test whether this list is empty, that is, if size() == 0.
Iterator<E>	iterator() Obtain an Iterator over this list, whose sequence is the list order.
int	lastIndexOf(Object o) Obtain the last index at which a given object is to be found in this list.
ListIterator<E>	listIterator() Obtain a ListIterator over this list, starting at the beginning.
ListIterator<E>	listIterator(int index) Obtain a ListIterator over this list, starting at a given position.
E	remove(int index) Remove the element at a given position in this list (optional operation).
boolean	remove(Object o) Remove the first occurence of an object from this list (optional operation).
boolean	removeAll(Collection<?> c) Remove all elements of a given collection from this list (optional operation).
boolean	retainAll(Collection<?> c) Remove all elements of this list that are not contained in a given collection (optional operation).
E	set(int index, E o) Replace an element of this list with another object (optional operation).
int	size() Get the number of elements in this list.
List<E>	subList(int fromIndex, int toIndex) Obtain a List view of a subsection of this list, from fromIndex (inclusive) to toIndex (exclusive).
Object[]	toArray() Copy the current contents of this list into an array.
<T> T[]	toArray(T[] a) Copy the current contents of this list into an array.

Method Detail

add

boolean add(E o)

Add an element to the end of the list (optional operation). If the list imposes restraints on what can be inserted, such as no null elements, this should be documented.

Specified by:

add in interface Collection<E>

Parameters:

o - the object to add

Returns:

true, as defined by Collection for a modified list

Throws:

UnsupportedOperationException - if this list does not support the add operation

ClassCastException - if o cannot be added to this list due to its type

IllegalArgumentException - if o cannot be added to this list for some other reason

NullPointerException - if o is null and this list doesn't support the addition of null values.

add

void add(int index,
         E o)

Insert an element into the list at a given position (optional operation). This shifts all existing elements from that position to the end one index to the right. This version of add has no return, since it is assumed to always succeed if there is no exception.

Parameters:

index - the location to insert the item

o - the object to insert

Throws:

UnsupportedOperationException - if this list does not support the add operation

IndexOutOfBoundsException - if index < 0 || index > size()

ClassCastException - if o cannot be added to this list due to its type

IllegalArgumentException - if o cannot be added to this list for some other reason

NullPointerException - if o is null and this list doesn't support the addition of null values.

addAll

boolean addAll(Collection<? extends E> c)

Add the contents of a collection to the end of the list (optional operation). This operation is undefined if this list is modified during the operation (for example, if you try to insert a list into itself).

Specified by:

addAll in interface Collection<E>

Parameters:

c - the collection to add

Returns:

true if the list was modified by this action, that is, if c is non-empty

Throws:

UnsupportedOperationException - if this list does not support the addAll operation

ClassCastException - if some element of c cannot be added to this list due to its type

IllegalArgumentException - if some element of c cannot be added to this list for some other reason

NullPointerException - if the specified collection is null

NullPointerException - if some element of c is null and this list doesn't support the addition of null values.

See Also:

add(Object)

addAll

boolean addAll(int index,
               Collection<? extends E> c)

Insert the contents of a collection into the list at a given position (optional operation). Shift all elements at that position to the right by the number of elements inserted. This operation is undefined if this list is modified during the operation (for example, if you try to insert a list into itself).

Parameters:

index - the location to insert the collection

c - the collection to insert

Returns:

true if the list was modified by this action, that is, if c is non-empty

Throws:

UnsupportedOperationException - if this list does not support the addAll operation

IndexOutOfBoundsException - if index < 0 || index > size()

ClassCastException - if some element of c cannot be added to this list due to its type

IllegalArgumentException - if some element of c cannot be added to this list for some other reason

NullPointerException - if some element of c is null and this list doesn't support the addition of null values.

NullPointerException - if the specified collection is null

See Also:

add(int, Object)

clear

void clear()

Clear the list, such that a subsequent call to isEmpty() would return true (optional operation).

Specified by:

clear in interface Collection<E>

Throws:

UnsupportedOperationException - if this list does not support the clear operation

contains

boolean contains(Object o)

Test whether this list contains a given object as one of its elements. This is defined as the existence of an element e such that o == null ? e == null : o.equals(e).

Specified by:

contains in interface Collection<E>

Parameters:

o - the element to look for

Returns:

true if this list contains the element

Throws:

ClassCastException - if the type of o is not a valid type for this list.

NullPointerException - if o is null and the list doesn't support null values.

containsAll

boolean containsAll(Collection<?> c)

Test whether this list contains every element in a given collection.

Specified by:

containsAll in interface Collection<E>

Parameters:

c - the collection to test for

Returns:

true if for every element o in c, contains(o) would return true

Throws:

NullPointerException - if the collection is null

ClassCastException - if the type of any element in c is not a valid type for this list.

NullPointerException - if some element of c is null and this list does not support null values.

See Also:

contains(Object)

equals

boolean equals(Object o)

Test whether this list is equal to another object. A List is defined to be equal to an object if and only if that object is also a List, and the two lists have the same sequence. Two lists l1 and l2 are equal if and only if l1.size() == l2.size(), and for every integer n between 0 and l1.size() - 1 inclusive, l1.get(n) == null ? l2.get(n) == null : l1.get(n).equals(l2.get(n)).

Specified by:

equals in interface Collection<E>

Overrides:

equals in class Object

Parameters:

o - the object to test for equality with this list

Returns:

true if o is equal to this list

See Also:

Object.equals(Object), hashCode()

get

E get(int index)

Get the element at a given index in this list.

Parameters:

index - the index of the element to be returned

Returns:

the element at index index in this list

Throws:

IndexOutOfBoundsException - if index < 0 || index >= size()

hashCode

int hashCode()

Obtains a hash code for this list. In order to obey the general contract of the hashCode method of class Object, this value is calculated as follows:

hashCode = 1;
Iterator i = list.iterator();
while (i.hasNext())
{
  Object obj = i.next();
  hashCode = 31 * hashCode + (obj == null ? 0 : obj.hashCode());
}

This ensures that the general contract of Object.hashCode() is adhered to.

Specified by:

hashCode in interface Collection<E>

Overrides:

hashCode in class Object

Returns:

the hash code of this list

See Also:

Object.hashCode(), equals(Object)

indexOf

int indexOf(Object o)

Obtain the first index at which a given object is to be found in this list.

Parameters:

o - the object to search for

Returns:

the least integer n such that o == null ? get(n) == null : o.equals(get(n)), or -1 if there is no such index.

Throws:

ClassCastException - if the type of o is not a valid type for this list.

NullPointerException - if o is null and this list does not support null values.

isEmpty

boolean isEmpty()

Test whether this list is empty, that is, if size() == 0.

Specified by:

isEmpty in interface Collection<E>

Returns:

true if this list contains no elements

iterator

Iterator<E> iterator()

Obtain an Iterator over this list, whose sequence is the list order.

Specified by:

iterator in interface Collection<E>

Specified by:

iterator in interface Iterable<E>

Returns:

an Iterator over the elements of this list, in order

lastIndexOf

int lastIndexOf(Object o)

Obtain the last index at which a given object is to be found in this list.

Returns:

the greatest integer n such that o == null ? get(n) == null : o.equals(get(n)), or -1 if there is no such index.

Throws:

ClassCastException - if the type of o is not a valid type for this list.

NullPointerException - if o is null and this list does not support null values.

listIterator

ListIterator<E> listIterator()

Obtain a ListIterator over this list, starting at the beginning.

Returns:

a ListIterator over the elements of this list, in order, starting at the beginning

listIterator

ListIterator<E> listIterator(int index)

Obtain a ListIterator over this list, starting at a given position. A first call to next() would return the same as get(index), and a first call to previous() would return the same as get(index - 1).

Parameters:

index - the position, between 0 and size() inclusive, to begin the iteration from

Returns:

a ListIterator over the elements of this list, in order, starting at index

Throws:

IndexOutOfBoundsException - if index < 0 || index > size()

remove

E remove(int index)

Remove the element at a given position in this list (optional operation). Shifts all remaining elements to the left to fill the gap.

Parameters:

index - the position within the list of the object to remove

Returns:

the object that was removed

Throws:

UnsupportedOperationException - if this list does not support the remove operation

IndexOutOfBoundsException - if index < 0 || index >= size()

remove

boolean remove(Object o)

Remove the first occurence of an object from this list (optional operation). That is, remove the first element e such that o == null ? e == null : o.equals(e).

Specified by:

remove in interface Collection<E>

Parameters:

o - the object to remove

Returns:

true if the list changed as a result of this call, that is, if the list contained at least one occurrence of o

Throws:

UnsupportedOperationException - if this list does not support the remove operation

ClassCastException - if the type of o is not a valid type for this list.

NullPointerException - if o is null and this list does not support removing null values.

removeAll

boolean removeAll(Collection<?> c)

Remove all elements of a given collection from this list (optional operation). That is, remove every element e such that c.contains(e).

Specified by:

removeAll in interface Collection<E>

Parameters:

c - the collection to filter out

Returns:

true if this list was modified as a result of this call

Throws:

UnsupportedOperationException - if this list does not support the removeAll operation

NullPointerException - if the collection is null

ClassCastException - if the type of any element in c is not a valid type for this list.

NullPointerException - if some element of c is null and this list does not support removing null values.

See Also:

remove(Object), contains(Object)

retainAll

boolean retainAll(Collection<?> c)

Remove all elements of this list that are not contained in a given collection (optional operation). That is, remove every element e such that !c.contains(e).

Specified by:

retainAll in interface Collection<E>

Parameters:

c - the collection to retain

Returns:

true if this list was modified as a result of this call

Throws:

UnsupportedOperationException - if this list does not support the retainAll operation

NullPointerException - if the collection is null

ClassCastException - if the type of any element in c is not a valid type for this list.

NullPointerException - if some element of c is null and this list does not support retaining null values.

See Also:

remove(Object), contains(Object)

set

E set(int index,
      E o)

Replace an element of this list with another object (optional operation).

Parameters:

index - the position within this list of the element to be replaced

o - the object to replace it with

Returns:

the object that was replaced

Throws:

UnsupportedOperationException - if this list does not support the set operation

IndexOutOfBoundsException - if index < 0 || index >= size()

ClassCastException - if o cannot be added to this list due to its type

IllegalArgumentException - if o cannot be added to this list for some other reason

NullPointerException - if o is null and this list does not support null values.

size

int size()

Get the number of elements in this list. If the list contains more than Integer.MAX_VALUE elements, return Integer.MAX_VALUE.

Specified by:

size in interface Collection<E>

Returns:

the number of elements in the list

subList

List<E> subList(int fromIndex,
                int toIndex)

Obtain a List view of a subsection of this list, from fromIndex (inclusive) to toIndex (exclusive). If the two indices are equal, the sublist is empty. The returned list should be modifiable if and only if this list is modifiable. Changes to the returned list should be reflected in this list. If this list is structurally modified in any way other than through the returned list, the result of any subsequent operations on the returned list is undefined.

Parameters:

fromIndex - the index that the returned list should start from (inclusive)

toIndex - the index that the returned list should go to (exclusive)

Returns:

a List backed by a subsection of this list

Throws:

IndexOutOfBoundsException - if fromIndex < 0 || toIndex > size() || fromIndex > toIndex

toArray

Object[] toArray()

Copy the current contents of this list into an array.

Specified by:

toArray in interface Collection<E>

Returns:

an array of type Object[] and length equal to the length of this list, containing the elements currently in this list, in order

toArray

<T> T[] toArray(T[] a)

Copy the current contents of this list into an array. If the array passed as an argument has length less than that of this list, an array of the same run-time type as a, and length equal to the length of this list, is allocated using Reflection. Otherwise, a itself is used. The elements of this list are copied into it, and if there is space in the array, the following element is set to null. The resultant array is returned. Note: The fact that the following element is set to null is only useful if it is known that this list does not contain any null elements.

Specified by:

toArray in interface Collection<E>

Parameters:

a - the array to copy this list into

Returns:

an array containing the elements currently in this list, in order

Throws:

ArrayStoreException - if the type of any element of the collection is not a subtype of the element type of a

NullPointerException - if the specified array is null