E - the type of elements in this listpublic interface List<E> extends Collection<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.
This interface is a member of the Java Collections Framework
Collection,
Set,
ArrayList,
Vector,
AbstractList| Modifier and Type | Method and Description |
|---|---|
boolean |
add(E e)
Appends the specified element to the end of this list (optional operation).
|
void |
add(int index,
E element)
Inserts the specified element at the specified position in this list (optional operation).
|
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 (optional operation).
|
boolean |
addAll(int index,
Collection<? extends E> c)
Inserts all of the elements in the specified collection into this list at the specified position
(optional operation).
|
void |
clear()
Removes all of the elements from this list (optional operation).
|
boolean |
contains(Object o)
Returns true if this list contains the specified element.
|
boolean |
containsAll(Collection<?> c)
Returns true if this list contains all of the elements of the specified collection.
|
boolean |
equals(Object o)
Compares the specified object with this list for equality.
|
E |
get(int index)
Returns the element at the specified position in this list.
|
int |
hashCode()
Returns the hash code value for 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 true if this list contains no elements.
|
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 (optional operation).
|
boolean |
remove(Object o)
Removes the first occurrence of the specified element from this list, if it is present (optional
operation).
|
boolean |
removeAll(Collection<?> c)
Removes from this list all of its elements that are contained in the specified collection
(optional operation).
|
boolean |
retainAll(Collection<?> c)
Retains only the elements in this list that are contained in the specified collection (optional
operation).
|
E |
set(int index,
E element)
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.
|
List<E> |
subList(int fromIndex,
int toIndex)
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(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.
|
boolean 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 listCollection.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 listvoid 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())boolean addAll(Collection<? extends E> c)
addAll in interface Collection<E>c - collection containing elements to be added to this listUnsupportedOperationException - 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 listadd(Object)boolean 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 listUnsupportedOperationException - 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())void clear()
clear in interface Collection<E>UnsupportedOperationException - if the clear operation is not supported by this listboolean contains(Object o)
contains in interface Collection<E>o - element whose presence in this list is to be testedClassCastException - 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)boolean containsAll(Collection<?> c)
containsAll in interface Collection<E>c - collection to be checked for containment in this listClassCastException - 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 nullcontains(Object)boolean equals(@Nullable Object o)
equals in interface Collection<E>equals in class Objecto - the object to be compared for equality with this listObject.hashCode(),
HashMapE get(int index)
index - index of the element to returnIndexOutOfBoundsException - if the index is out of range (index < 0 || index >= size())int 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 ObjectObject.equals(Object),
equals(Object)int indexOf(Object o)
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)boolean isEmpty()
isEmpty in interface Collection<E>Iterator<E> iterator()
int lastIndexOf(Object o)
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())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())boolean remove(Object o)
remove in interface Collection<E>o - element to be removed from this list, if presentClassCastException - 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 removeAll(Collection<?> c)
removeAll in interface Collection<E>c - collection containing elements to be removed from this listUnsupportedOperationException - 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 nullremove(Object),
contains(Object)boolean retainAll(Collection<?> c)
retainAll in interface Collection<E>c - collection containing elements to be retained in this listUnsupportedOperationException - 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 nullremove(Object),
contains(Object)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())int size()
size in interface Collection<E>List<E> subList(int fromIndex, int toIndex)
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)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 runtime 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 null