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Overview Package Class Use Tree Deprecated Index Help
JavaTM 2 Platform
Standard Ed. 5.0 PREV CLASS NEXT CLASS FRAMES NO FRAMES All Classes All
Classes SUMMARY: NESTED | FIELD | CONSTR | METHOD
DETAIL: FIELD | CONSTR | METHOD
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JAVA.UTIL
INTERFACE LIST<E>
All Superinterfaces: Collection<E>, Iterable<E> All Known Implementing Classes:
AbstractList, AbstractSequentialList, ArrayList, AttributeList,
CopyOnWriteArrayList, LinkedList, RoleList, RoleUnresolvedList, Stack, Vector
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public interface List<E>extends Collection<E>
An ordered collection (also known as a sequence). The user of this interface has
precise control over where in the list each element is inserted. The user can
access elements by their integer index (position in the list), and search for
elements in the list.
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 a 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.
Since: 1.2 See Also:Collection, Set, ArrayList, LinkedList, Vector,
Arrays.asList(Object[]), Collections.nCopies(int, Object),
Collections.EMPTY_LIST, AbstractList, AbstractSequentialList
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Method Summary boolean add(E o)
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 in this list of the first occurrence of the
specified element, or -1 if this list does not contain this 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 in this list of the last occurrence of the specified
element, or -1 if this list does not contain this element. ListIterator<E>
listIterator()
Returns a list iterator of the elements in this list (in proper
sequence). ListIterator<E> listIterator(int index)
Returns a list iterator of the elements in this list (in proper
sequence), starting at the specified position in this 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 in this list of the specified element
(optional operation). boolean removeAll(Collection<?> c)
Removes from this list all the 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.
<T> T[]
toArray(T[] a)
Returns an array containing all of the elements in this list in proper
sequence; the runtime type of the returned array is that of the specified array.
Method Detail
SIZE
int size()
Returns the number of elements in this list. If this list contains more than
Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.
Specified by:size in interface Collection<E> Returns:the number of elements in
this list.
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ISEMPTY
boolean isEmpty()
Returns true if this list contains no elements.
Specified by:isEmpty in interface Collection<E> Returns:true if this list
contains no elements.
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CONTAINS
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
(o==null ? e==null : o.equals(e)).
Specified by:contains in interface Collection<E> Parameters:o - element whose
presence in this list is to be tested. Returns:true if this list contains the
specified element. Throws: ClassCastException - 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 support null elements
(optional).
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ITERATOR
Iterator<E> iterator()
Returns an iterator over the elements in this list in proper sequence.
Specified by:iterator in interface Collection<E>Specified by:iterator in
interface Iterable<E> Returns:an iterator over the elements in this list in
proper sequence.
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TOARRAY
Object[] toArray()
Returns an array containing all of the elements in this list in proper sequence.
Obeys the general contract of the Collection.toArray method.
Specified by:toArray in interface Collection<E> Returns:an array containing all
of the elements in this list in proper sequence.See Also:Arrays.asList(Object[])
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TOARRAY
<T> T[] toArray(T[] a)
Returns an array containing all of the elements in this list in proper sequence;
the runtime type of the returned array is that of the specified array. Obeys the
general contract of the Collection.toArray(Object[]) method.
Specified by:toArray in interface Collection<E> Parameters:a - 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.
Returns:an array containing the elements of this 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.
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ADD
boolean add(E o)
Appends the specified element to the end of this list (optional operation).
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.
Specified by:add in interface Collection<E> Parameters:o - element to be
appended to this list. Returns:true (as per the general contract of the
Collection.add method). Throws: UnsupportedOperationException - if the add
method is not supported by this list. ClassCastException - if the class of the
specified element prevents it from being added to this list.
NullPointerException - if the specified element is null and this list does not
support null elements. IllegalArgumentException - if some aspect of this element
prevents it from being added to this list.
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REMOVE
boolean remove(Object o)
Removes the first occurrence in this list of the specified element (optional
operation). If this list does not contain the element, it is unchanged. More
formally, removes the element with the lowest index i such that (o==null ?
get(i)==null : o.equals(get(i))) (if such an element exists).
Specified by:remove in interface Collection<E> Parameters:o - element to be
removed from this list, if present. Returns:true if this list contained the
specified element. Throws: ClassCastException - 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 support null elements
(optional). UnsupportedOperationException - if the remove method is not
supported by this list.
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CONTAINSALL
boolean containsAll(Collection<?> c)
Returns true if this list contains all of the elements of the specified
collection.
Specified by:containsAll in interface Collection<E> Parameters:c - collection to
be checked for containment in this list. Returns:true if this list contains all
of the elements of the specified collection. Throws: ClassCastException - 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 support null elements
(optional). NullPointerException - if the specified collection is null.See
Also:contains(Object)
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ADDALL
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). The behavior of this operation is unspecified if the
specified collection is modified while the operation is in progress. (Note that
this will occur if the specified collection is this list, and it's nonempty.)
Specified by:addAll in interface Collection<E> Parameters:c - collection whose
elements are to be added to this list. Returns:true if this list changed as a
result of the call. Throws: UnsupportedOperationException - if the addAll method
is not supported by this list. ClassCastException - if the class of an element
in the specified collection prevents it from being added to this list.
NullPointerException - if the specified collection contains one or more null
elements and this list does not support null elements, or if the specified
collection is null. IllegalArgumentException - if some aspect of an element in
the specified collection prevents it from being added to this list.See
Also:add(Object)
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ADDALL
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). 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 this list in the order that they are
returned by the specified collection's iterator. The behavior of this operation
is unspecified if the specified collection is modified while the operation is in
progress. (Note that this will occur if the specified collection is this list,
and it's nonempty.)
Parameters:index - index at which to insert first element from the specified
collection.c - elements to be inserted into this list. Returns:true if this list
changed as a result of the call. Throws: UnsupportedOperationException - if the
addAll method is not supported by this list. ClassCastException - if the class
of one of elements of the specified collection prevents it from being added to
this list. NullPointerException - if the specified collection contains one or
more null elements and this list does not support null elements, or if the
specified collection is null. IllegalArgumentException - if some aspect of one
of elements of the specified collection prevents it from being added to this
list. IndexOutOfBoundsException - if the index is out of range (index < 0 ||
index > size()).
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REMOVEALL
boolean removeAll(Collection<?> c)
Removes from this list all the elements that are contained in the specified
collection (optional operation).
Specified by:removeAll in interface Collection<E> Parameters:c - collection that
defines which elements will be removed from this list. Returns:true if this list
changed as a result of the call. Throws: UnsupportedOperationException - if the
removeAll method is not supported by this list. ClassCastException - if the
types of one or more elements in this list are incompatible with the specified
collection (optional). NullPointerException - if this list contains one or more
null elements and the specified collection does not support null elements
(optional). NullPointerException - if the specified collection is null.See
Also:remove(Object), contains(Object)
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RETAINALL
boolean retainAll(Collection<?> c)
Retains only the elements in this list that are contained in the specified
collection (optional operation). In other words, removes from this list all the
elements that are not contained in the specified collection.
Specified by:retainAll in interface Collection<E> Parameters:c - collection that
defines which elements this set will retain. Returns:true if this list changed
as a result of the call. Throws: UnsupportedOperationException - if the
retainAll method is not supported by this list. ClassCastException - if the
types of one or more elements in this list are incompatible with the specified
collection (optional). NullPointerException - if this list contains one or more
null elements and the specified collection does not support null elements
(optional). NullPointerException - if the specified collection is null.See
Also:remove(Object), contains(Object)
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CLEAR
void clear()
Removes all of the elements from this list (optional operation). This list will
be empty after this call returns (unless it throws an exception).
Specified by:clear in interface Collection<E> Throws:
UnsupportedOperationException - if the clear method is not supported by this
list.
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EQUALS
boolean equals(Object o)
Compares the specified object with this list for equality. Returns 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 (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. This definition ensures that the equals method works properly across
different implementations of the List interface.
Specified by:equals in interface Collection<E>Overrides:equals in class Object
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:Object.hashCode(), Hashtable
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HASHCODE
int hashCode()
Returns the hash code value for this list. The hash code of a list is defined to
be the result of the following calculation:
hashCode = 1;
Iterator i = list.iterator();
while (i.hasNext()) {
Object obj = i.next();
hashCode = 31*hashCode + (obj==null ? 0 : obj.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.
Specified by:hashCode in interface Collection<E>Overrides:hashCode in class
Object Returns:the hash code value for this list.See Also:Object.hashCode(),
Object.equals(Object), equals(Object)
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GET
E get(int index)
Returns the element at the specified position in this list.
Parameters:index - index of 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()).
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SET
E set(int index,
E element)
Replaces the element at the specified position in this list with the specified
element (optional operation).
Parameters:index - index of element to replace.element - element to be stored at
the specified position. Returns:the element previously at the specified
position. Throws: UnsupportedOperationException - if the set method is not
supported by this list. ClassCastException - if the class of the specified
element prevents it from being added to this list. NullPointerException - if the
specified element is null and this list does not support null elements.
IllegalArgumentException - if some aspect of the specified element prevents it
from being added to this list. IndexOutOfBoundsException - if the index is out
of range (index < 0 || index >= size()).
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ADD
void add(int index,
E element)
Inserts the specified element at the specified position in this list (optional
operation). Shifts the element currently at that position (if any) and any
subsequent elements to the right (adds one to their indices).
Parameters:index - index at which the specified element is to be
inserted.element - element to be inserted. Throws: UnsupportedOperationException
- if the add method is not supported by this list. ClassCastException - if the
class of the specified element prevents it from being added to this list.
NullPointerException - if the specified element is null and this list does not
support null elements. IllegalArgumentException - if some aspect of the
specified element prevents it from being added to this list.
IndexOutOfBoundsException - if the index is out of range (index < 0 || index >
size()).
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REMOVE
E remove(int index)
Removes the element at the specified position in this list (optional operation).
Shifts any subsequent elements to the left (subtracts one from their indices).
Returns the element that was removed from the list.
Parameters:index - the index of the element to removed. Returns:the element
previously at the specified position. Throws: UnsupportedOperationException - if
the remove method is not supported by this list. IndexOutOfBoundsException - if
the index is out of range (index < 0 || index >= size()).
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INDEXOF
int indexOf(Object o)
Returns the index in this list of the first occurrence of the specified element,
or -1 if this list does not contain this element. More formally, returns the
lowest index i such that (o==null ? get(i)==null : o.equals(get(i))), or -1 if
there is no such index.
Parameters:o - element to search for. Returns:the index in this list of the
first occurrence of the specified element, or -1 if this list does not contain
this element. Throws: ClassCastException - 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 support null elements
(optional).
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LASTINDEXOF
int lastIndexOf(Object o)
Returns the index in this list of the last occurrence of the specified element,
or -1 if this list does not contain this element. More formally, returns the
highest index i such that (o==null ? get(i)==null : o.equals(get(i))), or -1 if
there is no such index.
Parameters:o - element to search for. Returns:the index in this list of the last
occurrence of the specified element, or -1 if this list does not contain this
element. Throws: ClassCastException - 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 support null elements (optional).
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LISTITERATOR
ListIterator<E> listIterator()
Returns a list iterator of the elements in this list (in proper sequence).
Returns:a list iterator of the elements in this list (in proper sequence).
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LISTITERATOR
ListIterator<E> listIterator(int index)
Returns a list iterator of the elements in this list (in proper sequence),
starting at the specified position in this list. The specified index indicates
the first element that would be returned by an initial call to the next method.
An initial call to the previous method would return the element with the
specified index minus one.
Parameters:index - index of first element to be returned from the list iterator
(by a call to the next method). Returns:a list iterator of the elements in this
list (in proper sequence), starting at the specified position in this list.
Throws: IndexOutOfBoundsException - if the index is out of range (index < 0 ||
index > size()).
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SUBLIST
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
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.)
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 - for an illegal endpoint
index value (fromIndex < 0 || toIndex > size || fromIndex > toIndex).
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Overview Package Class Use Tree Deprecated Index Help
JavaTM 2 Platform
Standard Ed. 5.0 PREV CLASS NEXT CLASS FRAMES NO FRAMES All Classes All
Classes SUMMARY: NESTED | FIELD | CONSTR | METHOD
DETAIL: FIELD | CONSTR | METHOD
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