AbstractList
public
abstract
class
AbstractList
extends AbstractCollection<E>
implements
List<E>
java.lang.Object | ||
↳ | java.util.AbstractCollection<E> | |
↳ | java.util.AbstractList<E> |
This class provides a skeletal implementation of the List
interface to minimize the effort required to implement this interface
backed by a "random access" data store (such as an array). For sequential
access data (such as a linked list), AbstractSequentialList
should
be used in preference to this class.
To implement an unmodifiable list, the programmer needs only to extend
this class and provide implementations for the get(int)
and
size()
methods.
To implement a modifiable list, the programmer must additionally
override the set(int, E)
method (which otherwise
throws an UnsupportedOperationException
). If the list is
variable-size the programmer must additionally override the
add(int, E)
and remove(int)
methods.
The programmer should generally provide a void (no argument) and collection
constructor, as per the recommendation in the Collection
interface
specification.
Unlike the other abstract collection implementations, the programmer does
not have to provide an iterator implementation; the iterator and
list iterator are implemented by this class, on top of the "random access"
methods:
get(int)
,
set(int, E)
,
add(int, E)
and
remove(int)
.
The documentation for each non-abstract method in this class describes its implementation in detail. Each of these methods may be overridden if the collection being implemented admits a more efficient implementation.
This class is a member of the Java Collections Framework.
Summary
Fields | |
---|---|
protected
int |
modCount
The number of times this list has been structurally modified. |
Protected constructors | |
---|---|
AbstractList()
Sole constructor. |
Public methods | |
---|---|
void
|
add(int index, E element)
Inserts the specified element at the specified position in this list (optional operation). |
boolean
|
add(E e)
Appends the specified element to the end of this list (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
|
equals(Object o)
Compares the specified object with this list for equality. |
abstract
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. |
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(int index)
Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list. |
ListIterator<E>
|
listIterator()
Returns a list iterator over the elements in this list (in proper sequence). |
E
|
remove(int index)
Removes the element at the specified position in this list (optional operation). |
E
|
set(int index, E element)
Replaces the element at the specified position in this list with the specified element (optional operation). |
List<E>
|
subList(int fromIndex, int toIndex)
Returns a view of the portion of this list between the specified
|
Protected methods | |
---|---|
void
|
removeRange(int fromIndex, int toIndex)
Removes from this list all of the elements whose index is between
|
Inherited methods | |
---|---|
Fields
modCount
protected int modCount
The number of times this list has been structurally modified. Structural modifications are those that change the size of the list, or otherwise perturb it in such a fashion that iterations in progress may yield incorrect results.
This field is used by the iterator and list iterator implementation
returned by the iterator
and listIterator
methods.
If the value of this field changes unexpectedly, the iterator (or list
iterator) will throw a ConcurrentModificationException
in
response to the next
, remove
, previous
,
set
or add
operations. This provides
fail-fast behavior, rather than non-deterministic behavior in
the face of concurrent modification during iteration.
Use of this field by subclasses is optional. If a subclass
wishes to provide fail-fast iterators (and list iterators), then it
merely has to increment this field in its add(int, E)
and
remove(int)
methods (and any other methods that it overrides
that result in structural modifications to the list). A single call to
add(int, E)
or remove(int)
must add no more than
one to this field, or the iterators (and list iterators) will throw
bogus ConcurrentModificationExceptions
. If an implementation
does not wish to provide fail-fast iterators, this field may be
ignored.
Protected constructors
AbstractList
protected AbstractList ()
Sole constructor. (For invocation by subclass constructors, typically implicit.)
Public methods
add
public 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).
Implementation Requirements:
- This implementation always throws an
UnsupportedOperationException
.
Parameters | |
---|---|
index |
int : index at which the specified element is to be inserted |
element |
E : element to be inserted |
Throws | |
---|---|
UnsupportedOperationException |
|
ClassCastException |
|
NullPointerException |
|
IllegalArgumentException |
|
IndexOutOfBoundsException |
add
public boolean add (E e)
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.
Implementation Requirements:
- This implementation calls
add(size(), e)
.Note that this implementation throws an
UnsupportedOperationException
unlessadd(int, E)
is overridden.
Parameters | |
---|---|
e |
E : element to be appended to this list |
Returns | |
---|---|
boolean |
true (as specified by Collection#add ) |
Throws | |
---|---|
UnsupportedOperationException |
if the add operation
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 permit null elements |
IllegalArgumentException |
if some property of this element prevents it from being added to this list |
addAll
public 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 undefined 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.)
Implementation Requirements:
- This implementation gets an iterator over the specified collection
and iterates over it, inserting the elements obtained from the
iterator into this list at the appropriate position, one at a time,
using
add(int, E)
. Many implementations will override this method for efficiency.Note that this implementation throws an
UnsupportedOperationException
unlessadd(int, E)
is overridden.
Parameters | |
---|---|
index |
int : index at which to insert the first element from the
specified collection |
c |
Collection : collection containing elements to be added to this list |
Returns | |
---|---|
boolean |
true if this list changed as a result of the call |
Throws | |
---|---|
UnsupportedOperationException |
|
ClassCastException |
|
NullPointerException |
|
IllegalArgumentException |
|
IndexOutOfBoundsException |
clear
public void clear ()
Removes all of the elements from this list (optional operation). The list will be empty after this call returns.
Implementation Requirements:
- This implementation calls
removeRange(0, size())
.Note that this implementation throws an
UnsupportedOperationException
unlessremove(int index)
orremoveRange(int fromIndex, int toIndex)
is overridden.
Throws | |
---|---|
UnsupportedOperationException |
if the clear operation
is not supported by this list |
equals
public 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.
Implementation Requirements:
- This implementation first checks if the specified object is this
list. If so, it returns
true
; if not, it checks if the specified object is a list. If not, it returnsfalse
; if so, it iterates over both lists, comparing corresponding pairs of elements. If any comparison returnsfalse
, this method returnsfalse
. If either iterator runs out of elements before the other it returnsfalse
(as the lists are of unequal length); otherwise it returnstrue
when the iterations complete.
Parameters | |
---|---|
o |
Object : the object to be compared for equality with this list |
Returns | |
---|---|
boolean |
true if the specified object is equal to this list |
get
public abstract E get (int index)
Returns the element at the specified position in this list.
Parameters | |
---|---|
index |
int : index of the element to return |
Returns | |
---|---|
E |
the element at the specified position in this list |
Throws | |
---|---|
IndexOutOfBoundsException |
hashCode
public int hashCode ()
Returns the hash code value for this list.
Implementation Requirements:
- This implementation uses exactly the code that is used to define the
list hash function in the documentation for the
List#hashCode
method.
Returns | |
---|---|
int |
the hash code value for this list |
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.
Implementation Requirements:
- This implementation first gets a list iterator (with
listIterator()
). Then, it iterates over the list until the specified element is found or the end of the list is reached.
Parameters | |
---|---|
o |
Object : element to search for |
Returns | |
---|---|
int |
the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element |
Throws | |
---|---|
ClassCastException |
|
NullPointerException |
iterator
public Iterator<E> iterator ()
Returns an iterator over the elements in this list in proper sequence.
Implementation Requirements:
- This implementation returns a straightforward implementation of the
iterator interface, relying on the backing list's
size()
,get(int)
, andremove(int)
methods.Note that the iterator returned by this method will throw an
UnsupportedOperationException
in response to itsremove
method unless the list'sremove(int)
method is overridden.This implementation can be made to throw runtime exceptions in the face of concurrent modification, as described in the specification for the (protected)
modCount
field.
Returns | |
---|---|
Iterator<E> |
an iterator over the elements in this list in proper sequence |
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.
Implementation Requirements:
- This implementation first gets a list iterator that points to the end
of the list (with
listIterator(size())
). Then, it iterates backwards over the list until the specified element is found, or the beginning of the list is reached.
Parameters | |
---|---|
o |
Object : element to search for |
Returns | |
---|---|
int |
the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element |
Throws | |
---|---|
ClassCastException |
|
NullPointerException |
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.
Implementation Requirements:
- This implementation returns a straightforward implementation of the
ListIterator
interface that extends the implementation of theIterator
interface returned by theiterator()
method. TheListIterator
implementation relies on the backing list'sget(int)
,set(int, E)
,add(int, E)
andremove(int)
methods.Note that the list iterator returned by this implementation will throw an
UnsupportedOperationException
in response to itsremove
,set
andadd
methods unless the list'sremove(int)
,set(int, E)
, andadd(int, E)
methods are overridden.This implementation can be made to throw runtime exceptions in the face of concurrent modification, as described in the specification for the (protected)
modCount
field.
Parameters | |
---|---|
index |
int : index of the first element to be returned from the
list iterator (by a call to next ) |
Returns | |
---|---|
ListIterator<E> |
a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list |
Throws | |
---|---|
IndexOutOfBoundsException |
listIterator
public ListIterator<E> listIterator ()
Returns a list iterator over the elements in this list (in proper sequence).
Implementation Requirements:
- This implementation returns
listIterator(0)
.
Returns | |
---|---|
ListIterator<E> |
a list iterator over the elements in this list (in proper sequence) |
See also:
remove
public 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.
Implementation Requirements:
- This implementation always throws an
UnsupportedOperationException
.
Parameters | |
---|---|
index |
int : the index of the element to be removed |
Returns | |
---|---|
E |
the element previously at the specified position |
Throws | |
---|---|
UnsupportedOperationException |
|
IndexOutOfBoundsException |
set
public E set (int index, E element)
Replaces the element at the specified position in this list with the specified element (optional operation).
Implementation Requirements:
- This implementation always throws an
UnsupportedOperationException
.
Parameters | |
---|---|
index |
int : index of the element to replace |
element |
E : element to be stored at the specified position |
Returns | |
---|---|
E |
the element previously at the specified position |
Throws | |
---|---|
UnsupportedOperationException |
|
ClassCastException |
|
NullPointerException |
|
IllegalArgumentException |
|
IndexOutOfBoundsException |
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 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();
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.)
Implementation Requirements:
- This implementation returns a list that subclasses
AbstractList
. The subclass stores, in private fields, the size of the subList (which can change over its lifetime), and the expectedmodCount
value of the backing list. There are two variants of the subclass, one of which implementsRandomAccess
. If this list implementsRandomAccess
the returned list will be an instance of the subclass that implementsRandomAccess
.The subclass's
set(int, E)
,get(int)
,add(int, E)
,remove(int)
,addAll(int, Collection)
andremoveRange(int, int)
methods all delegate to the corresponding methods on the backing abstract list, after bounds-checking the index and adjusting for the offset. TheaddAll(Collection c)
method merely returnsaddAll(size, c)
.The
listIterator(int)
method returns a "wrapper object" over a list iterator on the backing list, which is created with the corresponding method on the backing list. Theiterator
method merely returnslistIterator()
, and thesize
method merely returns the subclass'ssize
field.All methods first check to see if the actual
modCount
of the backing list is equal to its expected value, and throw aConcurrentModificationException
if it is not.
Parameters | |
---|---|
fromIndex |
int : low endpoint (inclusive) of the subList |
toIndex |
int : high endpoint (exclusive) of the subList |
Returns | |
---|---|
List<E> |
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) |
Protected methods
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.)
This method is called by the clear
operation on this list
and its subLists. Overriding this method to take advantage of
the internals of the list implementation can substantially
improve the performance of the clear
operation on this list
and its subLists.
Implementation Requirements:
- This implementation gets a list iterator positioned before
fromIndex
, and repeatedly callsListIterator.next
followed byListIterator.remove
until the entire range has been removed. Note: ifListIterator.remove
requires linear time, this implementation requires quadratic time.
Parameters | |
---|---|
fromIndex |
int : index of first element to be removed |
toIndex |
int : index after last element to be removed |