java.util.AbstractCollection<E>
java.util.AbstractList<E>
is new.
java.lang.Object
public abstract class AbstractList<E>
This class provides a skeletal implementation of the
List
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
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)
get(int index)
and
size()
size()
methods.
To implement a modifiable list, the programmer must additionally override the
set(int, E)
set(int index, Object element)
method (which otherwise throws an
UnsupportedOperationException).
UnsupportedOperationException
.
If the list is variable-size the programmer must additionally override the
add(int, E)
add(int index, Object element)
and
remove(int)
remove(int index)
methods.
The programmer should generally provide a void (no argument) and collection constructor, as per the recommendation in the
Collection
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)
get(int index)
,
set(int, E)
set(int index, E element)
,
add(int, E)
add(int index, E element)
and
remove(int)
remove(int index)
.
The documentation for each non-abstract
method
methods
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
Java Collections Framework
.
| Field Summary | |
|---|---|
| protected int |
modCount
The number of times this list has been structurally modified . |
| Constructor Summary | |
|---|---|
| protected |
AbstractList
() Sole constructor. |
| Method Summary | |
|---|---|
| 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
(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
() Returns a list iterator over 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). |
| protected void |
removeRange
(int fromIndex, int toIndex) Removes from this list all of the elements whose index is between
fromIndex,
toIndex,
|
| 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 fromIndex , inclusive, and toIndex , exclusive. |
| Methods inherited from class java.util. AbstractCollection |
|---|
| addAll , contains , containsAll , isEmpty , remove , removeAll , retainAll , size , toArray , toArray , toString |
| Methods inherited from class java.lang. Object |
|---|
| clone , finalize , getClass , notify , notifyAll , wait , wait , wait |
| Methods inherited from interface java.util. List |
|---|
| addAll , contains , containsAll , isEmpty , remove , removeAll , retainAll , size , toArray , toArray |
| Field Detail |
|---|
protected transient int modCount
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,
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)
Object)
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)
Object)
or
remove(int)
must add no more than one to this field, or the iterators (and list iterators) will throw bogus
ConcurrentModificationExceptions.
ConcurrentModificationExceptions
.
If an implementation does not wish to provide fail-fast iterators, this field may be ignored.
| Constructor Detail |
|---|
protected AbstractList()
| Method Detail |
|---|
public 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.
This implementation calls
add(size(),
e).
e)
.
Note that this implementation throws an
UnsupportedOperationException
unless
add(int, E)
add(int, Object)
is overridden.
public abstract E get(int index)
public E set(int index,
E element)
This implementation always throws an
UnsupportedOperationException.
UnsupportedOperationException
.
public void add(int index,
E element)
This implementation always throws an
UnsupportedOperationException.
UnsupportedOperationException
.
public E remove(int index)
This implementation always throws an
UnsupportedOperationException.
UnsupportedOperationException
.
public int indexOf(Object o)
This implementation first gets a list iterator (with
listIterator()).
listIterator()
).
Then, it iterates over the list until the specified element is found or the end of the list is reached.
public int lastIndexOf(Object o)
This implementation first gets a list iterator that points to the end of the list (with
listIterator(size())).
listIterator(size())
).
Then, it iterates backwards over the list until the specified element is found, or the beginning of the list is reached.
public void clear()
This implementation calls
removeRange(0,
size()).
size())
.
Note that this implementation throws an UnsupportedOperationException unless remove(int index) or removeRange(int fromIndex, int toIndex) is overridden.
public boolean addAll(int index,
Collection<? extends E> c)
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).
Object)
.
Many implementations will override this method for efficiency.
Note that this implementation throws an
UnsupportedOperationException
unless
add(int, E)
add(int, Object)
is overridden.
public Iterator<E> iterator()
This implementation returns a straightforward implementation of the iterator interface, relying on the backing list's
size(), get(int),
size()
,
get(int)
,
and
remove(int)
methods.
Note that the iterator returned by this method will throw an UnsupportedOperationException in response to its remove method unless the list's remove(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.
public ListIterator<E> listIterator()
This implementation returns
listIterator(0).
listIterator(0)
.
public ListIterator<E> listIterator(int index)
This implementation returns a straightforward implementation of the
ListIterator
interface that extends the implementation of the
Iterator
interface returned by the
iterator()
method. The
ListIterator
implementation relies on the backing list's
get(int),
get(int)
,
set(int,
E),
Object)
,
add(int,
E)
Object)
and
remove(int)
methods.
Note that the list iterator returned by this implementation will throw an
UnsupportedOperationException
in response to its
remove,
remove
,
set
and
add
methods unless the list's
remove(int),
remove(int)
,
set(int,
E),
Object)
,
and
add(int,
E)
Object)
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.
public 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.)
This implementation returns a list that subclasses
AbstractList.
AbstractList
.
The subclass stores, in private fields, the offset of the subList within the backing list, the size of the subList (which can change over its lifetime), and the expected
modCount
value of the backing list. There are two variants of the subclass, one of which implements
RandomAccess.
RandomAccess
.
If this list implements
RandomAccess
the returned list will be an instance of the subclass that implements
RandomAccess.
RandomAccess
.
The subclass's
set(int,
E), get(int),
Object)
,
get(int)
,
add(int,
E), remove(int),
Object)
,
remove(int)
,
addAll(int, Collection)
and
removeRange(int, int)
methods all delegate to the corresponding methods on the backing abstract list, after bounds-checking the index and adjusting for the offset. The
addAll(Collection c)
method merely returns
addAll(size,
c).
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. The
iterator
method merely returns
listIterator(),
listIterator()
,
and the
size
method merely returns the subclass's
size
field.
All methods first check to see if the actual modCount of the backing list is equal to its expected value, and throw a ConcurrentModificationException if it is not.
public boolean equals(Object o)
e1.equals(e2)).)
This implementation first checks if the specified object is this list. If so, it returns
true;
true
;
if not, it checks if the specified object is a list. If not, it returns
false;
false
;
if so, it iterates over both lists, comparing corresponding pairs of elements. If any comparison returns
false,
false
,
this method returns
false.
false
.
If either iterator runs out of elements before the other it returns
false
(as the lists are of unequal length); otherwise it returns
true
when the iterations complete.
public int hashCode()
This implementation uses exactly the code that is used to define the list hash function in the documentation for the List.hashCode() method.
protected void removeRange(int fromIndex,
int toIndex)
fromIndex,
toIndex,
toIndex==fromIndex,
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.
This implementation gets a list iterator positioned before
fromIndex,
fromIndex
,
and repeatedly calls
ListIterator.next
followed by
ListIterator.remove
until the entire range has been removed.
Note: if
ListIterator.remove
requires linear time, this implementation requires quadratic time.