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 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 index) and size() methods.
To implement a modifiable list, the programmer must additionally override the set(int index, Object element) method (which otherwise throws an UnsupportedOperationException . If the list is variable-size the programmer must additionally override the add(int index, Object element) and remove(int index) 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 index)
,
set(int index,
E
Object
element)
,
add(int
set(int
index,
E
Object
element)
,
add(int index, Object element)
and
remove(int index)
.
The documentation for each non-abstract 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 .
| 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
Appends the specified element to the end of this
list
|
| 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
|
| 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
Returns the index
occurrence
element in this list,
this
the
|
| Iterator < E > |
iterator
() Returns an iterator over the elements in this list in proper sequence. |
| int |
lastIndexOf
(
Object
Returns the index
occurrence
element in this list,
this
the
|
| ListIterator < E |
listIterator
() Returns
a list
over
|
| 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
|
| 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 , inclusive, and toIndex , exclusive. |
| 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 , 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, 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, Object) 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.
| Constructor Detail |
|---|
protected AbstractList()
| Method Detail |
|---|
public boolean add(Eo)
list
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)
o)
.
Note that this implementation throws an UnsupportedOperationException unless add(int, Object) is overridden.
e
list
(as specified by
Collection.add(E)
)
operation
list
list
NullPointerException
- if the specified element is null and this list does not permit null elements
if
some
property
list
public abstract E get(int index)
the
element to
return
list
)
public E set(int index,
E element)
This implementation always throws an UnsupportedOperationException .
the
element to
replace
position
position
operation
list
list
NullPointerException
- if the specified element is null and this list does not permit null elements
property
list
)
public void add(int index,
E element)
This implementation always throws an
UnsupportedOperationException
.
UnsupportedOperationException.
inserted
inserted
operation
list
list
NullPointerException
- if the specified element is null and this list does not permit null elements
property
list
if the
index is out of range (
index < 0 || index > size()
)
public E remove(int index)
This implementation always throws an UnsupportedOperationException .
be removed
position
operation
list
)
public int indexOf(Object o)
occurrence
element in this list,
this
the
(o==null ? get(i)==null : o.equals(get(i)))
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.
for
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
- 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)
public int lastIndexOf(Object o)
occurrence
element in this list,
this
the
(o==null ? get(i)==null : o.equals(get(i)))
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.
for
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
- 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)
public void clear()
list
list
returns.
This implementation calls removeRange(0, size()) .
Note that this implementation throws an UnsupportedOperationException unless remove(int index) or removeRange(int fromIndex, int toIndex) is overridden.
operation
list
public boolean addAll(int index,
Collection<? extends E> c)
this
undefined
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, Object) . Many implementations will override this method for efficiency.
Note that this implementation throws an UnsupportedOperationException unless add(int, Object) is overridden.
collection
collection containing
elements to be
added to
list
call
operation
list
list
NullPointerException
- if the specified collection contains one or more null elements and this list does not permit null elements, or if the specified collection is null
if
some
property of
list
if the
index
is
out of range (
index < 0 || index > size()
)
public Iterator<E> iterator()
This implementation returns a straightforward implementation of the iterator interface, relying on the backing list's 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.
sequence
public ListIterator<E> listIterator()
a list
over
This implementation returns listIterator(0) .
a list
over
sequence)
public ListIterator<E> listIterator(int index)
this
next
.
previous
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) , set(int, Object) , add(int, Object) and remove(int) methods.
Note that the list iterator returned by this implementation will throw an UnsupportedOperationException in response to its remove , set and add methods unless the list's remove(int) , set(int, Object) , and add(int, 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.
method)
this list
)
public List<E> subList(int fromIndex,
int toIndex)
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
operating on
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
the
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 . 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 . If this list implements RandomAccess the returned list will be an instance of the subclass that implements RandomAccess .
The subclass's set(int, Object) , get(int) , add(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) .
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() , 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.
subList
subList
list
if the
endpoint indices
are
out of order
(fromIndex > toIndex)
public boolean equals(Object o)
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 returns false ; if so, it iterates over both lists, comparing corresponding pairs of elements. If any comparison returns false , this method returns 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.
list
list
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()
List.hashCode
method.
list
protected void removeRange(int fromIndex,
int toIndex)
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 , 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.
removed
removed