public abstract class AbstractList<E> extends AbstractCollection<E> implements List<E>
List interface to minimize the
effort required to implement this interface backed by a "random access" data store (such as an
array).
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.
| Modifier and Type | Field and Description |
|---|---|
protected int |
modCount
The number of times this list has been structurally modified.
|
| Modifier | Constructor and Description |
|---|---|
protected |
AbstractList()
Sole constructor.
|
| 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(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 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).
|
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.
|
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, 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 AbstractList()
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).
Note that this implementation throws an UnsupportedOperationException unless
add(int, E) is overridden.
add in interface Collection<E>add in interface List<E>add in class AbstractCollection<E>e - element to be appended to this listtrue (as specified by Collection.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 listpublic void add(int index,
E element)
This implementation always throws an UnsupportedOperationException.
add in interface List<E>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())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). Many implementations will override this method for
efficiency.
Note that this implementation throws an UnsupportedOperationException unless
add(int, E) is overridden.
addAll in interface List<E>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())public void clear()
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.
clear in interface Collection<E>clear in interface List<E>clear in class AbstractCollection<E>UnsupportedOperationException - if the clear operation is not supported by this listpublic boolean equals(@Nullable Object o)
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 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.
equals in interface Collection<E>equals in interface List<E>equals in class Objecto - the object to be compared for equality with this listtrue if the specified object is equal to this listObject.hashCode(),
HashMappublic abstract E get(int index)
get in interface List<E>index - index of the element to returnIndexOutOfBoundsException - if the index is out of range (index < 0 || index >= size())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.
hashCode in interface Collection<E>hashCode in interface List<E>hashCode in class ObjectObject.equals(java.lang.Object),
System.identityHashCode(java.lang.Object)public int indexOf(Object o)
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.
indexOf in interface List<E>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)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.
public int lastIndexOf(Object o)
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.
lastIndexOf in interface List<E>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)public ListIterator<E> listIterator()
This implementation returns listIterator(0).
listIterator in interface List<E>listIterator(int)public ListIterator<E> listIterator(int index)
next. An initial call to
previous would return the element with the specified index minus
one.
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, E), add(int, E) 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, E), and
add(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.
listIterator in interface List<E>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())public E remove(int index)
This implementation always throws an UnsupportedOperationException.
remove in interface List<E>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())protected void removeRange(int fromIndex,
int toIndex)
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.
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.
fromIndex - index of first element to be removedtoIndex - index after last element to be removedpublic E set(int index, E element)
This implementation always throws an UnsupportedOperationException.
set in interface List<E>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())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. 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, E), get(int), add(int, E), 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 in interface List<E>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)