AbstractListpublic abstract class AbstractList extends AbstractCollection implements List| 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 the "random access"
methods: get(int index), set(int index, Object element),
set(int index, 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. |
| Fields Summary |
|---|
| protected transient int | modCountThe 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, 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. |
| Constructors Summary |
|---|
protected AbstractList()Sole constructor. (For invocation by subclass constructors, typically
implicit.)
|
| Methods Summary |
|---|
| public boolean | add(E o)Appends the specified element to the end of this List (optional
operation).
This implementation calls add(size(), o).
Note that this implementation throws an
UnsupportedOperationException unless add(int, Object)
is overridden.
add(size(), o);
return true;
| | 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).
This implementation always throws an UnsupportedOperationException.
throw new UnsupportedOperationException();
| | public boolean | addAll(int index, java.util.Collection 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 the
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.)
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.
boolean modified = false;
Iterator<? extends E> e = c.iterator();
while (e.hasNext()) {
add(index++, e.next());
modified = true;
}
return modified;
| | public void | clear()Removes all of the elements from this collection (optional operation).
The collection will be empty after this call returns (unless it throws
an exception).
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.
removeRange(0, size());
| | public boolean | equals(java.lang.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 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.
if (o == this)
return true;
if (!(o instanceof List))
return false;
ListIterator<E> e1 = listIterator();
ListIterator e2 = ((List) o).listIterator();
while(e1.hasNext() && e2.hasNext()) {
E o1 = e1.next();
Object o2 = e2.next();
if (!(o1==null ? o2==null : o1.equals(o2)))
return false;
}
return !(e1.hasNext() || e2.hasNext());
| | public abstract E | get(int index)Returns the element at the specified position in this list.
| | public int | hashCode()Returns the hash code value for this list.
This implementation uses exactly the code that is used to define the
list hash function in the documentation for the List.hashCode
method.
int hashCode = 1;
Iterator<E> i = iterator();
while (i.hasNext()) {
E obj = i.next();
hashCode = 31*hashCode + (obj==null ? 0 : obj.hashCode());
}
return hashCode;
| | public int | indexOf(java.lang.Object o)Returns the index in this list of the first occurence of the specified
element, or -1 if the 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.
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.
ListIterator<E> e = listIterator();
if (o==null) {
while (e.hasNext())
if (e.next()==null)
return e.previousIndex();
} else {
while (e.hasNext())
if (o.equals(e.next()))
return e.previousIndex();
}
return -1;
| | public java.util.Iterator | iterator()Returns an iterator over the elements in this list in proper
sequence.
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.
return new Itr();
| | public int | lastIndexOf(java.lang.Object o)Returns the index in this list of the last occurence of the specified
element, or -1 if the 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.
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.
ListIterator<E> e = listIterator(size());
if (o==null) {
while (e.hasPrevious())
if (e.previous()==null)
return e.nextIndex();
} else {
while (e.hasPrevious())
if (o.equals(e.previous()))
return e.nextIndex();
}
return -1;
| | public java.util.ListIterator | listIterator()Returns an iterator of the elements in this list (in proper sequence).
This implementation returns listIterator(0).
return listIterator(0);
| | public java.util.ListIterator | listIterator(int index)Returns a list iterator of 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 the next method. An initial call to
the previous method 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, 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.
if (index<0 || index>size())
throw new IndexOutOfBoundsException("Index: "+index);
return new ListItr(index);
| | 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.
This implementation always throws an
UnsupportedOperationException.
throw new UnsupportedOperationException();
| | 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 ArrayList 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.
ListIterator<E> it = listIterator(fromIndex);
for (int i=0, n=toIndex-fromIndex; i<n; i++) {
it.next();
it.remove();
}
| | public E | set(int index, E element)Replaces the element at the specified position in this list with the
specified element (optional operation).
This implementation always throws an
UnsupportedOperationException.
throw new UnsupportedOperationException();
| | public java.util.List | subList(int fromIndex, int toIndex)Returns a view of the portion of this list between 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 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 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 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.
return (this instanceof RandomAccess ?
new RandomAccessSubList<E>(this, fromIndex, toIndex) :
new SubList<E>(this, fromIndex, toIndex));
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