AbstractListpublic abstract class AbstractList extends AbstractCollection implements List| This class provides a skeletal implementation of the {@link 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), {@link 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 {@link #get(int)} and
{@link List#size() size()} methods.
To implement a modifiable list, the programmer must additionally
override the {@link #set(int, Object) set(int, E)} method (which otherwise
throws an {@code UnsupportedOperationException}). If the list is
variable-size the programmer must additionally override the
{@link #add(int, Object) add(int, E)} and {@link #remove(int)} methods.
The programmer should generally provide a void (no argument) and collection
constructor, as per the recommendation in the {@link 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:
{@link #get(int)},
{@link #set(int, Object) set(int, E)},
{@link #add(int, Object) add(int, E)} and
{@link #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. |
| 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 {@code iterator} and {@code listIterator} methods.
If the value of this field changes unexpectedly, the iterator (or list
iterator) will throw a {@code ConcurrentModificationException} in
response to the {@code next}, {@code remove}, {@code previous},
{@code set} or {@code 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 {@code add(int, E)} and
{@code remove(int)} methods (and any other methods that it overrides
that result in structural modifications to the list). A single call to
{@code add(int, E)} or {@code remove(int)} must add no more than
one to this field, or the iterators (and list iterators) will throw
bogus {@code 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 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.
This implementation calls {@code add(size(), e)}.
Note that this implementation throws an
{@code UnsupportedOperationException} unless
{@link #add(int, Object) add(int, E)} is overridden.
add(size(), e);
return true;
| | public void | add(int index, E element){@inheritDoc}
This implementation always throws an
{@code UnsupportedOperationException}.
throw new UnsupportedOperationException();
| | public boolean | addAll(int index, java.util.Collection c){@inheritDoc}
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 {@code add(int, E)}.
Many implementations will override this method for efficiency.
Note that this implementation throws an
{@code UnsupportedOperationException} unless
{@link #add(int, Object) add(int, E)} 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 list (optional operation).
The list will be empty after this call returns.
This implementation calls {@code removeRange(0, size())}.
Note that this implementation throws an
{@code UnsupportedOperationException} unless {@code remove(int
index)} or {@code 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
{@code 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 {@code e1} and
{@code e2} are equal if {@code (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 {@code true}; if not, it checks if the
specified object is a list. If not, it returns {@code false}; if so,
it iterates over both lists, comparing corresponding pairs of elements.
If any comparison returns {@code false}, this method returns
{@code false}. If either iterator runs out of elements before the
other it returns {@code false} (as the lists are of unequal length);
otherwise it returns {@code 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){@inheritDoc}
| | 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 {@link 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){@inheritDoc}
This implementation first gets a list iterator (with
{@code 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 {@code size()},
{@code get(int)}, and {@code remove(int)} methods.
Note that the iterator returned by this method will throw an
{@code UnsupportedOperationException} in response to its
{@code remove} method unless the list's {@code 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) {@code modCount} field.
return new Itr();
| | public int | lastIndexOf(java.lang.Object o){@inheritDoc}
This implementation first gets a list iterator that points to the end
of the list (with {@code 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(){@inheritDoc}
This implementation returns {@code listIterator(0)}.
return listIterator(0);
| | public java.util.ListIterator | listIterator(int index){@inheritDoc}
This implementation returns a straightforward implementation of the
{@code ListIterator} interface that extends the implementation of the
{@code Iterator} interface returned by the {@code iterator()} method.
The {@code ListIterator} implementation relies on the backing list's
{@code get(int)}, {@code set(int, E)}, {@code add(int, E)}
and {@code remove(int)} methods.
Note that the list iterator returned by this implementation will
throw an {@code UnsupportedOperationException} in response to its
{@code remove}, {@code set} and {@code add} methods unless the
list's {@code remove(int)}, {@code set(int, E)}, and
{@code 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) {@code modCount} field.
if (index<0 || index>size())
throw new IndexOutOfBoundsException("Index: "+index);
return new ListItr(index);
| | public E | remove(int index){@inheritDoc}
This implementation always throws an
{@code UnsupportedOperationException}.
throw new UnsupportedOperationException();
| | protected void | removeRange(int fromIndex, int toIndex)Removes from this list all of the elements whose index is between
{@code fromIndex}, inclusive, and {@code toIndex}, exclusive.
Shifts any succeeding elements to the left (reduces their index).
This call shortens the ArrayList by {@code (toIndex - fromIndex)}
elements. (If {@code toIndex==fromIndex}, this operation has no
effect.)
This method is called by the {@code 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 {@code clear} operation on this list
and its subLists.
This implementation gets a list iterator positioned before
{@code fromIndex}, and repeatedly calls {@code ListIterator.next}
followed by {@code ListIterator.remove} until the entire range has
been removed. Note: if {@code 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){@inheritDoc}
This implementation always throws an
{@code UnsupportedOperationException}.
throw new UnsupportedOperationException();
| | public java.util.List | subList(int fromIndex, int toIndex){@inheritDoc}
This implementation returns a list that subclasses
{@code 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
{@code modCount} value of the backing list. There are two variants
of the subclass, one of which implements {@code RandomAccess}.
If this list implements {@code RandomAccess} the returned list will
be an instance of the subclass that implements {@code RandomAccess}.
The subclass's {@code set(int, E)}, {@code get(int)},
{@code add(int, E)}, {@code remove(int)}, {@code addAll(int,
Collection)} and {@code 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
{@code addAll(Collection c)} method merely returns {@code addAll(size,
c)}.
The {@code 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 {@code iterator} method
merely returns {@code listIterator()}, and the {@code size} method
merely returns the subclass's {@code size} field.
All methods first check to see if the actual {@code modCount} of
the backing list is equal to its expected value, and throw a
{@code 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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