Collections - The Java Programming Language - page 858

21.6. List
The List<E> interface extends Collection<E> to define a collection whose
elements have a defined ordereach element exists in a particular position
in the collection, indexed from 0 to list.size()-1 . Or, in other words, a
List defines a sequence of elements. This requires a refinement of the
contracts of several methods inherited from Collection : when you add an
element, it is placed at the end of the list; When you remove the n th ele-
ment from the list, the element that was after it is shifted over, becoming
the new n th element; and the toArray methods fill in the array in the list's
order.
List also adds several methods that make sense in an ordered collection:
public E get(int index)
Returns the index th entry in the list.
public E set(int index, E elem)
Sets the index th entry in the list to elem , replacing the previous
element and returning it. (Optional)
public void add(int index, E elem)
Adds the entry elem to the list at the index th position, shifting
every element farther in the list down one position. (Optional)
public E remove(int index)
Removes and returns the index th entry in the list, shifting every
element farther in the list up one position. (Optional)
public int indexOf(Object elem)