To answer specifically: note that
java.util.LinkedList defines a doubly-linked list.
The list has two member variables
last that reference ("point at") the first and last nodes. List nodes are of type
Entry<T>, where T is the type of the objects you are inserting.
Each list node or
Entry thus contains:
T data : the actual item (object) inserted
Entry<T> next : a reference to ("pointing at") the next node (null if last)
Entry<T> previous : a reference to ("pointing at") the previous node (null if first)
For example, list (A,B,C,D) is represented as follows:
/ \ -> / \ -> / \ -> / \
| A | | B | | C | | D |
\ / <- \ / <- \ / <- \ /