Data Structures and Algorithms in Java[1].pdf - Fulvio Frisone

In Code Fragment 6.6, we show a Java class DNode for the nodes of a doubly
linked list implementing the position ADT. This class is similar to class DNode
shown in Code Fragment 3.17, except that now our nodes store a generic element
instead of a character string. Note that the prev and next instance variables in the
DNode class below are private references to other DNode objects.
Code Fragment 6.6: Class DNode realizing a node
of a doubly linked list and implementing the Position
interface (ADT).
Given a position p in S, we can "unwrap" p to reveal the underlying node v. This is
accomplished by casting the position to a node. Once we have node v, we can, for
example, implement method prev(p) with v.getPrev (unless the node
returned by v.getPrev is the header, in which case we signal an error).
Therefore, positions in a doubly linked list implementation can be supported in an
object-oriented way without any additional time or space overhead.
Consider how we might implement the addAfter(p, e) method, for inserting
an element e after position p. Similar to the discussion in Section 3.3.1, we create a
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