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

The node list ADT allows us to view an ordered collection of objects in terms of
their places, without worrying about the exact way those places are
represented.(See Figure 6.5.)
Figure 6.5: A node list. The positions in the current
order are p, q, r, and s.
There may at first seem to be redundancy in the above repertory of operations for
the node list ADT, since we can perform operation addFirst(e) with
addBefore(first(), e), and operation addLast(e) with
addAfter(getLast(), e). But these substitutions can only be done for a
nonempty list.
Note that an error condition occurs if a position passed as argument to one of the
list operations is invalid. Reasons for a position p to be invalid include:
• p = null
• p was previously deleted from the list
• p is a position of a different list
• p is the first position of the list and we call prev(p)
• p is the last position of the list and we call next(p).
We illustrate the operations of the node list ADT in the following example.
Example 6.3: We show below a series of operations for an initially empty list
node S. We use variables p 1 , p 2 , and so on, to denote different positions, and we
show the object currently stored at such a position in parentheses.
Operation
Output
S
addFirst(8)
329