CS U370 Assignment #3
Section:  Clinger
Assigned:  Tuesday, 20 January 2009
Corrected: Sunday, 25 January 2009 (see ! in column 79)
Due: Tuesday, 27 January 2009

The purpose of this assignment is:

 * To use the standard recipe
 * To continue our study of abstraction-based software design by
   implementing a third algebraic specification
 * To continue our review of static methods
 * To give a third example of factory methods for creating new objects

You will complete an implementation in Java of the Dependencies
ADT that is specified below.  Collaboration between students is
forbidden on this assignment.  You are responsible for keeping your
code hidden from all other students.  Turn in your work on this
assignment before 10 pm on the due date by sending electronic mail
to:  will@ccs.neu.edu

with subject
    CSU370 assignment 3

and a body that consists of nothing but your Dependencies.java file.
That file should begin with a block comment that lists
    1.  Your name, as you want the instructor to write it.
    2.  Your email address.
    3.  Any remarks that you wish to make to the instructor.

Part of your grade will depend on the quality and correctness of your
code, part will depend on the readability of your code (comments and
indentation), and part will depend on how well you follow the procedure
above for submitting your work.  Late assignments may be discounted,
and very late assignments may be discarded.

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Your assignment is to write the code for a single file,
Dependencies.java, that implements the specification below.
For this assignment, an inadequate test program is provided
at /course/csu370wc/Assignments/A3/TestDependencies.java .
You will need to supplement that test program with your own
tests.

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Specification of the Dependencies ADT.

Like the Refreshable and Dependency abstract data types, the
Dependencies abstract data type is immutable.

The Dependencies ADT shall be implemented in Java, and will be tested
using Sun's Java 2 Runtime Environment, Standard Edition, version 1.6.0.
The code for this implementation will be in the default package, and
shall define a public class named Dependencies.  That class shall
provide the following public static methods:

Signature:

    Dependencies.none   :                            ->  Dependencies
    Dependencies.adjoin : Dependency * Dependencies  ->  Dependencies
    Dependencies.absent : Dependencies               ->  boolean
    Dependencies.first  : Dependencies               ->  Dependency
    Dependencies.rest   : Dependencies               ->  Dependencies         !
    Dependencies.okay   : Dependencies               ->  boolean

    Dependencies.absent (Dependencies.none()) = true

    Dependencies.absent (Dependencies.adjoin (d, s)) = false

    Dependencies.first (Dependencies.adjoin (d, s)) = d

    Dependencies.rest (Dependencies.adjoin (d, s)) = s

    Dependencies.okay (Dependencies.none()) = true

    Dependencies.okay (Dependencies.adjoin (d, s))
        = Dependency.isOkay(d) && Dependencies.okay(s)

Values of the Dependencies ADT shall also implement the public
dynamic methods equals(Object) and hashCode() such that

    If v1 and v2 are values of the Dependencies ADT, then

        v1.equals(v2) if and only if

            (Dependencies.absent(v1) and Dependencies.absent(v2))
            or
            ((not Dependencies.absent(v1))
             and
             (not Dependencies.absent(v2))
             and
             Dependencies.first(v1).equals(Dependencies.first(v2))
             and
             Dendencies.rest(v1).equals(Dependencies.rest(v2)))

    If v1 is a value of the Dependencies ADT, but x is not, then

        v1.equals(x) returns false.

    If v1 and v2 are values of the Dependencies ADT, and

        v1.equals(v2)

    then v1.hashCode() == v2.hashCode().

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