CS U370 Assignment #1
Section:  Clinger
Assigned:  Tuesday, 6 January 2009
Due: Tuesday, 13 January 2009

The purpose of this assignment is:

 * To review basic Java programming concepts, such as objects, methods, 
   variables, etc.
 * To introduce the Java API (application programming interface)
 * To acquaint you with the development system you choose to use
 * To learn the required procedure for submitting homework in this course
 * To begin our study of abstraction-based software design by providing
   an algebraic specification for the Refreshable ADT
 * To review static methods
 * To introduce the use of factory methods for creating new objects

You will complete an implementation in Java of the Refreshable
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 1

and a body that consists of nothing but your Refreshable.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, Refreshable.java, 
that implements the specification below.  For this first assignment,
a test program (/course/csu370wc/Assignments/A1/TestRefreshable.java)
is provided.  (In future assignments, you will be required to develop
your own test programs.)

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Specification of the Refreshable ADT.

The Refreshable 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 Refreshable.  That class shall
provide the following public static methods:

Signature:

    Refreshable.create : String * int -> Refreshable
    Refreshable.name   : Refreshable  -> String
    Refreshable.era    : Refreshable  -> long

    Refreshable.name (Refreshable.create (s, i)) = s

    Refreshable.era (Refreshable.create (s, i)) = i

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

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

        v1.equals(v2) if and only if
            Refreshable.name(v1).equals(Refreshable.name(v2))
        and Refreshable.era(v1) == (Refreshable.era(v2))

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

        v1.equals(x) returns false.

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

        v1.equals(v2)

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

Note: The second argument to Refreshable.create must be greater
than or equal to 0.  If this constraint is violated, then an
IllegalArgument exception should be thrown, as by the following
statement:

      throw new IllegalArgumentException("era < 0");

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