CS U370 Assignment #4
Section:  Clinger
Assigned:  Friday, 19 October 2006
Due:  Friday, 3 November 2006

The purpose of this assignment is:

 * To translate an algebraic specification of an immutable abstract
   data type into executable Java code
 * To review the java.util.Comparator interface
 * To see how simple selection and sorting algorithms can
   be specified algebraically
 * To introduce a non-trivial example that illustrates
   and motivates future topics

You will complete an implementation in Java of the Report ADT 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 4

and a body that consists of nothing but your Report.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 your following the procedure above
for submitting your work.  Late assignments may be discounted, and very 
late assignments may be discarded.

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Specification of the Report ADT.

Report is an immutable abstract data type.  In our implementation
language, Java, it corresponds to the project.Report class, which
is specified below.

The Report class shall be implemented in Java, and will be tested using 
Sun's Java 2 Runtime Environment, Standard Edition, version 5.0. The code 
for this implementation will be in the project package, and shall define 
a public class named Report, which provides the following public methods, 
which are specified below.

Signature and Java syntax:

// Basic creators, to be located within the Report class.

public static Report empty();
public static Report adjoin(Report, Issue);

// Derived creators, to be located within the Report class.

public static Report select(Report, Comparator<Issue>, Issue);
public static Report sort(Report, Comparator<Issue>);
public static Report insert(Report, Comparator<Issue>, Issue);

// Accessors

public static int length(Report);
public static Issue first(Report);
public static Issue last(Report);
public static Report withoutFirst(Report);
public static Report withoutLast(Report);

// Canonical Methods

public String toString();


Specification of behavior:

Report.select(Report.empty(), comp, iss0) = Report.empty()

Report.select(Report.adjoin(r, issue), comp, iss0)
    = Report.adjoin(Report.select(r, comp, iss0), issue)
                if comp.compare(issue, iss0) = 0

Report.select(Report.adjoin(r, issue), comp, iss0)
    = Report.select(r, comp, iss0)
                if comp.compare(issue, iss0) != 0

Report.sort(Report.empty(), comp) = Report.empty()

Report.sort(Report.adjoin(r, issue), comp)
    = Report.insert(Report.sort(r, comp), comp, issue)

Report.insert(Report.empty(), comp, iss0)
    = Report.adjoin(Report.empty(), iss0)

Report.insert(Report.adjoin(r, issue), comp, iss0)
    = Report.adjoin(Report.adjoin(r, issue), iss0)
                if comp.compare(issue, iss0) <= 0

Report.insert(Report.adjoin(r, issue), comp, iss0)
    = Report.adjoin(Report.insert(r, comp, iss0), issue)
                if comp.compare(issue, iss0) > 0

Report.length(Report.empty()) = 0

Report.length(Report.adjoin(r, issue)) = Report.length(r) + 1

Report.first(Report.adjoin(r, issue))
    = issue     if Report.length(r) = 0

Report.first(Report.adjoin(r, issue))
    = Report.first(r)
                if Report.length(r) > 0

Report.last(Report.adjoin(r, issue)) = issue

Report.withoutFirst(Report.adjoin(r, issue))
    = Report.empty()
                if Report.length(r) = 0

Report.withoutFirst(Report.adjoin(r, issue))
    = Report.adjoin(Report.withoutFirst(r), issue)
                if Report.length(r) > 0

Report.withoutLast(Report.adjoin(r, issue)) = r

Report.empty().toString() = "Report: empty"

Report.adjoin(r, issue).toString()
    = issue.toString()
                if Report.length(r) = 0

Report.adjoin(r, issue).toString()
    = r.toString() + "\n" + issue.toString()
                if Report.length(r) > 0


Note 1: The comparator argument to the select and sort methods
is not necessarily consistent with equals.

Note 2: The compare method of the comparator argument to the
select and sort methods must not have any side effects.

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