COM 1205 Assignment #4.
Assigned:  Tuesday, 15 February 2000
Due:       Tuesday, 22 February 2000

Working in small teams that are assigned by the instructor,
you will design and code an implementation in Java of the
Histogram ADT that is specified below.  Your implementation
of this module will be used by other students in a future
assignment.

Collaboration between members of different teams is forbidden.
Each team is responsible for keeping its design and code hidden
from other teams.  Part of each team's grade will be determined
by how well the team hides its code, and part of the grade will
depend upon the quality of the implementation.  A team that
resolves the security issues and submits an implementation of
the specified module that the instructor considers acceptable
for use in a large software project will earn an A.

The instructor will designate one member of each team as the
lead programmer for that team.  The lead programmer is
responsible for submitting the team's work, and has the final
say concerning all design, coding, and testing decisions.  The
lead programmer is also responsible for dividing the team's work
among its members, and for scheduling team meetings at times
that are convenient for the team.  The other members of the team
are responsible for advising the lead programmer, for reviewing
the team's design, code, and tests, and for any other teamwork
that may be assigned by the lead programmer.

All members of a team will receive the same grade.  Every
student will serve as lead programmer for some assignment during
the term.  The teams will change at the whim of the instructor.

The lead programmer is responsible for turning in the team's
work before 4 pm on the due date by sending electronic mail to

    will@ccs.neu.edu

with subject

    assignment #4

and a body that consists of the following, in the order shown:

    1.  The names of the team members.
    2.  Any remarks that the lead programmer wishes to make to
        the instructor concerning the team's work.
    3.  A line consisting of exactly 50 hyphens.
    4.  The code for Histogram.java.

Late assignments may be discounted, and very late assignments
may be discarded.

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Specification of the Histogram module.

Histogram is an immutable abstract data type.  Its operations
shall have no visible side effects.  The Histogram ADT shall be
implemented in Java using JDK 1.2.  The code for this
implementation shall be in the statistics package, and shall
consist of a single file named Histogram.java.  This file shall
define a public class named Histogram that defines the
following public static methods, which are specified below.

Signature:

    newHistogram:  String                   ->  Histogram
    newHistogram:  StringBuffer             ->  Histogram
    length:        Histogram                ->  int
    frequency:     Histogram x char         ->  int
    frequency:     Histogram x char x char  ->  int
    mic:           Histogram x Histogram    ->  double

Restrictions:  The String and StringBuffer arguments to the
newHistogram operations shall not be null, and shall contain
only characters whose Unicode encoding is less than 128.

Algebraic specification:

Notation:

    s, s1, and s2 range over values of type String, and are not
    null.  b ranges over values of type StringBuffer, and is not
    null.  n, n1, n2, i, and j range over natural numbers of
    type int.  c, c1, and c2 range over values of type char
    whose Unicode encoding is less than 128.  h1 and h2 range
    over values of type Histogram.

    newHistogram (b)  =  newHistogram (b.toString())

    length (newHistogram (s))  =  s.length()

If n is the number of times that char c occurs within s, then
    frequency (newHistogram (s), c)  =  n

If n is the number of times that char c1 is followed by char c2
within s, then
    frequency (newHistogram (s), c1, c2)  =  n

If n1 = length (h1), n2 = length (h2), then
    mic (h1, h2)

            Sigma   (frequency (h1, c))  (frequency (h2, c))
              c
        =  -------------------------------------------------
                                  n1  n2