600.321/421, Object Oriented Systems
Smalltalk Assignment 1
Due: Friday Sep 25, 5PM

Code the following Grade class in a new class category named precisely Assignment1.

The built-in libraries of Smalltalk make very effective use of abstract classes. The Magnitude class is an abstract class which allows comparisons <, =, etc. Date, Time, Character are all subclasses of Magnitude.
Write a new magnitude class Grade, a subclass of Magnitude, which is a letter grade ranging from F- to A+.

• aGrade := Grade letter: $A modifier: #plus --makes a new A+ grade object. Modifiers can be #plus, #minus, or #none. (Recall that $A is the character constant A).
• aGrade := Grade new: 'A+' --a friendlier way to make a new A+ grade object.
• aGrade letter --the letter portion of the grade, $A here.
• aGrade modifier --the modifier portion, #plus here.
• aGrade increment -- bump the grade up by one full letter grade
• aGrade decrement -- bump the grade down by one full letter grade
• aGrade points --how many points the grade is worth, e.g. 4 for A, 3 for B, etc. The + adds .3 and a - subtracts .3. Also, an A+ is is an exception, its only worth 4.0, not 4.3.
• aGrade op anotherGrade where op is any comparison such as = < > ~=: compare grades in the standard way: B < B+, etc.
• Make sure all of the Magnitude protocol works (i.e. you have implemented everything that was the subclassResponsibility to implement), with the exception of hash (that really should be done, but we'll skip it for now).
• Write a printOn: aStream method so the grades get printed nicely in the workspace. (This is the method you have to write to get a nice print name for objects; the printString method discussed in class in fact calls printOn:). The aStream argument is a stream which is in fact the workspace buffer. All you need to know about streams for now is that
  aStream nextPutAll: 'A+'
  will for instance print out an A+ grade nicely. The Online Cookbook Ch. 25 tells it all Re: characters and strings so look there for useful methods.

Clarifications

1. A < A+ is true.
2. F- is worth -.3. This assignment is not asking that the bottom of the grade scale be implemented properly, Hopkins actually has no D-, F+, or F- grades. Assume it does.
3. Don't store the grade internally as a string since they are not so efficient.

Coding Style

• Be appropriate in your use of inheritance and overriding
• Put your methods in appropriately named protocols (look at other existing system classes for ideas on how to divide things into different protocol names)
• Make a class comment documenting your new class(write it by hitting the "comment" option on the class menu in the browser and typing; remember to execute accept to save your comment after you write it).

Submission Instructions

~scott/bin/submit Assignment1 Assignment1.st

You will need to ftp your files to hops first if you are working on some other machine.

Don't submit a .im file, they are too big! Use the file in/out tool instead.

You can check what files you submitted via

~scott/bin/query