CSSE 221: Fundamentals of Software Development Honors

BigRational

Objectives

Create a class to store and process a rational number of arbitrary precision, e.g.

        74939393930003456 / 83838384550230300266666629999

Using the Java API

Implementing interfaces (writing to a specification)

Implementing by using documented stubs

Unit testing

The Object class and when its methods should be overridden

Tasks

Background research: Answer the questions on today's quiz.
- Open the Java API.
- Navigate to the BigInteger class. Why is it useful? Why not just use ints?
- Note that BigInteger implements Comparable.
- Navigate to the Comparable interface and figure out what it is all about. What method(s) must a class implement if it implements Comparable?
- Hmm. Does BigInteger have a compareTo() method? (Navigate back there to check.)
- Why must BigInteger have a compareTo() method?
- Review this documentation for the ArithmeticObject interface. This interface is not part of the Java library—we created it.
Checkout the BigRational project in Eclipse. (See JavaEyes if you forgot how.)
Examine the BigRational class. Do the TODO items in order. Commit your code to SVN often, say after you get each method to work. That way you’ll have a backup of each phase of your work. Some special notes:
- TODO 2: just write implements Comparable<BigRational> after the name of the class. This will stub in the methods that are part of the interface. (Stubs are just empty method bodies.)
- Interfaces do not specify constructors, but I have stubbed in two for you. Implement them first. Interfaces also do not specify fields, so you’ll have to decide what field(s) to use.
- Note that since we are dealing with fractions, we should give all answers in lowest terms (reduced). Hint: A careful perusal of the BigInteger class should reveal a method that will save you lots of time here.
- TODO 6 and 7: Implement the stubbed in equals() and toString() methods. Note: until you write equals(), it always returns false. Your implementation of toString() should be simple—just format in the form a/b—but be sure to format to the reduced form of the fraction. Examples:
  - 2/3 (rather than 4/6)
  - 4 (rather than 4/1)
  - -6/5 (negative in numerator, rather than 6/-5)
  - 1/2 (no double negative, rather than -1/-2)
  - 0 (rather than 0/3)
- TODO 6 and 8: Create unit tests for toString and each Arithmetic method. We'll discuss this in class in Thursday. You will be graded on how well you choose your test cases.
- TODO 8: Note that BigRational is an immutable class. Each math method should return a brand new object, leaving the operands untouched.
- The divide method specifies that it throws an “ArithmeticException” on division by zero. We'll study exceptions on Thursday.

In all your code:

Write appropriate comments:
- Javadoc comments for public fields and methods.
- Explanations of anything else that is not obvious.
Give self-documenting variable and method names:
- Use name completion in Eclipse, Ctrl-Space, to keep typing cost low and readability high.
Use Ctrl-Shift-F in Eclipse to format your code.
Take care of all auto-generated TODO's.
- Then delete the TODO comment.
Correct ALL compiler warnings.
- Quick Fix is your friend!

Here is the grading rubric for this assignment.

Turn-in Instructions

Turn in your programming work by committing it to your SVN repository for this project. Make sure that your unit tests are committed as well!