TaxCalc

Quick Index

Objectives
Steps
Problem Statement
Hints
Solution
Test Code

Java interfaces (Java interfaces are known to be the best part of Java -- they simplify code)
Java packages
Writing Test Code

Take a shot at writing the program after viewing the problem statement
When desired, look at the hints
When desired, look at the solution

Code up a tax calculator.

The calculator should be able to compute taxes for any "taxable" object.

The model solution consists of a TaxCalculator and a Taxable type. Note that "Taxable" is a Java interface meaning it is an "idea". Thus, object users will have to replace it with "real" objects for use.

TaxCalculator

I am a simple calculator that calculates the tax for a Taxable type.

Note that my element must be a Taxable object type. I do not care if my ivar "element" is a car, house, etc. As long as it's a Taxable type, I'm happy.

I use OO encapsulation. I hide the unpleasant details of money math (rounding errors).

Taxable

I am the "idea" for something taxable.

Hint: Java interface = idea.

Note that we do not need to declare interface methods public. They are public by default.

Coding requirements:

Write the model class "TaxCalculator"
Write an interface "Taxable"
The interface Taxable only needs one method: "BigDecimal beforeTaxPrice()"
BigDecimal is used for accuracy
The class TaxCalculator should have an ivar named element of type "Taxable"
The class TaxCalculator should have a method "calculate" -- when it is called it akes the element and computes the "salesTax" and "afterTaxPrice" and sets the values into ivars
The class TaxCalculator should have one constructor that recieves two params -- the first is of type Taxable, and the second is a string representing the tax rate -- a hint is that the tax rate should be converted to a BigDecimal

Hints

Write test code as you code this model.

Solution

Here is code with explanations:

Test Code

Testing Problem Statement

Also reference the Association test write-up as needed.

Write code to test the model. If you get stumped, look at test code solution.

Test Code Solution

First, try to write test code yourself. Then review and compare the following for possible ideas.

Some helper class code to use on the tests:

The test code:

Here is support code that is needed for the test code.

Note that this support code is just one example of a minimal testing framework. Feel free to build your own.

Object Oriented Programming

TaxCalc

Top Search TOC