Your instructor may assign one or more of the following problems. Don’t feel that you must do all the problems; for the homeworks, you are only required to do those that are explicitly assigned via Moodle.

Submit your work as you did for lab01.

1. BIG PICTURE: Write a graphical user interface to calculate a monthly loan payment.

   Details:

   • You should model a loan using a class with the following instance variables:
     • length of loan (in years)
     • initial amount of loan (in dollars)
     • annual interest percentage
     This class should be in a module called loan and should:
     • Maintain invariants so that all instance variables are positive
     • Provide mutators to change each instance variable
     • Provide a method that computes the monthly payment for the loan according to the following:

       Let n = years * 12
       Let i = annualInterest / 100  / 12
       Then D = {[(1 + i)^n] - 1} / [i (1 + i)^n]
       and monthlyPayment = loan / D

       NOTE: The above is pseudocode, not something that can be copied into your solution directly.

   • The graphical user interface should be in a module called loan_calculator and use pairs of labels and entries to indicate and allow the user to enter each of:
     • Loan amount
     • Years
     • Annual Interest Percentage
   • Finally, there should be a button that lets the user calculate their monthly payment using the values in the entries, and then displays this information on the GUI.
2. 

   Create a temperature class whose constructor receives a Fahrenheit temperature and implements an accessor method that computes and returns the equivalent degrees in Celsius. No temperature should be below absolute zero. Let the default temperature be 0.0 degrees Fahrenheit.

   Create unit tests for the temperature class, including tests for the correctness of the temperature conversion and for the exceptions that can be raised.

   Create a GUI, similar to the fraction simplification example, that allows a user to enter a Fahrenheit temperature value and convert the value to Celsius. Send all welcome and error messages to a message panel at the bottom of the interface. See the example on the right.

Checking In

Submit all appropriate files for grading, including code files, screen captures, supplemental files (e.g., image files), and text files. We will grade this exercise according to the following criteria:

• Correctness:
  • 40% - Model and associated calculation is correct (e.g. loan class). If unit tests are required, they must be implemented properly.
  • 40% - Graphical User Interface works correctly
• Understandability:
  • 5% - Code Documentation - Separate the logical blocks of your program with useful comments and white space.
  • 5% - Header Documentation - Document the code’s basic purpose, authors and assignment number.
• Usability:
  • 10% - GUI is intuitive