Lab 3: Credit Cards

Steven K. Andrianoff

Robert Harlan

David Levine

Computer Science Department

St. Bonaventure University

Copyright,  2003

Due:    Friday, February 6

Objective:

This lab provides a CreditCard class and requires students to create CreditCard objects and exercise the CreditCard methods.  Students will test the behavior of the CreditCard methods without having access to the source code for the CreditCard class.

Background:

For this lab you will be provided with a CreditCard class.  You will not have access to the source code (Java code) for the class. However the class has the following methods:

• A constructor that takes no arguments
• A second constructor that takes a single integer (numeric) argument
• A pay method with the signature:
             public void pay(int amount)
• A charge method with the signature:
             public void charge(int amount)
• A limit method with the signature
             public int limit()
• A totalDue method with the signature
             public int totalDue()
• A minimumDue method with the signature
             public int minimumDue()

You can probably infer the behavior of the methods from their names.  Your task in the lab is to exercise the methods to precisely determine their behavior.

1. Launch the Eclipse development environment. Create a new project named  Lab3. 
   
   Have your lab instructor help you add the jar file Lab3.jar to your project.
   
   Create a class named CardTester.  As in Lab 2, select File / New / Class.  Make sure the source folder is Lab3. Name the class CardTester. Make sure the Modifier public is selected and the public static void main(String[] args) checkbox is checked. Click Finish. The editor window should open a file named CardTester.java with a skeleton of the CardTester class with a main method in it.
   
   All the coding in the succeeding steps involve writing statements in the main method of the CardTester class.  Begin by modifying the comments to include your names and the date.  For a description just say that this is a program to test the CreditCard class.



2. Add statements to the main method to declare then create a CreditCard object. 
   
   What is the initial limit of the card?  Write statements to determine the limit and display it. 
   

   (For the purposes of this lab, use System.out.println() for displaying information in the console window.  Also, label any displayed information, for example,
         System.out.println(“Limit: “ + amt);  )
   
   How much is owed initially?  What is the minimum payment initially?  Record your results and provide a copy of the statements you used to find and display this information.



3. There is a second constructor for the CreditCard class that takes a single integer argument.  Create a card using this constructor and determine the initial limit, amount owed, and minimum payment.  Describe how this constructor is different from the constructor that takes no arguments.  Record your results and provide a copy of the statements you used to find and display this information.
   


4. Modify the program from Step 3 by adding statements to make a charge on the card after it is created.    How does the charge affect the limit?  How does it affect the amount owed?  How does it affect the minimum payment?  Add statements to perform these tests.  Record your results and provide a copy of the statements you used to find and display this information.



5. Further modify the program from Step 4 to make a payment on the card after the charge.  How does the payment affect the limit?  How does it affect the amount owed?  How does it affect the minimum payment?  Add statements to perform these tests.  Record your results and provide a copy of the statements you used to find and display this information.



6. Describe how the minimum payment is calculated.  Be careful, there may be special cases.  Provide a copy of the statements you used to determine how the minimum payment is calculated.  Describe the results of your tests.
   


7. Can you find charges that cause errors to be displayed?  (Hint: there are two types of charges that will result in error messages.)  Provide a copy of the statements that resulted in errors and record the error messages.
   


8. Comment out all the statements except the statements to create the card and statements to make a single charge.  Display the current limit, amount owed, and minimum payment after this charge.  Now experiment with various payments.  What happens to the limit, the amount owed, and the minimum payment when a full payment is made?  What happens to these when a partial payment is made?  Provide a copy of the statements you used to answer these questions and the results you obtained.
    


9. Can you find payments that cause errors to be displayed?  (Hint: there three types of payments that will result in error messages.)  Provide a copy of the statements that resulted in errors and record the error messages.



10. Make sure all of your tests are still in the main method even though most of them may be commented out.  Print a copy of the file CardTester.java and hand it in with your lab write-up.

Extra Credit: Run similar tests on another class named ImprovedCreditCard.  Create a new class called ImprovedCardTester with a main method in it. 

The ImprovedCreditCard class has the same set of methods as the CreditCard class however one or more of the methods behave differently.  Write statements to test this new class.  What methods behave differently?  Carefully describe the different behavior based on tests you write.  Provide a copy of the statements you used to investigate the different behavior and how the behavior is different.

Make sure the comments in the file ImprovedCardTester.java are appropriate then print a copy of the file ImprovedCardTester.java and hand it in with your lab write-up.

Hand in:

The write-up you hand in for this lab should include:
-    answers to questions in Steps 2-9
-    the record of results and a copy of statements used as requested in Steps 2-9
-    a printout of the program (source code) requested in Steps 10
-    if you do the Extra Credit, answer the questions, record the results of your tests, include a copy of the statements used, and provide a printout of the source code

 

Help Policy:

Help Policy in Effect for This Assignment:  Group Project with Limited Collaboration

In particular, you may discuss the assignment and concepts related to the assignment with the following persons, in addition to an instructor in this course: any member of your group; any St. Bonaventure Computer Science instructor; and any student enrolled in CS 131. 

You may use the following materials produced by other students:  materials produced by members of your group.