Lab 04 Solution

For today’s lab you will be designing 2 classes, one of which will use the other. You will also be creating two testers using the “Class (Unit) Testing” approach outlined in lecture and the textbook for each of your two classes.




Part 1 (15 points)




Design a class Message that models an e-mail message. A message has a




recipient, a sender, and a message body representing the text of the message. Design the following methods:




A single constructor (no more) that takes in a sender and recipient.



A method append that appends a provided (parameter) line of text to the message body. Ensure that each line is terminated with a line break.
Override the public string toString method so that it returns a string



representation of the message as one long string like this:

“From: Harry Morgan\nTo: Rudolf Reindeer\n …(Message Body HERE)… \n”.




For this method, you must create and utilize two non-changing AND same across all object instances constant strings for the substrings “From: “ and “\nTo: “ for this class. Don’t forget the extra \n at the end of the “To” line and the message, however that does not need to be done as a constant.



(8 points)




Write a tester program as discussed in class, called MessageTester, that uses this Message class to make a message and print it. Ensure you test all methods and complete all 4 testing steps for EACH method.




(4 Points)




(3 points for file names, comments, style, et cetera)

CSE 271 –

Thursday Labs – Due Tuesday 11:59pm

Friday Labs – Due Wednesday 11:59pm






Part 2 (15 points)




Design a class, called Mailbox, that stores (a collection of) e-mail messages, using the Message class of Part 1. Create a single appropriate constructor that makes an empty messages collection, and initializes a Mailbox signature, as described below. In terms of the data for the mailbox, look to the “Collecting Values” pattern presented in lecture. You must implement the following three methods that manipulate the Mailboxes data appropriately.




public void addMessage(Message m)
public Message getMessage(int i)
public void removeMessage(int i)



Each individual mailbox (object instance) must have a constant string that represents its unique individual signature. This signature must be appended




to the end of each message after the message is added to the mailbox. (8 points)




Write a tester program MailboxTester that tests all methods and various cases as we laid out in the 4 steps in the lecture and textbook. In this tester, you will have to create Messages to properly test the methods. Ensure you test all methods and complete all 4 testing steps for EACH method. (4 Points)







(3 points for file names, comments, style, et cetera)




Tips




You do not need getters and setters for your classes today, but, of course, you may add any that you feel are appropriate. For example, a "setter" for the Mailbox's mailbox (arraylist) of messages, might not be appropriate.




You do not need to test your getters and setters. In the real world, you would only do that in cases where they were very complex, for example, if a getter involved a complex formula or calculation based on multiple instance variables.




For the get message and remove message methods, you have a couple of options regarding exceptions when i is out of range




Do nothing.



Add the throws clause to the signature (... throws XYZException)



Try and catch the exception that occurs.
CSE 271 –

Thursday Labs – Due Tuesday 11:59pm

Friday Labs – Due Wednesday 11:59pm






Submission




Turn in a .zip of your four .java files to Canvas by your appropriate due date. Ensure you have actually submitted (received confirmation and checked online), since no late labs will be accepted.




Message.java



MessageTester.java



Mailbox.java



MailboxTester.java



Grading will be based on conforming to the standards we reviewed in class as well as following the requirements of this lab.