San Jose State University | CS 151 - OO Design Section 5 | Fall 2016

Homework 2

This is a multi-part homework that extends over several weeks. Put all work into a directory hw2 of your Git project and push it each week.

Remember to run git commit at least once a day to get full points.

Part A

We want to implement a text messaging system that is somewhat similar to the voice mail system in the textbook. Here is a typical user interaction (inputs in bold):

Welcome to TextChat.
[L]ogin  [N]ew user  [Q]uit:
N
Select a user name:
fred
Select a password:
secret
User added.
Welcome to TextChat.
[L]ogin  [N]ew user  [Q]uit:
L
User name:
fred
Password:
secret
Welcome fred.
[S]end message  [R]ead messages  [L]ogout:
S
To:
mary
Message text, . to end:
Hi Mary, what's up?
Etc. Etc.
.
Message sent.
[S]end message  [R]ead messages  [L]ogout:
R
From: mary
Hi Fred, what a surprise.
Etc. Etc.
[K]eep  [E]rase
K
[N]ext  [D]one with messages
D
[S]end message  [R]ead messages  [L]ogout:
L
Welcome to TextChat.
[L]ogin  [N]ew user  [Q]uit:

Provide the following in the hw2 directory:

1. We will have classes Message, Mailbox, MessageQueue, MailSystem like in the textbook. But does the Mailbox have a user name and password? Shouldn't that be a User? And there is no Telephone. Instead, use a class Console for interfacing with the user. Provide CRC cards for classes Mailbox, MailSystem, and Console. Write them out on real index cards and take a photo. Save it as crc.jpg.
2. Provide a plain text file crc.txt in which you explain, for each collaborator, why it is a collaborator. What is an object of the class going to ask the collaborating object to do, and when?
3. Draw a UML class diagram of the relationships between your classes. You can draw on paper and submit a photo or use a UML program or web site of your choice and turn in an image file (not the data file). Save it as uml.png
4. Provide a plain text file uml.txt in which you explain, for each association and dependency, why an object of one class has, or uses, an object of the other.

Part B

• Implement the messaging system. Provide classes Console, Mailbox, MailSystem, MailSystemTester, Message, MessageQueue, User. Put all classes in the default package.
• Submit all files to the hw2 repo. (The same one that you used last time.)
• The grader will run tests such as the following:

  cd hw2
  javac *.java
  java MailSystemTester < input.txt > output.txt
  diff output.txt expected.txt
  

  Here is a sample input.txt and expected.txt.
• If a user hits the wrong key for a menu, just repeat the menu with no further error message: input2.txt and expected2.txt
• If a user tries to send a message to a non-existent user, write "Message not sent." instead of "Message sent." after reading the message text: input3.txt and expected3.txt
• If a user types in a non-existent username/password, print no error message but repeat the login prompt: input4.txt and expected4.txt
• If a new user tries to make an account with the same name as an existing user, print “User not added.”: input5.txt and expected5.txt
• When user reads messages and prints the N key, show the next message just like you showed the first one. When there are no more messages as the user hits the N key, don't print an error message but instead return to the "[S]end message [R]ead messages [L]ogout" prompt: input6.txt and expected6.txt
• Submit a file hw2b.txt in which you explain all of the parts of your implementation that ended up being different or nonexistent in your homework 2A design. Do not update your homework 2A design documents.
• Draw a UML sequence diagram where an existing user logs in and checks two messages, keeping one and discarding the other. Don't draw it by hand. Use a tool to draw it, as suggested in chapter 2. Save it in a file sequence.png.