g CS151

CS 151

Cover page image

Cay S. Horstmann

Lecture 3

Pre-class reading: Section 2.2 - 2.4, 2.7
Clicker questions
- Put your answer into Piazza
Lecture (Slides are here)
Lab
Discussion

Lecture 3 Clicker Question 1

Is the value 42 an object?

Yes
No, it has no state
No, it has no behavior
No, it has no identity

Lecture 3 Clicker Question 2

Consider designing a system where students can take online quizzes such as this one? What would not make a good class?

Student
Question
EvaluateResponses
WrongAnswer

Lecture 3 Clicker Question 3

In the voice mail system, consider the responsibility:

Remove a message from a mailbox

Which class should be responsible?

Mailbox
User
Message
MessageQueue

Lab

Work with a buddy
One of you (the “coder”) codes, the other (the “scribe”) types up the answers.
One of you submits the code in the lab2 subdirectory of your personal repo, the other submits a file report.txt in the lab2 subdirectory of your repo.
Put the name of the coding buddy into the report
Push your repo when you are done
You don't have to complete all parts, but you have to be present and do your best.

The Lab Report File

Scribe: Make a directory to hold your lab work and put an empty file in it.
```
cd ~/cs151
mkdir lab3
touch lab3/report.txt
```
Make sure it's lab3 with lowercase letters and no spaces. Now open the file in your favorite text editor.
Coder: Also make such a directory. This is a non-coding lab, but we'll do work on paper. Take photos and put them in your repo. (You can do this later.)

A Piazza Simulation

We want to design a program that simulates Piazza in the same way that the voice mail simulation simulates a real voice mail system.

Jointly come up with a list of classes that you think will be needed.

Scribe: Write down the classes that you came up with

Scenarios

Think of the key scenarios that are happening in Piazza. One of them is: “Student asks a new question”. Write down other scenarios that are useful and that one might want to include in the simulation. (Stay away from complicated stuff like adding images or HTML editing.)

Scribe: Write down the scenarios that you came up with

CRC Cards

Make a CRC card for each class that you discovered. Start playing through the three most interesting scenarios. Which classes are responsible for what?

For example, consider “Student asks a new question”. Do you have classes Student and Question? A class that manages a list of questions? Which class is responsible? And what is the responsibility?

You may discover new classes as you do this. That's ok.

Coder: When you are done, take photos of the CRC cards.