CS 151

Cover page image

Day 5

Pre-class reading: 3.1 - 3.4 and run the sample code before class
Clicker questions
- Put your answer into Piazza
Lab
Discussion

Day 5 Clicker Question 1

In Chapter 3, the author designs a Day class even though there are already perfectly good classes in the java.time package. Which class could you use to represent calendar days?

Instant
DayOfWeek
ZonedDateTime
None of the above

Day 5 Clicker Question 2

Three versions of the Day class are presented in this chapter. What is this meant to demonstrate?

Encapsulation
Evolution
Separation of accessors and mutators
Side effects

Day 5 Clicker Question 3

Consider the following classes:

public class Post 
{
   private Response studentResponse = new Response();
   private Response instructorResponse = new Response();
   . . .
   public Response getStudentResponse() { return studentResponse; }   
   public Response getInstructorResponse() { return instructorResponse; }
   . . .
}

Which of the following statements is true?

This is a violation of encapsulation.
This is a violation of the Law of Demeter.
This public interface is not cohesive.
These methods have a side effect.

Lab

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 lab5 subdirectory of your personal repo, the other submits a file report.txt in the lab5 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.

Running JShell

Open a terminal and run
```
cd ~/cs151
mkdir lab5
jshell
```
In the interactive Java shell, type
```
import java.time.*;
Instant.now()
```
What happens?

Type

var newYear = ZonedDateTime.of(2000,1,1,0,0,0,0,ZoneId.of("America/Los_Angeles"));
newYear.plusDays(1000)

Type
```
/exit
```
to exit JShell. Then copy the Day.java file from the oodp3code/ch03/day3 directory to the current directory (.). Open the Day.java file in jshell and construct an instance:
```
cd ~/cs151/lab5
cp ~/oodp3code/ch03/day3/Day.java .
jshell
/open Day.java
var newYear = new Day(2000, 1, 1);
```
What happens?
This would be cooler if Day.java had a toString method. Edit Day.java with a text editor of your choice. Add this method:
```
public String toString()
{
   return String.format("%04d-%02d-%02d", year, month, date);
}
```
Reload Day.java in JShell (with /open) and try the previous command again. What happens?
Run
```
newYear.plusDays(1000)
```
What happens? Why?
How did you fix it?

Compiling/Running from the Command Line

Coder: The following assumes that you cloned the book code repo into ~/oodp3code in the lab for lecture 2. Verify that's correct, and otherwise adjust the instructions. Or, if you've never done it, go back to lecture 2 to see how to do the cloning.
In a terminal window, type
```
mkdir ~/cs151/lab5
cp -R ~/oodp3code/ch02/mail ~/cs151/lab5
cd ~/cs151/lab5/mail
javac *.java
java MailSystemTester
```
What happens?
Type commands to connect to mailbox 14, type a message, hang up, dial mailbox 14 again, and read the message. Hit Q to quit the program.
Put all the keystrokes that you just typed in a file ~/cs151/lab2/mail/keys.txt
Now let's see if you captured the keystrokes just so. Run
```
java MailSystemTester < keys.txt
```
What happened?
If everything was right, then you should see the output of the preceding program run on the screen. If your last keystroke was Q, the program should have terminated, and you should get a prompt back. If not, hit Ctrl+C to kill the program and fix up keys.txt
NOTE: The grader will do this for homework 3.
NOTE: If you do this in a project that you compiled in Eclipse, the class files will be in a bin directory. In that case, run
```
java -classpath bin MailSystemTester < keys.txt
```

The .gitignore File

Coder: Type git status. Scribe: What files do you see that should not be checked into the repo?
Don't add class files or Eclipse configurations to a repo. Class files can be obtained by recompiling. Eclipse configurations contain icky path names like c:\Program Files\whatever that are meaningless on other systems.
Run git rm --cached file or git rm --cached directory to remove any files that you want to suppress. The --cached means that the files won't be deleted from your local directory.
Now run git status again. What is the difference?
Using your favorite text editor, make a file .gitignore in the ~/cs151 directory. (Note the file name has ten characters, including a period in the front.) Add the following lines:
```
**/*.class
.project
.classpath
.settings
```
(If you use IDEA or NetBeans, add whatever is needed to filter out those configurations.)
Now run git status again. What is the difference?
At this point, both the coder and the scribe should have a clean git status. If not, run git add to add any files that you previously forgot to add. Then run git commit and git push
Both of you should check your BitBucket/Github site to make sure that all files are where they should be.

Directory names

Both coder and scribe: Run
```
cd ~/cs151
ls -a
```
What happens?
The . and .. directories are the current and parent directory. The .git directory contains files that Git needs. You should see a file hw1scores.txt. Don't mess with any of those. Then you should see seven directories hw1, hw2, lab1, lab2, lab3, lab4, lab5. All in lowercase. No spaces, underscores, dashes, etc. There should be no other directories.
Is that what you see?
If not, it's time to clean up. Use the command git mv to move a directory, and to tell Git what's happening. (If you just use mv, then Git will cry loudly that the old directory was lost and it doesn't know the new one.) For example,
```
git mv "HW 1" hw1
```
If there is a file that shouldn't be there at all, run git rm to remove it. This will remove it from your computer as well, so don't do that with files that should be in .gitignore.

Discussion

discussion