HW2: First foray into Java [IND]


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HW2: First foray into Java [IND]

The goal of this assignment is to help you some practice writing your first Java programs.
In particular, you will get more practice with retrieving and using input from a user, loops,
printing output to the screen, and using some of the provided Java classes
(Scanner, StringBuilder, StringJoiner). Getting comfortable with the basics of Java will
set you up well for future assignments in this class.
There are no outside files that you will need for this assignment. However, this is a good
time to get yourself setup for future assignments.
Choosing an editor
One big part of that will be deciding what editor or program you will use when writing
code. There are many good options to choose from. In CS 111 you likely used
either Brackets or TextWrangler (both of which are installed on the lab machines). Either of
those are good options to continue using this course. To see all the editors installed on the
lab machines, go to Applications/CarletonApps. If you want to try something different,
here are a few more options.
• Emacs – This is an incredibly powerful editor that has been around forever. Beware,
there is some amount of start-up cost when you first start using Emacs, but here is
a tour that might be helpful. Like Vim or Vi, you can usually rely on it being installed
on most UNIX machines (just type emacs into a terminal prompt).
• Aquamacs – This is a Mac specific version of Emacs that is also installed on the lab
• Vim or Vi- This is another incredibly powerful editor that has been around forever
(though it also has quite a start-up cost to get through). It has the advantage that
essentially any UNIX system (Mac or Linux) always has it installed, and it is very
lightweight and starts up quickly. You can start it in a terminal window in any Mac
or Linux system by typing vim or vi at a terminal prompt.
A different type of option is using what’s called an integrated development environment
(IDE). These are programs that are designed to help people code – they often make it
easier to organize large projects and have some features to make coding easier (those
features vary based on the IDE, but may include a debugger to step through your code line
by line, code completion to help you remember the names of methods, or compiling in the
background and showing you the line an error occurred on). However, they can also add
extra overhead in terms of having to learn how to use the IDE and learn how to use Java.
For that reason, I’m not going to talk about IDEs in class. If you take more CS courses
such as software design, you’ll learn lots about IDEs. If you want to explore IDEs on your
own, you’re welcome to. There are a number of options out there, but I would
recommend IntelliJ as a particularly strong one.
Installing Java
Java is installed in the computer labs on campus (both in the CMC and elsewhere). But if
you have your own machine and would like to use it for this class, you are welcome to
install Java on your own computer as well using these instructions on the CS department
website. Note that the only officially supported environment is the lab computers, but Mike
Tie ([email protected], CMC 305) can help you troubleshoot if you run into problems
installing Java on your home computer; I’m also happy to try to help you during office
hours if you run into problems.
Your Assignment
This a solo assignment – you should not work with a partner. The reason for this is to make
sure that everyone feels comfortable writing a short program on their own. All of your code
files should include your name at the top (in comments). You can ask questions on Slack
or talk to me, the lab assistants, or the prefect if you’re having trouble. The appendix of
your book is also very helpful for Java syntax. Moodle has a link to the Javadocs for Java –
these are incredibly useful as a reference! (I often refer back to Javadocs when writing
code – that’s what they’re there for!)
For this assignment you’ll be creating a small Welcome to Data Structures App. You
should put all code for this assignment in a file called All of the functionality
of your App will be contained in the main method. In particular, your program should
complete the following tasks in the specified order:
1. Print to the screen “Welcome to CS 201: Data Structures!”
2. Ask the user for their name and use the Scanner class to retrieve the user input.
3. Ask the user to enter an integer (…, -2, -1, 0, 1, 2, …) and use the Scanner class to
retrieve the user input.
4. Print to the screen “Welcome [name]” where [name] is the name the user typed in.
5. Print to the screen “Your name backwards is [backwards]” where [backwards] is
the name the user typed in displayed backwards. You may find
the StringBuilder class from the reading useful here.
6. If the the number n entered by the user was positive, print off a triangle of numbers
like the following example where n=3. (I suggest using the StringJoiner class from
the reading.)
7. 1
8. 2,2
9. 3,3,3
10. Otherwise, if the the number n entered by the user was negative, print off a triangle
of numbers like the following example where n=-4. (I suggest using
the StringJoiner class from the reading.)
11. -1
12. -2,-2
13. -3,-3,-3
14. -4,-4,-4,-4
15. Otherwise, the number was 0, and just print “Cannot print a triangle of height 0.”
For example, here are a few possible runs of the program and what the output might look
$ javac
$ java Welcome
Welcome to CS 201: Data Structures!
What is your name: Eric
Enter an integer: 5
Welcome Eric
Your name backwards is cirE
$ javac
$ java Welcome
Welcome to CS 201: Data Structures!
What is your name: Schiller
Enter an integer: 0
Welcome Schiller
Your name backwards is rellihcS
Cannot print a triangle of height 0
Last Required Challenge: Modify your code so that if a user does not enter a valid
integer, the program prints out the warning “You must enter an integer” and then quits.
Optional Challenge: Modify your code so that instead of quitting when a user does not
enter an integer when prompted, the program just keeps re-prompting them to enter an
integer until valid input is obtained.
Final Hints
• Make sure to fully test your code. Try out positive and negative numbers as well as
integers and real numbers. The documentation for the Scanner class may be very
helpful to look at as you try to figure out how to do all of this.
• Look back at examples from class or your book if you get stuck. It’s totally okay to
experiment and try out methods to see what will happen – that is all part of the
learning process.
• Make sure to save your work regularly as you go along!
• If you get stuck, don’t hesitate to ask for help from a lab assistant, prefect, or me!
Submission and Grading
You’ll submit to Moodle as a zipped file. We’ll be using zip for all
submissions this term, so it’s a good habit to get into now. In particular, put
your file into a directory named [your\_last\_name]HW2, zip this directory,
upload it to Moodle. For example, my directory would be named AlexanderHW2 and the
resulting file would be
Hints for zipping a file or directory
• From the command line: You can zip files from the command line using the
command: zip -r [Name for zip file] [Name or directory of file to add
to zip]. For example, zip -r AlexanderHW2 will create the zip
file that contains the directory AlexanderHW2 and all files
contained inside that directory. The -r means “recursive” and is what tells zip to
include all files in the directory in the zip file.
• On a Mac: Select the folder you want to zip. Then right click (or sometimes hold the
command key and click). You’ll see a little menu pop up. Choose the option that
starts with “Compress”. For instance, if I had selected AlexanderHW2, it would say
“Compress AlexanderHW2”. This will produce a new zip file
• On a PC: Just as for a mac, selection the files/folders and right click. Select “Send
to” in the menu, and then click “Compressed (zipped) folder”.
This assignment is worth 16 points. Below is a partial list of the things that we’ll look for
when evaluating your work.
• Does the program compile? It is essential that you check whether your submitted
work compiles. If you submit a program that doesn’t compile, you will automatically
receive at least a 25% deduction for the assignment, even if the problem was
relatively minor.
• Does the program run correctly on test input?
• Does the program use Scanner, StringJoiner, StringBuilder correctly?
• Does the program handle positive/negative numbers and non-integer values
• Are comments used throughout the program to describe logic decisions?
• Is the program named Please make sure to always use any names
specified in an assignment.
• Does the program use Javadoc style comments at the top that include your name
as the author of the code?
Start early, ask lots of questions, and have fun! Eric, the lab assistants, and the prefect are
all here to help you succeed – don’t hesitate to ask for help if you’re struggling!
This assignment was modified from one written by Layla Oesper.

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