Description
A palindrome reads the same regardless of whether the letters are written forward or backward. Some
examples include “rotator”, “racecar”, and even phrases like “do geese see god” (palindromic phrases
tend to allow for creative placement of spaces).
This week’s program is a recursive exploration of palindromes, but we’re going to keep things very
simple: all you’ll do is work through the letters of the alphabet in a mirrored sequence. You’re tired,
we’re tired; let’s keep things as straightforward as we can. We’re not even going to do any
object-oriented programming this time. Everything is familiar and static.
Grading Rubric
©2021 Mouna Ayari Ben Hadj Kacem and Hobbes LeGault — University of Wisconsin–Madison
1
5 points Pre-assignment Quiz: accessible through Canvas until 11:59PM on 03/22.
15 points Immediate Automated Tests: accessible by submission to Gradescope. You will
receive feedback from these tests before the submission deadline and may make
changes to your code in order to pass these tests.
Passing all immediate automated tests does not guarantee full credit for the
assignment.
20 points Additional Automated Tests: these will also run on submission to Gradescope, but
you will not receive feedback from these tests until after the submission deadline.
10 points Manual Grading Feedback: TAs or graders will manually review your code to verify
use of recursion. If you implement your methods iteratively instead of recursively,
you will lose all of these points.
P06 Palindromes Pair Programming: NOT ALLOWED
CS 300: Programming II – Spring 2021 Due: 11:59 PM CDT on WED 03/25
Learning Objectives
The goals of this assignment are:
● Familiarize yourself with recursive problem solving techniques.
● Relax a little. We can’t give you a spring break, but we can try to give you a spring
hopefully-a-little-easier.
Additional Assignment Requirements and Notes
Keep in mind:
● You are allowed to define any local variables you may need to implement the methods in this
specification.
● You are allowed to define any private static helper methods you may need to help implement
the methods in this specification.
● All methods, public or private, must have their own Javadoc-style method header comments in
accordance with the CS 300 Course Style Guide.
● Any source code provided in this specification may be included verbatim in your program
without attribution.
● You may not have ANY import statements. This is a very simple program.
©2021 Mouna Ayari Ben Hadj Kacem and Hobbes LeGault — University of Wisconsin–Madison
2
P06 Palindromes Pair Programming: NOT ALLOWED
CS 300: Programming II – Spring 2021 Due: 11:59 PM CDT on WED 03/25
CS 300 Assignment Requirements
You are responsible for following the requirements listed on both of these pages on all CS 300
assignments, whether you’ve read them recently or not. Take a moment to review them if it’s been a
while:
● Academic Conduct Expectations and Advice, which addresses such questions as:
○ How much can you talk to your classmates?
○ How much can you look up on the internet?
○ What do I do about hardware problems?
○ and more!
● Course Style Guide, which addresses such questions as:
○ What should my source code look like?
○ How much should I comment?
○ and more!
Getting Started
1. Create a new project in Eclipse, called something like P06 Palindrome.
a. Ensure this project uses Java 11. Select “JavaSE-11” under “Use an execution
environment JRE” in the New Java Project dialog box.
b. Do not create a project-specific package; use the default package.
2. Create two (2) Java source file within that project’s src folder:
a. Palindrome.java (does NOT include a main method)
b. PalindromeTester.java (includes a main method)
All methods in this program will be static methods, as this program focuses on procedural programming.
©2021 Mouna Ayari Ben Hadj Kacem and Hobbes LeGault — University of Wisconsin–Madison
3
P06 Palindromes Pair Programming: NOT ALLOWED
CS 300: Programming II – Spring 2021 Due: 11:59 PM CDT on WED 03/25
Implementation Requirements Overview
Your Palindrome class must contain the following four (4) static methods, which must be implemented
recursively:
● public static String mirrorA(char start) throws IllegalArgumentException
○ Recursively create a simple alphabet pattern, starting at the provided character, moving
backward to the beginning of the alphabet, and then forward again to the provided
letter, separating each letter with a space.
■ If start is ‘E’, the method should return the string “E D C B A B C D E”
○ This method is only valid for capital letter input; if anything other than a capital letter is
provided as an argument, throw an IllegalArgumentException with a descriptive error
message.
● public static String mirrorA(char start, int step) throws
IllegalArgumentException
○ Recursively create an alphabet pattern, starting at the provided character, and moving
back and forth to the beginning of the alphabet by steps of size step.
■ If start is ‘E’ and step is 1, the method should return the same string as
mirrorA(start).
■ If start is ‘E’ and step is 2, the method should return “E C A C E”
■ If start is ‘E’ and step is 3, the method should return “E B B E”
■ And so on.
○ As before, the method is only valid for capital letter input and strictly positive (not zero
or negative) step sizes. For invalid input, throw an IllegalArgumentException with a
descriptive error message.
● public static String mirrorZ(char start) throws IllegalArgumentException
○ Recursively create a simple alphabet pattern, starting the provided character, and
moving forward to the end of the alphabet, and then backward again to the provided
letter, separating each letter with a space.
■ If start is ‘V’, the method should return the string “V W X Y Z Y X W V”
○ This method is only valid for capital letter input; if anything other than a capital letter is
provided as an argument, throw an IllegalArgumentException with a descriptive error
message.
● public static String mirrorZ(char start, int step) throws
IllegalArgumentException
○ Recursively create an alphabet pattern, starting at the provided character, and moving
forward and back to the end of the alphabet by steps of size step.
■ If start is ‘V’ and step is 1, the method should return the same string as
mirrorB(end).
■ If start is ‘V’ and step is 2, the method should return “V X Z X V”
©2021 Mouna Ayari Ben Hadj Kacem and Hobbes LeGault — University of Wisconsin–Madison
4
P06 Palindromes Pair Programming: NOT ALLOWED
CS 300: Programming II – Spring 2021 Due: 11:59 PM CDT on WED 03/25
■ If start is ‘V’ and step is 3, the method should return “V Y Y V”
■ And so on.
○ As before, the method is only valid for capital letter input and strictly positive (not zero
or negative) step sizes. For invalid input, throw an IllegalArgumentException with a
descriptive error message.
Some hints:
● Remember that char primitives are like ints — you can add and subtract integer values from
them, and they will change value in alphabetical order.
● The ASCII value of ‘A’ is 65, and the ASCII value of ‘Z’ is 90.
● The expression ‘A’ == 65 evaluates to true, as does ‘B’ > ‘A’.
Your PalindromeTester class must contain AT LEAST:
● public static boolean testMirrorA()
● public static boolean testMirrorAStep()
● public static boolean testMirrorZ()
● public static boolean testMirrorZStep()
○ These methods should test valid AND invalid input against expected results, and must
NOT throw exceptions.
● public static boolean runAllTests()
○ This method must call ALL of your test methods and return true if and only if all
methods return true. If you add additional methods besides the four listed above, be
sure to call them here.
● public static void main(String[] args)
○ The only line in this method should be a call to the runAllTests method.
Be aware that we will be testing your test methods on code which contains errors! Your methods should
be able to detect errors in code and return false in those cases.
©2021 Mouna Ayari Ben Hadj Kacem and Hobbes LeGault — University of Wisconsin–Madison
5
P06 Palindromes Pair Programming: NOT ALLOWED
CS 300: Programming II – Spring 2021 Due: 11:59 PM CDT on WED 03/25
Implementation Details and Suggestions
Make sure you’re implementing the methods in Palindrome.java recursively. You may wish to create an
iterative (looping) implementation in your tester class to compare results, but if you don’t write your
mirror methods using recursion, you will lose all of the manual grading points.
Approaching Recursion
To design a recursive method, I recommend starting with the base case(s):
1. For the non-step methods, the base case is just that the char argument is ‘A’ or ‘Z’.
2. For the step methods, you have two base cases: either the argument is ‘A’ or ‘Z’, or it’s exited
the alphabet and isn’t a capital letter anymore.
Figure out what the result String will look like for these cases, and implement that.
Then work on the recursive case: add the current character to either end of the recursive string of the
other characters.
Testing
We’ve given you some sample output for valid inputs that you’re welcome to use, but we encourage you
to come up with some other cases and be sure to test invalid inputs, too. Remember that your test code
should be able to detect errors!
©2021 Mouna Ayari Ben Hadj Kacem and Hobbes LeGault — University of Wisconsin–Madison
6
P06 Palindromes Pair Programming: NOT ALLOWED
CS 300: Programming II – Spring 2021 Due: 11:59 PM CDT on WED 03/25
Assignment Submission
Hooray, you’ve finished this CS 300 programming assignment!
Once you’re satisfied with your work, both in terms of adherence to this specification and the academic
conduct and style guide requirements, submit your source code through Gradescope.
For full credit, please submit ONLY the following files (source code, not .class files):
● Palindrome.java
● PalindromeTester.java
Your score for this assignment will be based on the submission marked “active” prior to the deadline.
You may select which submission to mark active at any time, but by default this will be your most recent
submission.
Copyright Notice
This assignment specification is the intellectual property of Mouna Ayari Ben Hadj Kacem, Hobbes
LeGault, and the University of Wisconsin–Madison and may not be shared without express, written
permission.
Additionally, students are not permitted to share source code for their CS 300 projects on any public
site.
©2021 Mouna Ayari Ben Hadj Kacem and Hobbes LeGault — University of Wisconsin–Madison
7
