Lab 7: Recursive methods

The goal of this lab is to practice writing and working with recursive methods.

1. Setup

As in previous assignments, move into your cs235 directory. Make a directory for this assignment, and change into it.

cd cs235
mkdir lab7
cd lab7

Copy the file PalindromeTest.java from the public directory for this class:

cp /homeemp/tvandrun/pub/235/PalindromeTest.java .

2. Reversing a string iteratively

Reversing a string is a simple matter of looping through it and using charAt and concatenation to construct a new string backwards. Fill-in (and document) the body of reverseIterative using this algorithm. Then test it using the main method.

3. Reversing a string recursively

This can also be done recursively. Think of a way to formulate the problem (that is, define what the reverse of a string is) recursively. Then implement it in a method, reverseRecursive.

2. Computing palindromes iteratively

A couple assignments ago you each wrote a method to determine whether or not a String is a palindrome. We will be doing that again, but with two different algorithms. Fill-in the body of palindromeIterative, using this algorithm:

• Reverse the string (using one of your reverse methods), and store in reversed.
• Test if reversed is equal to text (be careful!).

Compile and test.

3. Computing palindromes recursively

Now do the same for palindromeRecursive, except using a recursive algorithm. Your method palindromeRecursive must call itself. Figure the algorithm on your own, but here's a recursive definition of a palindrome to get you started:

A palindrome is

• an empty string,
• a string with exactly one character,
• or the string that results from prepending and appending the same character to a palindrome.

(Remember, "prepend" means "concatenate to the front" and "append" means "concatenate to the back.")

4. Turn in

Create the script file as before (cat, rm, compile, and run). Run the program using a variety of words, palindromes and not, using both the iterative and recursive versions. Print it out and hand in a hard copy.

a2ps -P sp (the name of the script file)