Pre-Assignment 7: Arrays

The goal of this assignment is to practice writing with arrays. This part is a warm-up so you can come to lab-day on Friday having already thought about arrays and perhaps having some questions.

1. Setup

As in previous assignments, move into your cs241 directory. Make a directory for this assignment, and change into it.

> cd cs241
> mkdir assign7
> cd assign7

Like last time, I am giving you partially-written files to start with. For this part, copy one file from the public directory:

> cp /homeemp/tvandrun/pub/241/ManyPalindromes.java .

2. Homemade charAt

Notice that the method palindromeIterative differs from what you did last time in that it doesn't call text.charAt(). Instead, it calls a method defined locally, called homemadeCharAt. Write the body of that method. It should work exactly like charAt and it should use the string method (some string).toCharArray() which will return an array of characters that is equivalent to the string. For example, in the code

        String str = "hello";
        char[] array = str.toCharArray();

array is set to {'h', 'e', 'l', 'l', 'o'}.

Don't make this harder than it needs to be--- this can be done in one line!

Compile and test. The easiest way to make sure that it works is to explicitly call palindromeIterative on some strings in the main method, like

        System.out.println(palindromeIterative("wheaton"));
        System.out.println(palindromeIterative("racecar"));

3. Command line arguments

Remember that we've noticed that the main method has a parameter--- it's an array of Strings. The Java Virtual Machine creates that array based on what the user types at the command line when starting your program. For example, if someone were to type

> java YourProgram hello my name is someone

then the main method in the program YourProgram would be passed an array of the five strings that follow the name of the program:

{"hello", "my", "name", "is", "someone"}

This time, instead of prompting the user for palindromes, we'll use the strings on the command line and test them. So, in your main method, delete all the testing code you had from the earlier section. Then write a loop that iterates through the elements of args. For each one, print it and display whether or not it is a palindrome. A sample run might look like

> java ManyPalindromes wheaton level radar computer
wheaton false
level true
radar true
computer false

Compile and test.

You'll hand this in later with the rest of this assignment.