Generating Cipher Alphabet

Question

I am to generate a cipher alphabet (based on Caesar Cipher) given the user-inputted shift key, and my code seems to be wrong.

I don't understand what's wrong with my cipherAlphabet method because whenever I try to test out the result, it just ends up giving me an error of "java.lang.ArrayIndexOutOfBoundsException: 26."

So, it probably has something to do with going past the arrays I set, but I cannot see this. I know this is probably something really simple, but could someone help me out?

P.S. - I tried looking for existing hints on SO and other websites for some help, but to no avail.

I would do all the conversions and encryption in one method, but I can't do that unforunately (apparently, I have to do this). Here's what I have:

private String message;
private static int shiftKey;
public static final String[] ALPHABET = {"A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "N",
                                         "M", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"};
public static String[] cipherAlphabet = new String[ALPHABET.length];

/**
 * Constructor for objects of class CaesarShiftEncryption
 */
public CaesarShiftEncryption(String m, int shift)
{
    message = m;
    shiftKey = shift;
}

public static String[] cipherAlphabet()
{
    for(int i = 0; i < ALPHABET.length; i++)
    {
        if(i >= 23)
        {
            cipherAlphabet[i] += ALPHABET[26 - shiftKey];
        }
        else
        {
            cipherAlphabet[i] += ALPHABET[i + shiftKey];
        }
    }
    return cipherAlphabet;
}

Answer 1

You need to start over! Try something like this, using the mod operation, you'll restart at the beginning of the alphabet, if you happen to hit the end

cipherAlphabet[i] += ALPHABET[(i + shiftKey) % ALPHABET.length]