Checking to see if a string is alphabetic
It's not harder than this:

public static boolean checkAlphabetic(String input) {
    for (int i = 0; i != input.length(); ++i) {
        if (!Character.isLetter(input.charAt(i))) {
            return false;
        }
    }

    return true;
}


The idea is to return false as soon as you encounter a character c for which Character.isLetter returns false. If no such, return true since the string does not contain non-letter characters.