public class AlphabetTest {
    public static String FSAAcceptableCharacters = "abc";

    public static void main(String[] args) {
        String fileStr  = returnFileContent();

        System.out.println(fileStr); // making sure we read the right file

        try {
            for(int i = 0; i < fileStr.length(); i++) {
                if(!Character.isLetter(fileStr.charAt(i))) { // alphabet test
                    throw new Exception("Character '" + fileStr.charAt(i) + "' is not in the alphabet");
                }

                String s = "";

                if(FSAAcceptableCharacters.indexOf(s + fileStr.charAt(i)) == -1) {
                    throw new Exception("Character '" + fileStr.charAt(i) + "' is not in the FSA accepting part of the alphabet");
                }
            }

            System.out.println("No faulty character found"); // in case no faulty characters are found
        } catch(Exception e) {
            System.out.println(e.getMessage()); // show the error in the console
        }
    }