First repeated character in string

 public static void main(String[] args) {

        String input = "Automata";
        System.out.println(firstRepeatedChar(input));

    }

    static char firstRepeatedChar(String input){
        int[] alphabet = new int['z' - 'a' + 1];

        for (int i = 0; i < input.length(); i++) {
            char current = input.toLowerCase().charAt(i);
            if(alphabet[current - 'a'] == 0){
                alphabet[current - 'a']++;
            } else {
                return current;
            }
        }
        return '\0';
    }