public boolean prefixAgain(String str, int n) {
    return (str.replaceFirst(Character.toString(str.charAt(n-1)),"").contains(Character.toString(str.charAt(n-1))));
}

prefixAgain("abcccccbx", 2);

public boolean prefixAgain(String str, int n) {
    boolean result = false;
    if (n < str.length() &&
            (str.substring(1)).indexOf(str.substring(0,n)) > -1
            ) {
        result = true;
    }
    return result;
}