public String get(int n) {
        if (capitalword_) return null;
        int len = grams_.length();
        if (n < 1 || n > 3 || len < n) return null;
        if (n == 1) {
            char ch = grams_.charAt(len - 1);
            if (ch == ' ') return null;
            return Character.toString(ch);
        } else {
            return grams_.substring(len - n, len);
        }
    }