public String next() {
    int start = page * pageLength;
    int end = start + pageLength;

    if (end >= text.length()) {
        end = text.length() - 1; // last character in the book
    } else {
        page = page + 1; // only turn the page if we are not at the end of
                        // the book
    }

    if (start > text.length()) {
        return "end";
    }

    return text.substring(start, end);
}