class FilenameUtils {

    public static String getPrefix(String filename) {
        if (filename == null) {
            return null;
        }
        int len = getPrefixLength(filename);
        if (len < 0) {
            return null;
        }
        if (len > filename.length()) {
            return filename + UNIX_SEPARATOR;  // we know this only happens for unix
        }
        return filename.substring(0, len);
    }

    public  FilenameUtils();

}