public boolean addRequiredFile(String fileName) {

        // if the list is empty
        if (requiredFiles_ == null) {
            requiredFiles_ = new LinkedList();
        }

        // then check whether filename already exists or not
        boolean result = false;
        for (int i = 0; i < requiredFiles_.size(); i++) {
            String temp = (String) requiredFiles_.get(i);
            if (temp.equals(fileName)) {
                result = true;
                break;
            }
        }

        if (!result) {
            requiredFiles_.add(fileName);
        }

        return result;
    }