@Override
    public String toString() {
        StringBuilder string = new StringBuilder();

        string.append(super.toString());
        if (this.journal != null) string.append("Journal: ").append(this.journal).append("\n");
        if (this.volume != null) string.append("Volume: ").append(this.volume).append("\n");
        if (this.number != null) string.append("Number: ").append(this.number).append("\n");
        if (this.pages != null) string.append("Pages: ").append(this.pages).append("\n");

        return string.toString();
    }