Doxygen vs Javadoc

Question

I just realized from an article in CACM that Doxygen works with Java (and several other languages) too. But Java has already the Javadoc tool. Can someone explain what are the pros and cons of either approach? Are they mutually exclusive? Is there a Maven plugin for Doxygen?

Answer 1

I'd only use Doxygen with Java if you're new to Java and you've used Doxygen before, reducing the learning curve you'd experience with javadoc. If you haven't used Doxygen before, I'd stick with javadoc, since it was specifically designed with Java in mind. If you don't know either one, and you work in C++ (or other supported languages) as much as you do Java, Doxygen is a good choice, as you'll be able to use it for both languages.

Both tools are easy to use, with a similar feature set. Both have plugins (or are pre-built in) for NetBeans and Eclipse making it even faster to generate doc. There is a lot of overlap in the comment style used by each, but they're not exactly the same, so it would be difficult to mix them together (you'd have to know the details of both, leaving out any features that are specific to one or the other). I've never used it, but there does seem to be a Maven plugin for Doxygen.

Answer 2

I like the fact that with Doxygen, you can get class diagrams displayed on the same page as the documentation. Also, I like the fact that it links you directly to the source code, if needed. I am not aware if javadoc has these features though.

Answer 3

Doxygen has a number of features that JavaDoc does not offer, e.g. the class diagrams for the hierarchies and the cooperation context, more summary pages, optional source-code browsing (cross-linked with the documentation), additional tag support such as @todo on a separate page and it can generate output in TeX and PDF format.It also allows a lot of visual customization.

Since Doxygen supports the standard JavaDoc tags you can run Doxygen on any source code with JavaDoc comments on it. It often can even make sense to run on source code without JavaDoc since the diagrams and source code browsing can help understanding code even without the documentation. And since the JavaDoc tool ignores unknown tags you can even use additional Doxygen tags without breaking JavaDoc generation.

Having said all this I must admit that I haven't used Doxygen for a long time. I tend to rely heavily on my IDE nowadays to provide the same visualization and I usually don't read JavaDoc as HTML pages but import the source files into my IDE so it can generate JavaDoc flyouts and I can jump to the definitions. That's even more powerful than what Doxygen has to offer. If you want to have documentation outside the IDE and are happy to run non-Java tooling then Doxygen is worth a try since it doesn't require any change to your Java code.