How do I modify the Javadoc when I modify someone else’s code?

Those comments do not belong in the javadoc 🙂 The javadoc should explain the contract — it is what is extracted and displayed in the auto-generated “documentation”. The rest are just normal comments or, perhaps better yet in this case, SCM log entries and have no place in the javadoc!

I would likely just leave the original author, but if you want credit…

…see the @author javadoc reference and note that it can be included multiple times. This section explicitly relates to multiple authors and ordering, etc.

/**
* This class does some really awesome stuff.
* It uses PostreSQL. 
*
* @author Steph the Great
* @author Freddy Four Fingers
*/
// DEC2012 - Fred - Modified to use PostgreSQL instead of Derby (but really, use SCM!)
class Awesome { ... }

Happy coding.

Notes on question somewhat unrelated to example in post… if the author isn’t known, then several things can be done. First and foremost add a link or reference to where the original source was obtained — an optional “I didn’t write this originally” for clarity can be noted as well.

Then, depending upon your preference:

1. Don’t specify an @author field — not even yourself. It’s not required.
2. Add yourself as the sole author; the original source is mentioned above in the javadoc
3. Add a dummy author and yourself as the second author, e.g. @author Unknown @author unascribed (see comments and @author).
4. Do whatever you want within terms of the license, if any.