In the old doclet world, doclets did not need to implement interfaces or abstract classes; they just had to have the right methods.

In the new worlds, classes which claim to be possibly partial impls of doclets should implement the Doclet interface.

This applies to HTMLDoclet and AbstractDoclet.

---

I suggest the following:
1. in the new StandardDoclet, look at the methods and that which they delegate to. Most are OK. Rename HtmlDoclet.sourceVersion to HtmlDoclet.getSupportedSourceVersion

2. Change AbstractDoclet to implement Doclet. The class is already abstract so missing methods will not be an issue.

3. Change all override-uses of the methods in Doclet to have @Override annotation. This will be in AbstractDoclet, HtmlDoclet and StandardDoclet.