Java APIs

Hello

I do not know if this is the best place for this post, but after searching for "java documentation best practices" in google the results were not very clear and direct.

For instance, I have an interface (e.g. ExampleInterface) and a Class (e.g. ImplmentsExampleInterface) that implements the ExampleInterface.

The "ImplmentsExampleInterface" will have no code, just the "ExampleInterface" overwritten methods and then I will have several other Class's that will extend "ImplmentsExampleInterface", and it will be this Classes that will contain the code.

I only ask for pointers to proper place that has examples and information on how to properly comment/document this kind of structure, for instance, should I document everything (interface, super class, and class's) even if it is copy paste? Or should I put the effort in commenting the diferences betewen the bottom Class's?

Regards
Cad