I read the Java tutorial on default methods and I think I understand how interfaces may evolve without loss of backward compatibility. My question refers rather to how should we design our interfaces from scratch. If and when should we define default methods? As an extreme example, why not design MyNewInterface with all default methods? If some operation makes sense, fine, stick the appropriate code in there, and if not, just do nothing, return null, return 0, return false. This would give the implementers of my interface quite some freedom what to care about, depending on their application needs and would make their apps less verbose (kind of like what the awt Adapter classes achieve). I don't look for an approval of this approach, but at some guidelines. Hope this makes sense.
Edit: And one more question from someone involved a lot with libraries for external clients. Does it make sense to rewrite old interfaces in a new release of the library and turn some methods into default methods containing code that makes sense? This option was not available so far and users had to write sometimes trivial implementations.