It runs counter to variance rules for method signatures; see pron's sibling comment and my reply to that. I'm not exactly sure what he's alluding to in terms of

It runs counter to variance rules for method signatures; see pron's sibling comment and my reply to that. I'm not exactly sure what he's alluding to in terms of an actual solution, but he is an insider, so there may be hope for Java programmers :). Anyway, the key point is that any implementation of a method will (almost by definition) need to be able to throw more types of errors than the writer of the original interface anticipated. That is the fundamental problem and unless you get rid of overriding there's no solution for that. The only solution is to force everything into a single super-type... but that just leads to "throws Exception" and we've been there before. (I mean, there's approximations to solutions as in OCaml's polymorphic variants, row types, intersection types, etc. .. but those only work when variance isn't involved... or do away with most of the touted benefits of the "checked" part of checked exceptions, so...)