I’m a big fan of checked exceptions, which are niche in the sense that only Java has them (at least among popular programming languages). However, Java lacks the ability to parameterize code over sets of exception types, which places limitations on how checked exceptions can be used with type-generic code. That’s something that can be improved.

Exceptions allow more flexibility in separating the success-case program flow from the error-case program flow, compared to return codes or union return types. Unchecked exceptions, however, have the same drawbacks as dynamic typing does. Checked exceptions are the static-typing equivalent.