The idea is that you deconstruct when a method returns a sum type: An interface with a defined set of implementers that doesn't change. A very common pattern in

The idea is that you deconstruct when a method returns a sum type: An interface with a defined set of implementers that doesn't change. A very common pattern in, say, Haskell or Scala. In Scala you'd also get a warning if you forgot to check one possible type to deconstruct. If you aren't defining your data types like that, yeas, it's a bit weird. This, along with the underscore, and even the sequence type, shows that the language designers are well aware of what Scala does, and are picking and choosing which things to bring in without risking exposing Java devs to the traditional monad salads that you see in many a Scala codebase.