Playing devil's advocate here, could this feature make the language more expressive?
Take for example an API where you'd typically wrap a method call in try/catch blocks to handle the various "outcomes" e.g. a user login, you'd maybe have a UserDisabled exception, a UserAlreadyLoggedIn exception, a UserPasswordIncorrect exception, etc. With the addition of this syntactic sugar, the method could instead accept an anonymous class with a onDisabled, onLoggedIn, onPasswordIncorrect methods. Perhaps it would also have a performance benefit over cascading through catch blocks? Though someone else would have to confirm that.
