`() -> A::new` is a function which returns a function which returns an A. (or, a function which returns a no-arg constructor)

From [the spec](https://docs.oracle.com/javase/specs/jls/se8/html/jls-15.html#jls-15.27.3)

> A lambda expression is congruent with a [void-producing] function type
> if ... the lambda body is either a statement expression (§14.8) or a
> void-compatible block.

So this function which returns a function **IS** an `IConverter` because it accepts no arguments, and even though it returns something, the item it returns is able to be ignored. That is, it's *void-compatible*.

So the constructor is dropped on the floor and never invoked.

What you meant was

    enum FactoryEnum {

      CLASS_A(A::new),
      CLASS_B(B::new);

Now, it's not a function which returns a function. It's just a function.