How can I simulate Haskell's “Either a b” in Java

Question

How can I write a typesafe Java method that returns either something of class a or something of class b? For example:

public ... either(boolean b) {
  if (b)         


        

Answer 1

The suggestions already provided, although feasible, are not complete as they rely on some null references and effectively make "Either" masquerade as a tuple of values. A disjoint sum is obviously one type or the other.

I'd suggest having a look at the implementation of FunctionalJava's Either as an example.