Take the 2-minute tour ×  There are already a few questions
regarding the fact that methods in GWT RPC should not return an
interface like List, but rather a concrete class like ArrayList,
because otherwise "GWT needs to include all possible
implementations". See e.g. In GWT, why shouldn't a method return
an interface?  Here's my question: is this limited to the return
type itself? How about parameters of the method? And what if the
return object contains an interface, e.g.  public class
MyReturnObject implements IsSerializable {    List<String>
listOfUnspecifiedType1;    List<Long> listOfUnspecifiedType2;
The examples I have seen all talk of the return type itself. I
don't see why it would be a problem to return an interface, but
not a problem to return an object which just wraps an interface;
but maybe I am missing something?  share|improve this question
add comment  1 Answer  up vote 2 down vote accepted  It's clear
from the linked question that it applies recursively (and as
soon as you understand why yo