blastr | Audible information radiator for commit messages | Runtime Evironment library

The common supertype of the classes you want to support — and considering your Supportable type — is Object however, if you define your class to inherit from Object (which is by default) and implements Supportable there is no way you can restrict your generic class this way.

if I were you, I would have used a Factory pattern and write a method that accepts any thing (subclass of Object) and its type to instantiate a relevant instance of Bla . The Create method should be generic but you can not impose any restriction here only you may be able to throw an exception if the type is not acceptable. I know, it is not the type of answer that you are probably expecting. But there is no other way (in your case).

P.S For those who think OP is doing something wrong, and we should not have such a design in real world. I would like to introduce an example. Assume you are about to write a class which suppose to create an in-memory table (like what we do in databases but with java data types). You also want to support user’s data types! So how would you do that?