Smalltalk, it is an experience, given that language, IDE and runtime/OS are all blended together, while Java can only do so much, even with the more advanced IDEs.
Clojure might be a reaction to C++/Java/C# OOP style, but it surely adopts Common Lisp OOP style.
I think if things have private state that can't be seen externally and that's idiomatic then there's a conflict, if not then there isn't. Do you think it's worth learning Smalltalk? Is it still possible?
Smalltalk