java and the interactive subsystem

Having used C# on and off since the start of the year the lesson has
slowly dawned on my as to why C# is a better language than C++. 
Despite the fact that c++ is hands down more feature rich than c#, c#
is clearly better.

The reason is managed code. Managed code allows the programmer to do
two core functions with ease. Return an object from a function call
without the necessity of copying all the bytes of the object ( in c#
you return a reference to the object.  in traditional languages like
c++ and rpg you return a copy of the object ).  By the same mechanism,
managed code allows an object to be added and removed from a
collection or list without the performance penalty of having to copy
the object.

In the programming scheme of things, this is a really big deal!

Having learned this lesson and being back working on the 400 I was
eager to use Java. Java like C# is a managed code language.  Java,
like C# works with object references that are easily returned from a
function and added to a list.

I want to use Java in place of RPG.  For green screen and sql
programming. To read and write from a display file I would use JNI to
call ILE procedures that used the "C" based recio functions to read
and write display files.  Should work great right?

Talking about this with the Java guru where I am working I am told it
cant be done. Java on the 400 is multithreaded.  The interactive
subsystem and display file i/o on the 400, either by design or because
or operating system bugs, cannot be used in a multithreaded setting. 
Hence, Java cannot be used, no way no how, for display file
programming on the 400.  Is this correct?

-Steve