I am not sure what you are trying to do here, but I can tell you why it is calling the default constructor. You have a class RMIClient which is Serializable, but it extends a class (Data) which is not. When the
Java de-serializes an object it will attempt to call default constructors on any super classes which are not serializable. Basicly, for a class to be serializable there are restrictions on its memember variables (they must be primitives, transitive, or implement serilaizable) and there are restrictions on the super class. It must be serializable or have a default constructor.
I somewhat doubt if you want to make Data serializable, so you likly want to re-think your design.