public final class ExpandedDataStruct
extends SimpleDataStruct

This data structure contains the SimpleDataStruct as super class. In C the struct is defined as:

 typedef struct ExpandedDataStruct_Test_t
 { 
   union { ExpandableDataStruct_Test_s super;} base; 
   double e;
   double f;
 } ExpandedDataStruct_Test_s;

The superclass is wrapped with an union, because the access is written anytime ref.base.super, but the union doesn't contain an element ObjectJc object here. That is because the base class in not based on ObjectJc.