The mapping of FML and VIEW buffers to Java data types is performed in a similar manner as that described in How Do I: Map Java Data Type Buffers to FML and VIEW. The mapping is controlled by the fields or data members of the objects specified as the method's return type and not by the fields in the FML or VIEW buffer. Each field in the return type is retrieved from the FML or VIEW buffer based on matching the object's field name to the FML field name or VIEW class. The return type must be an instantiable type, a class not an interface or even abstract class. The control uses that return type as the type it will instantiate. Because interfaces or abstract classes cannot be instantiated, they are not allowed as the return type.