In order to make the code independent from the concrete classes (JMapper and RelationalJMapper), the framework exposes the interfaces: IJMapper and IRelationalJMapper, which respectively define the contracts for JMapper and RelationalJMapper classes.

Also you can perform mapping between raw types, operations allowed are implicit structural conversions:
ArrayList <-> Set
SortedMap <-> HashMap
List <-> Set
For JMapper is impossible to know the type of the internal objects, for this reason they must be assignables.

There are two classes that can help you in everyday situations and they are: GeneralUtility and ClassesManager, by a look.