Conversion Rules for References 

ABAP currently uses class and interface variables within ABAP Objects. Both are pointers to objects. You can assign values to them in the following combinations:

• If the two class references are incompatible, the class of the target field must be the predefined empty class OBJECT.
• When you assign a class reference to an interface reference, the class of the source field must implement the interface of the target field.
• If two interface references are incompatible, the interface of the target field must contain the interface of the source field as a component.
• When you assign an interface reference to a class reference, the class of the source field must be the predefined empty class OBJECT.