Object Oriented ABAP

obj_a = obj_b1.
Then both obj_a and obj_b now refer to same object of class b.
But obj_a is reference variable of type parent class of class b.
Now when
obj_a = obj_b .
Reference variable is of type Base Class
Object passed is of type Sub Class.
When we will use the reference variable obj_a to invoke method rise() which is overridden
in sub class b, the sub class b method rise() (redefined method) is invoked.
So if we change the code below START-OF-SELECTION event and END-OF-SELECTION event
in section 2.1 to check the above theory.
*****************************************************************
* START-OF-SELECTION
******************************************************************
START-OF-SELECTION.
create object : obj_a,
obj_b1,
obj_b2.
obj_a = obj_b1.
*****************************************************************
* END-OF-SELECTION
******************************************************************
END-OF-SELECTION.
call method : obj_a->fall,
obj_a->rise,
obj_b1->fall.
Now output of above code is :
Super class a-----------fall()
Child class b redefined-----------rise()
Super class a-----------fall()