Answer Posted / vamsi krishna srirangam

upcasting is used to acess the common methods of
subclass(which are redefined from super class) using super
class reference.
use:because of this only polymorphism is possible.
example:
lcl_truck,lcl_bus are subclasses to lcl_vehicle

vehicle_list type table of ref to lcl_vehicle.

lcl_vehicle = lcl_truck.
append lcl_vehicle to vehicle_list.
clear lcl_vehicle.

lcl_vehicle = lcl_bus.
append lcl_vehicle to vehicle_list.
clear lcl_vehicle.
now if you redefine the estimate_fuel method in each
subclass then that particular method only called because
fuel estimation is different for bus and truck.

Down-casting:
to take control back to the object that is called now.
to identify the triggered subclass object from the list of
available subclass objects.

?= means check whether the reference(path)
is same. if left hand path is equals to right hand path then
it copies the right hand path to left hand variable.
it is used to pick one from several

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