Question:What is Upcasting  and Downcasting. 

Upcasting: An upcast operation creates a base class reference from a subclass reference.
Example:
Stock msft = new Stock();
       Asset a = msft;
Downcasting: A downcast operation creates a subclass reference from a base class reference.
Example:
Stock msft = new Stock();
       Asset a = msft;
       Stock s = (Stock)a;