Java: Upcasting and Dynamic Dispatch

Upcasting hides subclass-specific methods.

When upcasting, the reference type restricts access to only those methods declared in the superclass, even though the actual object might have more specialized methods. This is because the compiler only recognizes methods available in the reference type. For example, if `Book` has a method `read()`, it won't be accessible through a `Product` reference after upcasting.