10.6. Polymorphism and Inheritance

In Java, the type of a variable does not determine the type of the object to which it refers. For example, a variable of type BankAccount can hold a reference to an actual BankAccount object or a subclass object such as SavingsAccount. You already encountered this phenomenon in Chapter 9 with variables whose type was an interface. A variable whose type is Measurable holds a reference to an object of a class that implements the Measurable interface, perhaps a Coin object or an object of an entirely different class.

What happens when you invoke a method on a variable of type BankAccount? For example,