CombustionTurbine and CoalFired, that extend, or inherit from class Generator. Objects of all three classes might share attributes such as the amount of power they are generating, the maximum and minimum amount of power they can generate, their fuel and operating costs, physical location, and plant name. They may also each have a method called produceElectricity whose job is to provide an electrical output. However, the definition for class CombustionTurbine’s produeeElectricity method will differ from that of class CoalFired, even though both inherit the ability to produce electricity from their common superclass, Generator. Both subclasses actually are types of generators, and so both know what it means to produce electricity, However, they do so in different ways. Again this sort of relationship, in which types of objects exhibit similar sets of behaviors but act in different ways, very closely parallels physical reality.