Polymorphism is a Greek word that literally means many shapes. Although polymorphism is tightly coupled to inheritance, it is often cited separately as one of the most powerful advantages to object-oriented technologies. When a message is sent to an object, the object must have a method defined to respond to that message. In an inheritance hierarchy, all subclasses inherit the interfaces from their superclass. However, because each subclass is a separate entity, each might require a separate response to the same message.

For example, consider the Shape class and the behavior called Draw. When you tell somebody to draw a shape, the first question asked is, “What shape?” No one can draw a shape, because it is an abstract concept (in ...

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