Java FAQ 2 - What is Polymorphism?
Polymorphism is a way for an object of an abstract class to gain the methods and variables of another class that is not abstract. The non-abstract class must have methods for all of the abstract methods of the abstract class. Let’s revisit the Vehicle example from the Inheritance FAQ. While the subclasses inherited methods and variables from the superclass in that example, in this example, an object of the abstract Vehicle class can receive the methods of another class, say the Sedan class. The Vehicle class in affect becomes an object of the Sedan class.The following diagram is an example of Polymorphism:
The abstract Vehicle class can receive the methods from any of these other four classes, Sedan, Coupe, SUV, and Pickup, as long as these classes have non-abstract methods for any abstract methods in the Vehicle class.