Polymorphism 

OOPs revolve around the four concepts:

1. Encapsulation
2. Polymorphism
3. Abstraction
4. Inheritance

In OOPs, these concepts are implemented through a class definition and achieved through the object creation process, programmatically.

Here we will discuss Polymorphism briefly:

-- Polymorphism is the ability of objects (of different types) to respond uniformly to achieve specific behavior to method calls of the same name.
-- Polymorphism does not allow the external user to be aware about the internal processing of the system, rather it allows to use the different mechanism of same name to be collected together and react appropriately to the supplied parameters to generate the desired output.
-- With Polymorphism the user does not have to know the exact type of the object in advance, as the required behavior is implemented at request processing time.
-- Polymorphism can be achieved at the run time execution and in most cases it is achieved at the compilation time also. 

Read more at :

www.roseindia.net/java/beginners/oop-in-java.shtml