Object Oriented Programming

Object - Is data grouped with it’s methods.

Class -  Is the framework of an object.  There are two levels to an object, the object itself and it’s class instance, with data and methods possible at each level.

Interface -  Is the contract that an object has with it’s callers.

Package -  A code module, with it’s own name space

Inheritance -  The way you can reuse an existing class while extending it’s functionality for a more specific case.

Encapsulation - not allowing anything outside the objects methods direct access too an objects data.

Basically with object oriented programming you create an interface that groups functions, state and data together as a single unit.  The interface should do only one thing, but should do it well.  Since the interface is very simple and is only performing a fixed set of functions it is easy to test the interface, and to reuse the interface in other places.