An object encapsulates both data and functions. Objects which share the same behavior are said to belong to the same class. All objects are instances of some class . Aid to conceptualization and abstraction. One object accesses another object by sending it a message .
Message is addressed to an object.
Inheritance Definition of a class in terms of another class. OOP allows easy re-use and extension Software reused when used as a part of software other than that for which it was initially designed. Software extended when new functionality is added to an already existing program.