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A  class can inherit characteristics from another class .Classes em¬body coherent and cohesive concepts. Classes can be used to create more specialized Classes via inheritance. For example, a bicycle can be specialized to a kind built by a given manufacturer.
Inheritance is the mechanism that allows the programmer to derive new classes from existing classes. The derived classes inherit the methods and data structures of the parent class. One can add new methods or override the inherited methods to make them more specific. The parent methods will not be affected because of these modifications.
For example, different kinds of bicycles like bikes can inherit the common properties from a bicycle class and can override the methods in the parent class to suit local properties. For example, some racing bikes have an extra set of gears with a lower gear ratio.

Polymorphism
Polymorphism is a feature that allows one interface to be used for a general class of actions. The concept of polymorphism is often ex-pressed by the phrase “one interface, multiple methods”. It basi¬cally refers to the ability of giving the same name to methods in different subclasses. The individual methods may implement simi¬lar tasks but can be differentiated by the type of arguments passed to them.
By using polymorphism different methods can be created with the same name but with different parameters.

One of the fundamental principles of object technology is that the internals of an object are private to that object and may not be accessed or even examined from outside the object.
Encapsulation is a simple yet reasonably effective building tool. It is a way of packaging information. Encapsulation allows the pro-grammer to present clearly specified interfaces around the services they provide. The programmer can decide what should be hidden and what is intended to be visible.
Some advantages of encapsulation are:
•    Managing complexity
•    Managing change
•    Protecting data
Message    :   The communication media of objects.
Subclass    :   A class inheriting another class’s properties.
Data hiding : Protecting data by preventing direct access to it. This is done by making the data, private or pro¬tected members of a class.
Abstraction
Abstraction refers to the act of representing essential features with¬out including the background details or explanations. It is the art of concentrating on the essential thing and ignoring the non-essential things.
Classes that use the concept of data abstraction are known as “abstract data types”. Abstract data types are achieved by making certain variables and methods in a class as private. Abstraction makes an objects look either unique, similar to or different from other objects depending on viewers.
For example, people do not think of a computer as a set of thousands of individual parts. They can ignore the details of how the CPU, Monitor and Keyboard works.

Some of the buzzwords in object oriented programming are
•    Objects
•    Classes
•    Encapsulation
•    Abstraction
•    Inheritance
•    Polymorphism
Objects
An object is a concrete instance of some classes. Objects are the basic entities in an object-oriented system. Each object is denoted by a name and has a state. The variables within the object express everything about the object(state) and the methods Specify how it can be used (behavior). For example, a bicycle has a state (the number of wheels and the current gear), and behavior (breaking, accelerat¬ing, slowing down, changing gears).
Method
A method is a function or a procedure that access to the internal state of the object needed to perform some operation. So, methods are functions defined inside the classes that operate on instances of those classes
Classes
A class is a blueprint or a prototype that defines the variables(data) and methods (code) common to all objects of certain kind. The class serves as a user-defined type. A class thus defines a data type that behaves like the built-in types of a programming language. An ob¬ject is an individual instance of a class.
Access to the variables and methods declared in a class depend on whether they are declared in private or public. A variable declared as public is visible everywhere. A variable declared as private is not visible outside the class.

Introduction
Object oriented programming focuses on defining a hierarchy of classes of objects, each with associated data fields and methods. Subclasses inherit data fields and methods from their parent and ancestor classes.
Object oriented programming is generally considered good for software re-use and maintenance as objects, with clearly defined interfaces can be used and modified with relatively little effort. It has been widely used in creating user interface libraries and toolkits.
Object Oriented Programming
OOP is a programming language that is based on the Object Orientation methodology. The major advantages of OOP is its capabilities for creating flexible, modular programs and its abilities of code reuse.
Object orientation provides a new paradigm for software con-struction. In this new paradigm, objects and classes are the build¬ing blocks, while methods, messages and inheritance produce the primary mechanisms
Object-oriented programming is a programming method that combines data and instructions into a self-sufficient “object”. In an object-oriented program, the design is represented by objects. Objects

Usenet, which is short for Users Network, is an international net¬work of newsgroups. With an estimated 15-20 million frequent us¬ers on Usenet, even the most unusual and specific newsgroups seem to never run out of messages. The fact that Usenet is such a large network is what makes it so valuable. Usenet can be useful in many ways. The most obvious use in as an information resource. No mat¬ter how unusual a question, there is probably a newsgroup out there with enough people who would be willing and able to give we an answer. Although some of the answers might not be completely accurate, we usually will receive enough replies that we will be able to weed out the incorrect responses. In addition to getting our ques¬tions answered, Usenet can also be used as a news source. There are dozens of newsgroups devoted to the discussion of current events in countries around the world. Until recent years, Usenet has fo¬cused primarily on computer-based topics or technical discussions. But, with the sudden increase in Internet users outside the techni¬cal professions, a Usenet has softened up quite a bit and now in-cludes hundreds of newsgroups for the discussion of the fine arts (such as music, paintings, or theater), as well as other non-compu¬ter topics like gardening, sports, TV, and clothing.