OOP concept

 OOP Concept

1) Class

•  The entire set of data, and code of an object can be made a user-defined data type with the help of a class.

•  In fact, Object are the variables of the type class.
•  Once a class has been defined , we can create number of objects belonging to that class.

•  Each object is associated with the data of type class with which they are created.
•  So, class is a collection of objects of similar type.
• For example, mango, apple & banana are members of class fruit.
•  Classes are user-defined data types & behave like the built-in types of a programming language.
• The syntax of creating an object is no different than the syntax used to create an integer object in c.
•  If fruit has been defined as a class, then the statement fruit mango;
•  It will create an object mango belonging to the class fruit.

2) Object

•  Objects are the basic run-time entities in the object oriented system.
•  They may represent a person, a place, a table of data, a bank account or any item that a program has to handle.
•  They also represent user define data.
•  When a program is executed, the objects interact by sending messages to one another.
•  For example if “customer” and “account” are two objects in a program then the customer object may send a message to the account object requesting for the bank balance.
• Each object contains data, code and code to manipulate that data.

3) Encapsulation

•  The wrapping up of data & functions into a single unit is known as encapsulation.
•  Data encapsulation is the most striking feature of a class.
•  The data is not accessible to the outside world & only those functions which are wrapped in the class can access it.
•  These functions provide the interface between the data of object & the program.
•  This insulation of the data from direct access by the program is called data hiding or information hiding.
•  Abstraction refers to the act of representing essential features without including the background details or explanations.
•  Classes use the concept of abstraction & are defined as a list of abstract attributes such as size ,weight ,cost & functions to operate on these attributes.  They encapsulate all the essential properties of the objects that are to be created.
•  The attributes are sometimes called data members because they hold information.
•  The functions that operate on these data are sometimes called methods or member functions.
• The classes use the concept of data abstraction , they are known as Abstract Data Types (ADT).

4) Inheritance

•  Inheritance is the process by which objects of one class acquire the properties of objects of another class.

•  It supports the concept of hierarchical classification.
• For example , the bird sparrow is a part of the class “flying bird” which is again a part of the class “bird”.
•  The principle behind this sort of division is that each derived class shares common characteristics with the class from which it is derived as illustrated in fig. :1.4.
•  In OOP, the concept of inheritance provides the idea of reusability.
• This means that we can add additional features to an existing class without modifying it.
• This is possible by deriving a new class from the existing one. 
• The new class will have the combined features of both the classes.
• Note , that each sub-class defines only those features that are unique to it.
•  Without the use of classification , each class would have to explicitly include all of its features