Features and characteristics of OOP

Object oriented programming (OOP) is a programming approach that organises a program as a collection of objects, where each object bundles data and the functions that work on that data. The main features are:

1. Objects and classes - An object is a real-world entity with state (data) and behaviour (functions), such as a student or a bank account. A class is the blueprint from which objects are created; it is a user-defined data type.
2. Data abstraction - Showing only the essential features to the user and hiding the implementation details. A user calls withdraw() without knowing how the balance is updated.
3. Encapsulation - Wrapping data and functions into a single unit (the class). Data is kept private and is reached only through public member functions, which gives data hiding and protects data from accidental change.
4. Inheritance - A new (derived) class acquires the properties and behaviour of an existing (base) class. It supports code reuse and a hierarchy of classes, e.g. Student derived from Person.
5. Polymorphism - "One name, many forms". The same function name or operator behaves differently in different situations. It is of two kinds:
   • compile-time: function overloading and operator overloading
   • run-time: virtual functions
6. Dynamic binding - The code executed for a function call is decided at run time, not at compile time. It goes with polymorphism and virtual functions.
7. Message passing - Objects communicate by sending messages, i.e. calling the member functions of other objects: object.function(arguments).

   Person (base)
      ^
      |  inheritance
   Student (derived)

Example: In a banking program, Account is a class; ram and sita are its objects. Balance is private (encapsulation), and Saving and Current accounts inherit from Account.

These features make programs more secure, reusable, and easier to maintain.