The mechanism by which the data and functions are bound together into a single unit is known as Encapsulation. Encapsulation is the most striking feature of a class. The data is not accessible to the outside world, and only those functions which are wrapped in the class can access it. These functions provide the interface between the object's data and the program. This encapsulation of data from direct access by the program is called data hiding or information hiding.

Objects:
Represents data and its associated function together into a single unit. Objects are the basic unit of OOP. Basically an object is created from a class. They are instances of class also called as class variables. An identifiable entity with some characteristics and behaviour is called object.

Modularization: where the program can be decomposed into modules.
Software re-use: where a program can be composed from existing and new modules.

Important features of Modular programming:
1. Emphasis on algorithm rather than data
2. Programs are divided into individual modules
3. Each modules are independent of each other and have their own local data
4. Modules can work with its own data as well as with the data passed to it.
Example: Pascal and C.

1. Programs are organized in the form of subroutines or sub programs.
2. All data items are global.
3. Suitable for small sized software application.
4. Difficult to maintain and enhance the program code as any change in data type needs to be propagated to all subroutines that use the same data type. This is time consuming.
Example: FORTRAN and COBAL.

Advantages of OOP:
(i) Re-usability: Write once and use it multiple times you can achieve this by using class.
(ii) Redundancy: Inheritance is the good feature for data redundancy. If you need a same functionability in multiple class you can write a common class for the same functionality and inherit that class to sub class.
(iii) Easy Maintenance: It is easy to maintain and modify existing code as new objects can be created with small difference to existing ones.
(iv) Security: Using data hiding and abstraction only necessary data will be provided thus maintains the security of data.
Disadvantages of OOP:
(i) Size: Object Oriented Programs are much larger than other programs.
(ii) Effort: Object Oriented Programs require a lot of work to create.
(iii) Speed: Object Oriented Programs are slower than other programs, because of their size

(i) The mechanism by which the data and functions are bound together into a single unit is known as ENCAPSULATION. It implements abstraction.
(ii) Abstraction refers to showing only the essential features without revealing background details.
(iii) Modularity is designing a system that is divided into a set of functional units that can be composed into a larger application.
(iv) Polymorphims is the ability of a message or function to be displayed in more than one form.
(v) Inheritance is the technique of building new classes (derived class) from an existing class.
(vi) The most important advantage of inheritance is code reusability.
(vii) Inheritance is transitive in nature.

The Object Oriented Programming has been developed to overcome the drawbacks of procedural and modular programming. It is widely accepted that object-oriented programming is the most important and powerful way of creating software.
The Object-Oriented Programming approach mainly encourages:
1. Modularization: where the program can be decomposed into modules.
2. Software re-use: where a program can be composed from existing and new modules.
Main Features of Object Oriented Programming
1. Data Abstraction
2. Encapsulation
3. Modularity
4. Inheritance
5. Polymorphism
Encapsulation
The mechanism by which the data and functions are bound together into a single unit is known as Encapsulation. It implements abstraction.
Encapsulation is about binding the data variables and functions together in class, It can also be called data binding.
Encapsulation is the most striking feature of a class. The data is not accessible to the outside world, and only those functions which are wrapped in the class can access it. These functions provide the interface between the object's data and the program. This encapsulation of data from direct access by the program is called data hiding or information hiding.
Classes use the concept of abstraction to define a list of abstract attributes and function which operate on these attributes. They encapsulate all the essential properties of the object that are to be created. The attributes are called data members because they hold information. The functions that operate on these data are called methods or member function.
Modularity
Modularity is designing a system that is divided into a set of functional units (named modules) that can be composed into a larger application.
Inheritance
Inheritance is the technique of building new classes (derived class) from an existing Class (base class). The most important advantage of inheritance is code reusability.
Polymorphism
Polymorphism is the ability of a message or function to be displayed in more than one form.

Re-usability: "Write once and use it multiple times" you can achieve this by using class.
Redundancy: Inheritance is the good feature for data redundancy, If you need a same functionality in multiple class you can write a common class for the same functionality and inherit that class to sub class.
Easy Maintenance: It is easy to maintain and modify existing code as new objects can be created with small difference to existing ones.
Security: Using data hinding and abstraction only necessary data will be provided thus maintains the security of data.

Main Features of Object Oriented Programming:
1. Data Abstraction
2. Encapsulation
3. Modularity
4. Inheritance
5. Polymorphism

Inheritance is the technique of building new classes (derived class) from an existing Class (base class). The most important advantage of inheritance is code reusability.

Modularity is designing a system that is divided into a set of functional units (named modules) that can be composed into a larger application.

An identifiable entity with some characteristics and behaviour is called object

It can also be defined as a template or blueprint representing a group objects that share common properties and relationship.