C++ Pillars of OOP

Pillars of Object Oriented Programming

The features which make the language ‘Object Oriented Language’, are called the Pillars of Object Oriented Programming.

Pillars Of Object Oriented Programming

Pillars Of Object Oriented Programming

Major Pillars

1 Abstraction

  • Getting only essential things and hiding unnecessary details is called abstraction.
  • It is the public access region of the class.
  • Generally, it declares the operations that can be invoked by the clients on object of class.
  • Avoid using data members in public region of class, as it may be directly changes by the client.
Abstraction in c++

Example of Abstraction in c++

2 Encapsulation

  • Binding of data and code together is called encapsulation.
  • Encapsulation maintains integrity of object.
  • For example, the Man class has a walk() method. The code for the Walk() method defines exactly how a walk happens.
  • The encapsulation is most often achieved through information hiding.
  • Information hiding is the process of hiding all the secrets of an object that do not contribute to its essential characteristics; typically,structure of an object is hidden, as well as implementation of its methods.

3 Modularity

  • The act of portioning a program into individual components can reduce its complexity to some degree.
  • Modularity can be physical modularity(e.g. divide program into .h, .cpp, .rc files) or logical modularity(e.g. namespace)
  • Modularization consists of dividing program into modules that can be compiled seperately, but which are interconnected.
  • Modularity helps in easier maintenance of a complex software.

4 Hierarchy

Hierarchy is ranking or ordering of abstractions.
Main purpose of hierarchy is to achieve re-usability.
The hierarchies are:
1. Inheritance (is-a relationship):

Acquiring all the properties(data members) and behaviors of one class by another class is called inheritance.

Class Diagram-Inheritance

Class Diagram-Inheritance

2. Composition (has-a relationship):

When object is madhe from other small objects it is called composition.

Class Diagram-Composition

Class Diagram-Composition

A is owner of B and B is non shareable.

3. Aggregation (has-a relationship):

Class Diagram-Aggregation

Class Diagram-Aggregation

A has B, A is owner of B, and B is shareable.

4. Aggregation (work-for relationship):

  • Two objects works together for long time.
  • It is bidirectional relationship
  • In association, both are independent entities but just working together for long duration.
Class Diagram-Association

Class Diagram-Association

5. Dependency (use-a relationship):

  • Sometimes the relationship between two classes is very weak.
  • They are not implemented with member variables at all.
  • Rather they might be implemented as member function arguments.
Class Diagram-Dependency

Class Diagram-Dependency


It is Greek word which is a combination of poly(many) + morphism(forms/behavior).
One interface having many behaviors such phenomenon is called polymorphism.

Types of polymorphism:

1. Compile time polymorphism:

  • It is also called as static polymorphism, false polymorphism, early binding.
  • When call to functions is resolved at compile time it is called compile time polymorphism.
  • In c++, Compile time polymorphism is achieved by using function overloading and operator overloading.

2. Run time polymorphism:

  • It is also called as dynamic polymorphism, true polymorphism or late binding.
  • When call to the function resolved at run time, it is called run time polymorphism.
  • In c++, run time polymorphism is achieved by using function overriding.

Minor Pillars

1 Concurrency

  • The concurrency problem arises when multiple threads simultaneously access same object.
  • We may use a class library for providing threading support.
  • We may use interrupts to give illusion of concurrency which need hardware details.
  • You need to take care of object synchronization when concurrency is introduced in the system.

2 Persistence

  • It is property by which object maintains its state across time and space.
  • The concept gives rise to the concept of object oriented database.
  • It talks about concept of serialization and also about transferring object across network.