Pillars of Object Oriented Programming

Pillars of Object Oriented Programming

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

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.

2. Composition (has-a relationship):

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

A is owner of B and B is non shareable.

3. Aggregation (has-a relationship):

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.

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.

Polymorphism

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.