OOP_Notes

Object Oriented Programming

OOP is a computer programming design philosophy or methodology.
It organizes and models software design around data, or objects rather than functions and logic.
OOP combines a group of data attributes with functions or methods into a unit called an object.
An object is referred to as a data field that has unique attributes (properties) and behaviors (functions, methods).
Properties are the state of the object. Behaviors are the actions our object take. Behaviors often modify the properties of object.
Pillars of OOP are abstraction, encapsulation, inheritance and polymorphism.
An object has attributes and functions.
A class is a blueprint or template of an object.

OOP allows to break the program into the small pieces. So the problems will be solved easily.
OOP systems can be easily upgraded from small to large systems.
OOP increases programmer productivity, quality of software and decreases maintenance cost.
We can build the programs from standard working modules that communicate each other, rather than having to start writing the code from scratch.
It makes large-scale applications much simpler because it's a great way to reduce dependencies.

OOP is about encapsulating mutable state and is therefore more appropriate for interactive applications, GUI's and API's exposing mutable state.
You have multiple programmers who don't need to understand each component.
There is a lot of code that could be shared and reused
The project is expected to change often and be added to over time
Different sections can benefit from different resources like data source and hardware.

In OOP when we model a problem in terms of objects we create abstract definitions representing the types of object we want to have in our system.
For example if we were modeling a school, we might want to have objects representing professors. Every professor has some properties in common: they all have name and a subject they teach. Also every professor can do certain things. For example they can all grade a paper and they can introduce themselves to their students at the start of the year.
So Professor could be a class in our system and the definition of the class lists data(attributes, properties) and methods that every professor has.
In pseudocode a Professor class could be written like this


xxxxxxxxxx
class Professor
    properties:
        name
        teaches
    methods:
        grade(paper)
        introduce_self()

On its own, a class doesn't do anything. It's kind of template(blueprint) for creating concrete objects of that type.
Each concrete professor we create is called instance of Professor class.
An object is referred to as an instance of the class
The process of creating an instance is performed by a special function called a constructor.

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