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exo3_poo

Ce 3e cours concerne l'utilisation des principes de programmation orienté objet

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Object Oriented Design

Promo#1 Simplon.VE

Avril-Octobre 2015

Sources :

Practical Object-Oriented Design in Ruby - by Sandi Metz

http://rubylearning.com/satishtalim/tutorial.html https://en.wikibooks.org/wiki/A-level_Computing/AQA/Problem_Solving,_Programming,_Operating_Systems,_Databases_and_Networking/Programming_Concepts/Object-oriented_programming_(OOP) https://robots.thoughtbot.com/back-to-basics-polymorphism-and-ruby

What is OOP?

  • Object Oriented Programming
  • a design philosophy
  • everything is grouped as self sustainable "objects"

Why ?

=> to gain reusability

Example

A “hand”

The “hand” is a class. <= Abstraction here !

Your body has two objects of the type "hand" :

  • "left hand"
  • "right hand"

Functions are controlled by a set of electrical signals sent through your shoulders

Shoulder = interface

The hand class is being reused to create the left hand and the right hand by slightly changing the properties of it.

What is an Object?

A "thing" that can perform a set of related activities.

The Hand (object) can grip something,

A Student (object) can give their name or address.

An object is always an instance of a class.

What is a Class?

  • A representation of a type of object
  • A plan, or a template, that describes the details of an object.

  • A class is a template which cannot be executed
  • An object is an instance of a class which can be executed
  • one class can be used to make many objects-

Class is composed of three things:

  • a name
  • attributes
  • methods

How to identify and design a Class?

This is an art

But you have SOLID

SOLID are 5 principles that you must follow when design a class

1 SRP - The Single Responsibility Principle

A class should have one, and only one, reason to change

2 OCP - The Open Closed Principle

Should be able to extend any classes' behaviors, without modifying the classes

3 LSP - The Liskov Substitution Principle

A subclass can be used anywhere its superclass would do

4 ISP - The Interface Segregation Principle

Make fine grained interfaces that are client specific

5 DIP - The Dependency Inversion Principle

Depend on abstractions, not on concretions.

To identify a class correctly

  • identify the full list of functions
  • group each function to form classes

Divide and conquer !

Stop talking !

Show me some examples

Adavantages of SRP

  • Expose previously hidden qualities
  • Avoid the need for comments
  • Encourage reuse
  • Are easy to move to another class

Refactors are needed, not because the design is clear, but because it isn’t.

Exercice

À partir des commandes et résultats suivant, retrouver les classes à écrire.

player_1 = Player.new "Ryu"
player_2 = Player.new "Ken"

player_1.hp = 100
player_1.force = 10

player_2.hp = 200
player_2.force = 5

player_1.hit player_2
# => Ken perd 10 hp !

puts player_2.hp
# => 190

20.times do
  player_2.hit player_1
  # => Ryu perd 5 hp !
end
# => Ryu a perdu !
Object Oriented Design Promo#1 Simplon.VE Avril-Octobre 2015