Design Principles & Practices

Emerging .NET Devs October User Group Meeting

Adil Ahmed Mughal Zubair Ahmed

Refactoring to SOLID Code

Emerging .NET Devs

Session => Refactoring to SOLID Code

Sponsors:

What You must already know: - Object Oriented Programming Language such as Java, C++, C# - Professional Experience

What You will learn today: - Good Practices - OO Principles

Speaker => Adil Ahmed Mughal Affiliations:

Contact Information:

@adilamughal

http://www.adilmughal.com

adil.mughal@live.com

Agenda

This is not a single side talk, its discussion!

Promise me that you will raise hand when you have query?

• How You Code Today?

• What is Bad Design?

• What would You Call a Good Design?

• SOLID Principles!

How You Code Today?

• Do you care about design principles or patterns?

• Anti-patterns?

• Is your code Agile?

• Do you Refactor your code?

• Is your code design bad or good?

Bad design is...

Rigid

Fragile

Immobile

Viscous

Needless Complexity

Needless Repetition

What would You Call a Good Design?

• Reliability

• Flexibility

• Separations of Concerns

• Reusability

• Maintainability

SOLID

Object Oriented Principles Introduced by Robert C. Martin in

early 2000s

SOLID Principles

• S – Single Responsibility Principle (SRP)

• O – Open Closed Principle (OCP)

• L – Liskov Substitution Principle (LSP)

• I – Interface Segregation Principle (ISP)

• D – Dependency Inversion Principle (DIP)

Single Responsibility Principle (SRP)

The Single Responsibility Principle

"A responsibility is a reason to change, a class or module should have one, and only one, reason to change."

The Single Responsibility Principle

• “There should never be more than one reason for a class to change.”

• More responsibilities => More likelihood of change

• Dijkstra’s SoC: separation of concerns

• Applies on every level of code

• Solves the naming dilemma

Trade Validator

Trade Validator

Trade DB

What is wrong here: Changes if DB changes or Business Logic Changes

Refactored Trade Validator

Trade Validator

Trade

DB

Trade Source

What's its job? Classes must have an identifiable single responsibility.

The Open-Closed Principle (OCP)

The Open Closed Principle

“Software Entities (Classes, Modules, Functions, etc.) should be open for extension, but closed for modification”

The Open Closed Principle

• Modules that conform to the open-closed principle have

two primary attributes

– Open For Extension

• behavior of the module can be extended

– Closed for Modification

• The source code of such a module is inviolate

• The normal way to extend the behavior of a module is to

make changes to that module. How can these two opposing attributes be resolved?

OCP – Change behavior without changing code?

• Abstraction is the key to achieve it

Server Client

Closed Client

OCP – Change behavior without changing code?

Abstract Server

Client

Open Client

Server

Liskov Substitution Principle (LSP)

Liskov Substitution Principle

“Functions that reference a base class must be able to use objects of derived classes without knowing it."

Interface Segregation Principle (ISP)

Interface Segregation Principle

“Clients should not be forced to depend upon interfaces that they do not use.”

• Prefer small, cohesive interfaces to fat interfaces

Dependency Inversion Principle (DIP)

Dependency Inversion Principle

“High level modules should not depend upon low level modules. Both should depend upon abstractions. “

“Abstractions should not depend upon details. Details should depend upon abstractions.”

Trade Validator

Trade Validator

Trade DB

Trade Source

High Level (Less Stable)

Low Level (More Stable)

Introduce stability with abstraction

Better Trade Validator

Trade Validator

Trade

DB

DbTradeSource

<Interface> ITradeSource

Extensible Trade Validator

TradeValidator

Trade

DB

DbTradeSource

<Interface> ITradeSource

WSTradeSource

Cloud

DEMO

Let’s Refactor!

Actions => From Now On

Books:

Learn, Practice and Make it your Habit

Links:

- ObjectMentor.com - Practices and Patterns on MSDN

References

• Combatting Software Entropy using Design Principles

and Practices – Hammad Rajjoub – TechEd ME

• Agile Principles, Patterns and Practices using C# by

Robert.C.Martin

• Special thanks for motivational poster images by

NimblePros

Thank You!

Refactoring to SOLID Code

Emerging .NET Devs