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TRANSCRIPT
SOLID
WHAT’S HE GONNA TALK ABOUT
What is SOLID The S in SOLID The O in SOLID The L in SOLID The I in SOLID The D in SOLID Questions
WHAT’S THIS SOLID BUSINESS
SOLID Principles
Object-Oriented Design
En
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lati
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Inh
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Poly
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WHAT’S THIS SOLID BUSINESS
A means to avoid technical debt Decrease Coupling Increase Cohesion
Maintainable Extensible Testable
WHAT’S THIS SOLID BUSINESS
Guidelines, NOT LAWS
You got to know when to hold’em, know when to fold’em,
Know when to walk away and know when to run.-Kenny Rogers
THE REQUEST 1
Application
Flat File
EmailSender•SendEmail•GetMessage
Single Responsibility Principle
SRP
There should never be more than one reason for a class to change
-Uncle Bob
SINGLE RESPONSIBILITY PRINCIPLE
VIOLATES THE PRINCIPLE ABIDES BY THE PRINCIPLE
Application
Flat File
EmailSender•SendEmail•GetMessage
Application
Flat File
FileReader•GetMessage
EmailSender•SendEmail
A REQUEST 2
Application
Flat File
FileReader•GetMessage
EmailSender•SendEmail
XML File
Open-Close Principle
OCP
Software entities (classes, modules, functions, etc…) should be open for extension, but closed for modification
-Uncle Bob
OPEN-CLOSED PRINCIPLE
VIOLATES THE PRINCIPLE ABIDES BY THE PRINCIPLE
Application
Flat File
FileReader
•GetMessage
EmailSender
•SendEmail
XML File
Application
Flat File
BaseFileTypeReader
•CanRead•ReadFile
EmailSender
•SendEmail
XML File
FlatFileReader
•CanRead•ReadFile
XmlFileReader
•CanRead•ReadFile
FileReader
•GetMessage•RegisterDefaultFileTypeReader•RegisterFileTypeReader
REQUEST 3Application
Flat File
BaseFileTypeReader
•CanRead•ReadFile
EmailSender
•SendEmail
XML File
FlatFileReader
•CanRead•ReadFile
XmlFileReader
•CanRead•ReadFile
FileReader
•GetMessage•RegisterDefaultFileTypeReader•RegisterFileTypeReader
DB File
DbFileReader
•CanRead•ReadFile
Database
Liskov Substitution Principle
LSP
Functions that use pointers or references to base classes must be able to use objects of derived classes without knowing it
-Uncle Bob
LISKOV SUBSTITUTION PRINCIPLE
VIOLATES THE PRINCIPLE ABIDES BY THE PRINCIPLE
Application
Flat File
BaseFileTypeReader
•CanRead•ReadFile
EmailSender
•SendEmail
XML File
FlatFileReader
•CanRead•ReadFile
XmlFileReader
•CanRead•ReadFile
FileReader
•GetMessage•RegisterDefaultFileTypeReader•RegisterFileTypeReader
DB File
DbFileReader
•CanRead•ReadFile
Database
Application
Flat File
BaseFileTypeReader
•CanRead•ReadFile
EmailSender
•SendEmail
XML File
FlatFileReader
•CanRead•ReadFile
XmlFileReader
•CanRead•ReadFile
FileReader
•GetMessage•RegisterDefaultFileTypeReader•RegisterFileTypeReader
DbReader
•GetMessage
Database
REQUEST 4Application
Flat File
BaseFileTypeReader
•CanRead•ReadFile
EmailSender
•SendEmail
XML File
FlatFileReader
•CanRead•ReadFile
XmlFileReader
•CanRead•ReadFile
FileReader
•GetMessage•RegisterDefaultFileTypeReader•RegisterFileTypeReader
Database
IReader
•GetMessage•RegisterDefaultFileTypeReader•RegisterFileTypeReader
DbReader
•GetMessage•RegisterDefaultFileTypeReader•RegisterFileTypeReader
Interface Segregation Principle
ISP
Clients should not be forced to depend upon interfaces that they do not use
-Uncle Bob
INTERFACE SEGREGATION PRINCIPLE
ABIDES BY THE PRINCIPLE
Application
Flat File
BaseFileTypeReader
•CanRead•ReadFile
EmailSender
•SendEmail
XML File
FlatFileReader
•CanRead•ReadFile
XmlFileReader
•CanRead•ReadFile
FileReader
•GetMessage•RegisterDefaultFileTypeReader•RegisterFileTypeReader
Database
IReader
•GetMessage
DbReader
•GetMessage
IFileTypeReaderRegisterable
•RegisterDefaultFileTypeReader•RegisterFileTypeReader
Dependency Inversion Principle
DIP
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
-Uncle Bob
DEPENDENCY INVERSION PRINCIPLE
ABIDES BY THE PRINCIPLE
Application
Flat File
BaseFileTypeReader
•CanRead•ReadFile
IEmailSender
•SendEmail
XML File
FlatFileReader
•CanRead•ReadFile
XmlFileReader
•CanRead•ReadFile
FileReader
•GetMessage•RegisterDefaultFileTypeReader•RegisterFileTypeReader
Database
IReader
•GetMessage
DbReader
•GetMessage
IFileTypeReaderRegisterable
•RegisterDefaultFileTypeReader•RegisterFileTypeReader
EmailSender
•SendEmail
WITHOUT SOLID
Application
Flat File
EmailSender•SendEmail•GetMessage
Xml File
Database
WITH SOLID
Application
Flat File
BaseFileTypeReader
•CanRead•ReadFile
IEmailSender
•SendEmail
XML File
FlatFileReader
•CanRead•ReadFile
XmlFileReader
•CanRead•ReadFile
FileReader
•GetMessage•RegisterDefaultFileTypeReader•RegisterFileTypeReader
Database
IReader
•GetMessage
DbReader
•GetMessage
IFileTypeReaderRegisterable
•RegisterDefaultFileTypeReader•RegisterFileTypeReader
EmailSender
•SendEmail
QUESTIONS?
REFERENCE LINKS
Martin Folwer – Technical Debt http://www.martinfowler.com/bliki/TechnicalDebt.html
Wikipedia – Coupling http://en.wikipedia.org/wiki/Coupling_(computer_programmi
ng) Wikipedia – Cohesion
http://en.wikipedia.org/wiki/Cohesion_(computer_science) Robert Martin – The Principles of OOD
http://butunclebob.com/ArticleS.UncleBob.PrinciplesOfOod Derick Bailey – SOLID Principles – Step by step code
https://github.com/derickbailey/presentations-and-training/tree/master/SOLID%20Principles%20-%20Step%20By%20Step%20Code
MY INFORMATION
Email – [email protected] Twitter – @tonycwang LinkedIn –
www.linkedin.com/in/tonycwang