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The Single Responsibility Principle (SRP) is one of the 5 SOLID principles. These slides gives you an overview of the principle as well as a refactoring from a non-SRP code to a SRP-code.
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The Single Responsibility Principle
Lars-Erik KindbladSenior Consultant
Blog: kindblad.com
Agenda
What is the Single Responsibility Principle?Code SampleSummary
Single Responsibility Principle
Single Responsibility Principle = SRP1 of the 5 SOLID principles for creating better object-oriented code
The Single Responsibility Principle The Open Closed Principle The Liskov Substitution Principle The Interface Segregation Principle The Dependency Inversion Principle
SRP states that ”a class or module should have one, and only one, reason to change” A class should do one thing A class should have only one responsibility
The benefit: smaller classes that are easier to read, maintain and unit-test
The God Object
A God object is an object that knows too much or does too muchThe opposite of the SRP
CODE SAMPLE
Database code
Send mail code
1. Extract mail sending code
2. Extract database code
Repositories are potential God-objects
3. Replace Repository.GetUser with a DbCommand
4. Replace Repository.AddUser with a DbCommand
5. Replace Repository.DeleteUser with a DbCommand
UserManager looks like a facade class
... Extract
6. Extract RegisterUser
7. Rename UserManager
... to UserFacade
Not every dependency are needed at all times
8. Change to a Service Locator
9. Validation
Could be extracted but not needed now since the class
is small...
Overview
AddUserDbCommand
DeleteUserDbCommand
GetUserDbCommand
SendEmailConfirmationRegisterUser
UserFacade
Remove?
Summary
A class following the single responsibility principle is a class that does only one thing and has only one reason to change
The opposite of SRP is a God-objectBenefits
Easy to give the class a good name Less code per class means reduced complexity, less errors, easier to maintain, extend
and test
Arguments against Too many classes Difficult to understand the big picture
The pros outweights the cons – SRP is a requirement forwriting maintainable unit-tests
QUESTIONS?
The information contained in this presentation is proprietary.© 2012 Capgemini. All rights reserved.
www.capgemini.com
About Capgemini
With more than 120,000 people in 40 countries, Capgemini is one of the world's foremost providers of consulting, technology and outsourcing services. The Group reported 2011 global revenues of EUR 9.7 billion.Together with its clients, Capgemini creates and delivers business and technology solutions that fit their needs and drive the results they want. A deeply multicultural organization, Capgemini has developed its own way of working, the Collaborative Business ExperienceTM, and draws on Rightshore ®, its worldwide delivery model.
Rightshore® is a trademark belonging to Capgemini
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