Embed Size (px)
Citation preview
Single Responsibility Principle
By Eyal Golan
About Me
2
Senior Java developer and agile practitioner.Practicing TDD, clean code. Software craftsmanship advocate.
Tech lead / Scrum master @ eBayTeam lead @ StartApp, doing, among other things:● Manages the continuous integration and deployment of the system.● Leading the coding practices.
Engineering team lead @ AppLift (Berlin)
Agenda
1. SOLID
2. SRP overview
3. Why SRP?
4. Recognizing SRP violation
5. Develop for SRP
6. Summarize
3
4
•Robert C. Martin – Uncle Bob•http://en.wikipedia.org/wiki/SOLID_(object-
oriented_design)5
Single responsibility principleOpen / closed principleLiskov substitution principleInterface segregation principleDependency inversion principle
SOLID
•Single responsibility principle•A class should have only a single
responsibility
6
SOLID
•Open/closed principle•Open for extension, but closed for
modification•Alistair Cockburn: “…Identify points of predicted
variation and create a stable interface around them…”
7
SOLID
•Liskov substitution principle•Replace objects with instances of their
subtypes without altering the correctness of that program
8
Rectangle
Square
SOLID
•Interface segregation principle•Many client-specific interfaces are better
than one general-purpose interface
9
SOLID•Dependency inversion principle•Abstractions should not depend on details•Don’t depend on anything concrete
•Work with interfaces
10
11
SingleResponsibilityPrinciple
Single Responsibility Principle
•Wikipedia• …the single responsibility principle states that every class
should have a single responsibility, and that responsibility should be entirely encapsulated by the class. All its services should be narrowly aligned with that responsibility…
•Clean Code•A class or module should have one, and only
one, reason to change
12
Which Components?
•Methods•Classes•Packages•Modules•System
13
14
Why SRP ?
Why SRP?
•Organize the code
15
George A. Miller
Why SRP?
• A place for everything and everything in its place
16
Why SRP?
•Less fragile code
•Low coupling
•High cohesion
17
Why SRP?
•Easier code changes (Refactoring)
18
Why SRP?
•Easier naming•The smaller and more focused class, it will
be easier to name
19
Why SRP?
•Maintainability
•Testability and easier debugging
20
21
RecognizingSRPViolation
Recognizing By Structure
•Class / method is too long
22
Class:
LOC > 250
Bad
Recognizing By Structure
•Too many dependencies (fields / parameters)
23
ClassDependency 1
Dependency 2
Dependency 3
Dependency 4
Dependency 5
Dependency 6
Recognizing By Structure
•Low cohesion
24
Recognizing By Structure
•Description / name needs: “AND”
•Generic name: “EmployeeManager”
25
void calculateAndSend(…)
Recognizing By Structure
•A method with many levels
26
if
while
Recognizing By Behavior
•Class needs to be changed for more than one behavioral change
27
Recognizing By Behavior
•Complicated test
28
when(…).then(…); when(…).then(…);
when(…).then(…);
when(…).then(…);when(…).then(…);
when(…).then(…);
Recognizing By Behavior
•Change here, break there
•Test may be broken elsewhere
•The “shotgun effect”
29
Recognizing By Behavior
•Unable to encapsulate the module
30
31
Develop ForSRP
Develop for SRP
•Awareness•The state or ability to perceive, to feel, or to
be conscious of events, objects, or sensory patterns
32
Develop for SRP
•Testable code
•TDD
33
Test
CodeRefactor
Develop for SRP
•Code quality metrics•Coverage•SONAR
34
Develop for SRP
•Use other principles•High cohesion•Decrease coupling• Interfaces•Real encapsulation
•Law of Demeter
35
Develop for SRP
36
Keep it simple, stupid!
Keep it simple and short!
Keep it simple, short and specific!
Develop for SRP
•Naming•Think about it•Role play your entities•Longer and more focused name
37
Develop for SRP
• Extract method
• Extract class
38
Develop for SRP
•Refactor mercilessly
•Use design patterns
•Keep modularization clear
39
Example
40
Precise name(method, class)
Short class,35 lines
High cohesion
Conclusion
•OOD
•Clean code
•Better practice
41
Do 1 thingA class should have one reason to change!
SRP
Resources• http://butunclebob.com/ArticleS.UncleBob.Principles
OfOod• Uncle Bob about SRP
• http://www.codinghorror.com/blog/2007/03/curlys-law-do-one-thing.html• Coding Horror
• https://docs.google.com/file/d/0ByOwmqah_nuGNHEtcU5OekdDMkk/• PDF about SRP
• http://eyalgo.com/2014/02/01/the-single-responsibility-principle/• My blog post about SRP
42
Simple, Isn’t It?
43
Q & A
44
