Object Calisthenics (APIHour #2)

Object Calisthenics are basically exercises to writing better oriented object code. It is a set of 9 rules introduced by Jeff Bay in "The ThoughtWorks Anthology".

Online slides: http://williamdurand.fr/object-calisthenics-slides/
Source: https://github.com/willdurand/object-calisthenics-slides

Transcript

1. OBJECT CALISTHENICS Your code sucks, let's fix it!
2. OBJECT Related to Object Oriented Programming.
3. CALISTHENICS Term derived from greek, exercise, under the context of gymnastics.
4. OBJECT CALISTHENICS Jeff Bay, in The ThoughtWorks Anthology, lists 9 rules to writing better Object Oriented code.
5. MOTIVATION Readable Code, Comprehensible, Testable, Maintainable.
6. 1. ONLY ONE LEVEL OF INDENTATION PER METHOD
7. YAY! c l a s s B o a r d { p u b l i c S t r i n g b o a r d ( ) { S t r i n g B u i l d e r b u f = n e w S t r i n g B u i l d e r ( ) ; / / 0 f o r ( i n t i = 0 ; i < 1 0 ; i + + ) { / / 1 f o r ( i n t j = 0 ; j < 1 0 ; j + + ) { / / 2 b u f . a p p e n d ( d a t a [ i ] [ j ] ) ; } b u f . a p p e n d ( " \ n " ) ; } r e t u r n b u f . t o S t r i n g ( ) ; } }
8. EXTRACT METHOD p u b l i c S t r i n g b o a r d ( ) { S t r i n g B u i l d e r b u f = n e w S t r i n g B u i l d e r ( ) ; c o l l e c t R o w s ( b u f ) ; r e t u r n b u f . t o S t r i n g ( ) ; } p r i v a t e v o i d c o l l e c t R o w s ( S t r i n g B u i l d e r b u f ) { f o r ( i n t i = 0 ; i < 1 0 ; i + + ) { c o l l e c t R o w ( b u f , i ) ; } } p r i v a t e v o i d c o l l e c t R o w ( S t r i n g B u i l d e r b u f , i n t r o w ) { f o r ( i n t i = 0 ; i < 1 0 ; i + + ) { b u f . a p p e n d ( d a t a [ r o w ] [ i ] ) ; } b u f . a p p e n d ( " \ n " ) ; } http://refactoring.com/catalog/extractMethod.html
9. 2. DON'T USE THE ELSE KEYWORD
10. EXAMPLE p u b l i c v o i d l o g i n ( S t r i n g u s e r n a m e , S t r i n g p a s s w o r d ) { i f ( u s e r R e p o s i t o r y . i s V a l i d ( u s e r n a m e , p a s s w o r d ) ) { r e d i r e c t ( ' h o m e p a g e ' ) ; } e l s e { a d d F l a s h ( ' e r r o r ' , ' B a d c r e d e n t i a l s ' ) ; r e d i r e c t ( ' l o g i n ' ) ; } }
11. EARLY RETURN p u b l i c v o i d l o g i n ( S t r i n g u s e r n a m e , S t r i n g p a s s w o r d ) { i f ( ! u s e r R e p o s i t o r y . i s V a l i d ( u s e r n a m e , p a s s w o r d ) ) { a d d F l a s h ( ' e r r o r ' , ' B a d c r e d e n t i a l s ' ) ; r e t u r n r e d i r e c t ( ' l o g i n ' ) ; } r e d i r e c t ( ' h o m e p a g e ' ) ; }
12. VARIABLE p u b l i c v o i d l o g i n ( S t r i n g u s e r n a m e , S t r i n g p a s s w o r d ) { S t r i n g r e d i r e c t R o u t e = ' h o m e p a g e ' ; i f ( ! u s e r R e p o s i t o r y . i s V a l i d ( u s e r n a m e , p a s s w o r d ) ) { a d d F l a s h ( ' e r r o r ' , ' B a d c r e d e n t i a l s ' ) ; r e d i r e c t R o u t e = ' l o g i n ' ; } r e d i r e c t ( r e d i r e c t R o u t e ) ; }
13. BUT ALSO Polymorphism Null Object Pattern Strategy Pattern State Pattern
14. 3. WRAP ALL PRIMITIVES AND STRINGS
15. Encapsulate all the primitives within objects. http://c2.com/cgi/wiki?PrimitiveObsession
16. If the variable of primitive type has a behavior, it MUST be encapsulated.
17. It is especially true for Domain Driven Design.
18. 4. FIRST CLASS COLLECTIONS
19. Any class that contains a collection should contain no other member variables.
20. Each collection gets wrapped in its own class, so now behaviors related to the collection have a home. (e.g. filter methods, applying a rule to each element)
21. 5. ONE DOT PER LINE
22. LAW OF DEMETER Only talk to your immediate friends, don't talk to strangers.
23. EXAMPLE c l a s s L o c a t i o n { c l a s s P i e c e { p u b l i c P i e c e c u r r e n t ; p u b l i c S t r i n g r e p r e s e n t a t i o n ; } } c l a s s B o a r d { p u b l i c S t r i n g b o a r d R e p r e s e n t a t i o n ( ) { S t r i n g B u i l d e r b u f = n e w S t r i n g B u i l d e r ( ) ; f o r ( L o c a t i o n l o c : s q u a r e s ( ) ) { b u f . a p p e n d ( l o c . c u r r e n t . r e p r e s e n t a t i o n . s u b s t r i n g ( 0 , 1 ) ) ; } r e t u r n b u f . t o S t r i n g ( ) ; } }
24. TALK TO YOUR FRIENDS! c l a s s L o c a t i o n { p r i v a t e P i e c e c u r r e n t ; p u b l i c v o i d a d d T o ( S t r i n g B u i l d e r b u f ) { c u r r e n t . a d d T o ( b u f ) ; } } c l a s s P i e c e { p r i v a t e S t r i n g r e p r e s e n t a t i o n ; p u b l i c S t r i n g c h a r a c t e r ( ) { r e t u r n r e p r e s e n t a t i o n . s u b s t r i n g ( 0 , 1 ) ; } p u b l i c v o i d a d d T o ( S t r i n g B u i l d e r b u f ) { b u f . a p p e n d ( c h a r a c t e r ( ) ) ; } }
25. TALK TO YOUR FRIENDS! / / B e f o r e : / / b u f . a p p e n d ( l o c . c u r r e n t . r e p r e s e n t a t i o n . s u b s t r i n g ( 0 , 1 ) ) ; / / A f t e r : c l a s s B o a r d { p u b l i c S t r i n g b o a r d R e p r e s e n t a t i o n ( ) { S t r i n g B u i l d e r b u f = n e w S t r i n g B u i l d e r ( ) ; f o r ( L o c a t i o n l o c a t i o n : s q u a r e s ( ) ) { l o c a t i o n . a d d T o ( b u f ) ; } r e t u r n b u f . t o S t r i n g ( ) ; } }
26. 6. DON'T ABBREVIATE
27. WHY DO YOU WANT TO ABBREVIATE?
28. WRITE THE SAME NAME OVER AND OVER AGAIN? Then, your method is reused multiple times. Looks like code duplication.
29. METHOD NAME TOO LONG? Maybe your class has multiple responsabilities. Violation of the Single Responsibility Principle.
30. Me — 2 hours ago If you can't find a decent name for a class or a method, something is probably wrong with your conception. Rethink! http://williamdurand.fr/2012/01/24/designing-a-software-by-naming-things/
31. 7. KEEP ALL ENTITIES SMALL
32. No class over 50 lines and no package over 10 files.
33. 8. NO CLASSES WITH MORE THAN TWO INSTANCE VARIABLES
34. YES, I KNOW!
35. WHY? Low cohesion, better encapsulation.
36. HOW? https://github.com/TheLadders/object-calisthenics#rule-8-no-classes-with-more...
37. 9. NO GETTERS/SETTERS/PROPERTIES
38. Tell, don't ask. http://pragprog.com/articles/tell-dont-ask http://c2.com/cgi/wiki?TellDontAsk
39. Getters/Setters violate the Open/Closed Principle.
40. GETTERS/SETTERS ARE EVIL / / G a m e p r i v a t e i n t s c o r e ; p u b l i c v o i d s e t S c o r e ( i n t s c o r e ) { t h i s . s c o r e = s c o r e ; } p u b l i c i n t g e t S c o r e ( ) { r e t u r n s c o r e ; } / / U s a g e g a m e . s e t S c o r e ( g a m e . g e t S c o r e ( ) + E N E M Y _ D E S T R O Y E D _ S C O R E ) ; / / G a m e p u b l i c v o i d a d d S c o r e ( i n t d e l t a ) { s c o r e + = d e l t a ; } / / U s a g e g a m e . a d d S c o r e ( E N E M Y _ D E S T R O Y E D _ S C O R E ) ; http://stackoverflow.com/questions/565095/are-getters-and-setters-evil http://whitewashing.de/2012/08/22/building_an_object_model__no_setters_allowed.html
41. RECAP' 1. Only One Level Of Indentation Per Method 2. Don't Use The ELSE Keyword 3. Wrap All Primitives And Strings 4. First Class Collections 5. One Dot Per Line 6. Don't Abbreviate 7. Keep All Entities Small 8. No Classes With More Than Two Instance Variables 9. No Getters/Setters/Properties
42. THANK YOU, QUESTIONS? williamdurand.fr github.com/willdurand twitter.com/couac