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OBJECT CALISTHENICS Your code sucks, let's fix it!

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OBJECT Related to Object Oriented Programming.

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CALISTHENICS Term derived from greek, exercise, under the context of gymnastics.

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OBJECT CALISTHENICS Jeff Bay, in The ThoughtWorks Anthology, lists 9 rules to writing better Object Oriented code.

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MOTIVATION Readable Code, Comprehensible, Testable, Maintainable.

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1. ONLY ONE LEVEL OF INDENTATION PER METHOD

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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 ( ) ; } }

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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

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2. DON'T USE THE ELSE KEYWORD

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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 ' ) ; } }

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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 ' ) ; }

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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 ) ; }

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BUT ALSO Polymorphism Null Object Pattern Strategy Pattern State Pattern

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3. WRAP ALL PRIMITIVES AND STRINGS

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Encapsulate all the primitives within objects. http://c2.com/cgi/wiki?PrimitiveObsession

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If the variable of primitive type has a behavior, it MUST be encapsulated.

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It is especially true for Domain Driven Design.

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4. FIRST CLASS COLLECTIONS

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Any class that contains a collection should contain no other member variables.

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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)

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5. ONE DOT PER LINE

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LAW OF DEMETER Only talk to your immediate friends, don't talk to strangers.

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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 ( ) ; } }

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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 ( ) ) ; } }

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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 ( ) ; } }

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6. DON'T ABBREVIATE

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WHY DO YOU WANT TO ABBREVIATE?

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WRITE THE SAME NAME OVER AND OVER AGAIN? Then, your method is reused multiple times. Looks like code duplication.

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METHOD NAME TOO LONG? Maybe your class has multiple responsabilities. Violation of the Single Responsibility Principle.

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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/

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7. KEEP ALL ENTITIES SMALL

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No class over 50 lines and no package over 10 files.

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8. NO CLASSES WITH MORE THAN TWO INSTANCE VARIABLES

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YES, I KNOW!

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WHY? Low cohesion, better encapsulation.

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HOW? https://github.com/TheLadders/object-calisthenics#rule-8-no-classes-with-more...

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9. NO GETTERS/SETTERS/PROPERTIES

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Tell, don't ask. http://pragprog.com/articles/tell-dont-ask http://c2.com/cgi/wiki?TellDontAsk

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Getters/Setters violate the Open/Closed Principle.

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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

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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

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THANK YOU, QUESTIONS? williamdurand.fr github.com/willdurand twitter.com/couac