clean code
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Clean Code
Presentation of the Uncle Bob's Book.
1Thursday, December 1, 11
The Speaker
• Brice Argenson– Full Professor in Java and Web Technologies
• Professional Experiences :
• Certifications :
– Bug Out PC– ADF– Adullact– Webpulser
– Audaxis– Groupe Open– Atos Worldline– Xebia IT
– SCJP 6– SCWCD 5
– MCP – Exam 70-316
brice.argenson@supinfo.com @bargenson
2Thursday, December 1, 11
Agenda
• Software Craftsmanship
• Why Clean Code ?
• Tips & Tricks to write Clean Code
• References
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SOFTWARE CRAFTSMANSHIPWhat is that ?
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WHY CLEAN CODE ?Bad Code VS. Clean Code
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Bad Code
• Bad Code killed some companies– Rushed the product to market– More and more features– Worse and worse code– Code unmanageable
• We all wrote bad code– Trying to go fast ?– We were in a rush ?– We’ll clean it up later…
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The Cost of Bad Code
• Do you have been slowed down by messy code ?
• More & more mess è Less & less productivity
• When productivity became terrible è Redesign
• And again…• And again…
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Whose Fault ?
• The customer ?– The requirements change too much ?
• The managers ?– The deadlines are too short ?
• It is mainly the developer fault !– The others look to us for the information they need– The doctor knows more than the patient about the risks
[…]
• Be professionals !
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What is Clean Code ?
• What is Clean Code for you ?– It is working ?– It is efficient ?– It is short ?
• Clean Code is easy to read !
• We are authors !
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What is Clean Code ?
• The Boy Scout Rule :– Leave the campground cleaner than you found it.
• Refactor your code !
• Write tests !– Test Driven Development
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GET YOUR HANDS DIRTY !How to write Clean Code ?
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Meaningful Names
• What is the purpose of this code ?
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Meaningful Names
• And what do you think of this code ?
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Meaningful Names
• Use Intention-Revealing Names
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Meaningful Names
• What about Hungarian Notation ?
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Meaningful Names
• What if one day we change the type ?
• Hungarian Notation make it harder to change the name or type of a variable, function or class
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Meaningful Names
• What about Member Prefixes ?– Example: m_firstName
• Classes and functions should be small enough that you don’t need them
• IDE highlights or colorizes members !
• Prefixes become unseen clutter
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Functions
• What do you think about this method ?– FitNesse - commit 3bec390e6f
• And now ?– FitNesse - commit 7491001db7
• What has changed ?
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Functions
• Small !– Not bigger than a screen full
• Correct in the eighties (24 x 80)
– Should be transparently obvious– Indent level should not be greater than one or two
• Do one thing !– Your function is divided into section ?
• You can divide it !
• The Stepdown Rule !– We want the code to read like a top-down narrative
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Functions
• Function arguments ?– Niladic
• The ideal number
– Monadic• A good number
– Dyadic• A good number
– Triadic• Should be avoided
– Polyadic• Do you need to wrap the arguments into a new type ?
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Error Handling
• What do you think about this code ?
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Error Handling
• Prefer exceptions to returning error codes
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Error Handling
• And what do you think about this code ?
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Error Handling
• For you what is the most common exception ?– NPE !
• How to avoid it ?
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Error Handling
• What do you think about this code ?
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Error Handling
• Don’t return Null !
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Error Handling
• What do you think about this code ?
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Error Handling
• How to make code look like that ?
• Special Case object !
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Side Effects
• Consider the following class :
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Side Effects
• Consider the following code :
• Do you see the problem ?
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Side Effects
• To protect the internals of a Period instance from this sort of attack:
– You must make defensive copy of each mutable parameter to the constructor !
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Side Effects
• Inheritance is a powerful way to achieve code reuse– But not always the best !
• Inheritance from ordinary concrete classes across package boundaries is dangerous !
• Unlike method invocation, inheritance violates encapsulation
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Side Effects
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Side Effects
• What this code display ?
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Side Effects
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Side Effects
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Side Effects
• Design of the InstrumentedSet is extremely flexible :– Implement the Set interface– Receive an argument also of type Set
• With inheritance, we could work only with HashSet
• With composition, we can work with any Set implementation !
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Side Effects
• Favor composition over inheritance !
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REFERENCESDo you want to read more about the subject ?
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Books
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Clean CodeA Handbook of Agile Software Craftsmanship
Robert C. Martin (aka. Uncle Bob)
Prentice Hall editions
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Books
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Effective JavaSecond Edition
Joshua Bloch
Addison Wesley editions
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Links
• Sign the Manifesto – http://manifesto.softwarecraftsmanship.org
• Software Craftsmanship en pratique - Xebia– http://blog.xebia.fr/2011/01/31/software-craftsmanship-
en-pratique/
• The Clean Coder - Uncle Bob blog– http://thecleancoder.blogspot.com/
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