Clean Code

Hendrik Ebel10. Mar. 2009

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TopicsMotivationMeaningful NamesCommentsFunctionsObjects and Data StructuresError HandlingUnit Tests

By Robert C. Martin & Co.Object Mentor Inc.

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What is Clean Code?One Question ...

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What is Clean Code?One Question ...

elegantefficient

easy to enhance

simple and direct

readabilitylike a well-written prose

careno duplications

was made for the problem...many answers!

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What is Clean Code?One Question ...

elegantefficient

easy to enhance

simple and direct

readabilitylike a well-written prose

careno duplications

was made for the problem...many answers!

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Motivation

The Total Cost of Owning a Mess

productivity vs. time

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Aims of Clean Code

producing better code@author writing for readerscode has to be kept clean over time„Leave the campground cleaner than you found it.“

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Meaningful Names

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Meaningful Namesvariable, function or class names should answer all the big questions:

why it exists?what it does?how it is used?

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Meaningful NamesIf a name requires a comment, then the name does not reveal its intentavoid disinformation

don't use type information in names (example: personList)Spelling similar concepts similarly is information. Using inconsistent spellings is disinformation.

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Comments

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Good and Bad Comments•Public API Comments•Legal Comments•Explanation of Intent•Warning for

Consequences•real TODO Comments

•Redundant Comments•Noise Comments•Position Markers•Closing Brace Comments•Commented-Out Code•Obsolete Comments•Nonpublic JavaDocs

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Comments

„Purpose of a comment is to explain code that does not explain itself.“Comments do not make up for bad codeDon‘t use a comment when you can use a function or a variableComments can contains lies

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Functions

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FunctionsThe goal is to tell the story of the system.„The first rule of functions is that they should be small.“Do One Thing!Stepdown Rule

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FunctionsIdeal number of arguments is zero More than three should‘t be used anywayFlag arguments are ugly.Avoid output argumentsSide effects are lies.

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Objects and Data Structures

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Objectshide data and expose functionseasy to add new objectshard to add new behaviors

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Data Structuresexpose data and have no meaningful functionseasy to add new behaviors hard to add new data structures

Choose the approach that is best for the job.

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Error Handling

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Error Handling

Write code that is clean and rebustSee error handling as a separate concernUse exceptions rather than return codesUse unchecked exceptions

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Error HandlingDon‘t return NULL

throwing an exception or a special case object like „Collections.emptyList()“

Don‘t pass NULLInvalidArgumentExceptions or assert better: forbid passing NULL by default

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Unit Tests

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Unit TestsTest Driven Development (TDD)

test and production code are written togethertests just a few seconds ahead

Keeping tests cleanTest code is just as important as production code.

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Unit TestsOne Assert or Single Concept per TestF.I.R .S.T.

FastIndependentRepeatable (in any environment)Self-ValidationTimly

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Thanks - Any Questions?

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Sources Book

„Clean Code“ by Robert C. Martin ISBN: 0132350882

Imageshttp://www.failblog.org http://www.flickr.com/photos/hugovk/199425487/http://www.flickr.com/photos/jackpot321/1809424991/http://www.osnews.com/story/19266/WTFs_m

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