Writing Good Code

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Writing Good Code<lecturer> Leo Liang </lecturer>

<date> 2009-7 </date>

Top right corner for field-mark, customer or partner logotypes. See Best practice for example.

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We are …

Programmer

Designer

Elegant Code


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Principles

Your code should

– be simple and clean– be readable and maintainable– be testable– be secure– be extensible


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Rule #1

get the job done


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Readable

Beautiful code is like poem

– Good code style– Meaningful naming– Short method– Appropriate class size

Unreadable code is unmaintainable

How To Write Unmaintainable Code? http://freeworld.thc.org/root/phun/unmaintain.html

白色马驹浮出雾中转瞬不见回到雾里秋日午后无花果树叶轻轻落下停在自己的影子上

--- 阿巴斯


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Simple & Clean

Choose the simplest way that could possibly work

Don’t repeat yourself– Reuse

High cohesion, low coupling– Design with contracts– Orthogonal ( 正交 )


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Robust

Robustness means two things:

– getting the job done

– continuing to get the job done as much as possible even when things go bad


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Performance vs. Style

Code style is more important than code performance– Consider readability and maintainability

Performance is very important

How the design is affects performance much more than how to code

– Performance is depends on a lot of factors– Design correctly– Identify the performance bottleneck by test or tool

Clever Code


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Don’t live with BAD code

Refactoring


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Principles

Your code should– get the job done– be simple and clean– be readable and maintainable– be testable– be secure– be extensible


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Coding Guidelines


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Why need code convention

Improve the readability Create maintainable code Eliminate potential bugs

– Bug pattern– Best practices

ClearCase merge

No absolutely good or bad Need unify convention in a team


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Programming Style Guidelines

Every product line has its own guidelines defined– SIG / ISP / MSDP / MIEP / AOP

General guidelines– Java Guidelines from Geotechnical Software Services

(http://geosoft.no/development/javastyle.html)– Excepts: 8 / 20 / 34 / 61 / 63 / 64

Take 20 minutes to go throw them!


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Naming Convention

Camel case– Types: nouns– Methods: verbs

TrafficProfile trafficProfile = createTrafficProfile();

Constants: all uppercase using underscore to separate words

setStatus( SERVICE_NOT_ACTIVE );


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Comment

JavaDoc– Classes, public methods

Comment on – where the code isn’t easy to understand – where the code differs to conventions

Unfinished task– // TODO: description

Know issue– // FIXME: description

Delete the unused code instead of comment out


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No warning

Target: No warning– Everyone has the responsibility to fix the warnings– Should check at code review

Suppress warning (Be careful!)– Java:

Annotate with @SuppressWarning– CheckStyle:

Suppress audit events between a comment containing CHECKSTYLE:OFF and a comment containing CHECKSTYLE:ON

– FindBugs:Edit the findbugs_exclude.xml


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Sample

Find code style issues from the sample code

sample.java


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Eclipse Usage

Eclipse built-in code style formatter– Menu: Source – Format– Keyboard: Ctrl-Shift-F

Rename an identifier is very easy in Eclipse– Menu: Refactor - Rename – Keyboard: Alt-Shift-R


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Code Check-in Rule

Before check-in your code, you must ensure– Code compiled successful– Basic test passed

Check-in frequency– As soon as possible– No longer than 1 day

Do not leave the file locked when you are not editing it

Write meaningful comment at check-in

Ensure the code in ClearCase is always valid


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Quick Reference


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Quick Reference – Naming Example

AudioSystem audioSystem; // NOT: audio_system

openDvdPlayer(); // NOT: openDVDPlayer();

getServiceCapability(); // NOT: getSc();

MAX_ITERATIONS = 25; void setTopic(Topic topic) // NOT: void setTopic(Topic value)

// NOT: void setTopic(Topic aTopic) // NOT: void setTopic(Topic t)

Collection<Point> points; // NOT: point

line.getLength(); // NOT: line.getLineLength();


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Quick Reference – Naming Example

void setFound(boolean isFound); // NOT: setIsFound(boolean isFound)// NOT: setFound(boolean found)

boolean hasLicense, canEvaluate, shouldAbort;

get/set, add/remove, create/destroy, start/stop, insert/delete, increment/decrement, old/new, begin/end, first/last, up/down, min/max, next/previous, old/new, open/close, show/hide, suspend/resume

xxxFactory, xxxProxy, xxxFacade, xxxCommandxxxExecption, xxxImpl, DefaultXxx, AbstractXxx


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Quick Reference - Comment

Comment as reminder// TODO: ……// FIXME: ……

Suppress warning– Java / FindBugs / PMD

@SuppressWarning– checkstyle

// CHECKSTYLE:OFFSome codes …// CHECKSTYLE:ON


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Quick Reference - Eclipse

Format code style– Source - Format (Ctrl-Shift-F)

Organize imports– Source - Organize imports (Ctrl-Shift-O)

Rename identify– Refactor - Rename (Alt-Shift-R)

Code clean up– Source - Clean up…

Error correct suggestion– Edit - Quick Fix (Ctrl-1)

More functions in Source and Refactor menu …

Writing Good Code

Technology

void settopic

boolean isfound

code

source

comment

rename

checkstyle

simple

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