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Refactoring Legacy SystemsRefactoring Legacy Systems

Willem van den Ende willem@livingsoftware.nlMarc Evers - marc@piecemealgrowth.nl

2007 Living Software & Piecemeal Growth Some Rights Reserved

Piecemeal GrowthPiecemeal Growth

Living Software B.V.Living Software B.V.

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A designer knows he has achieved perfection

not when there is nothing left to add,but when there is nothing left to take away.

Antoine de Saint-Exupry

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About UsDesign Debt Cycle

Refactoring Legacy CodeApproaches

DemoQ&A

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4

Who we areWho we are

Willem van den Ende

Refactoring

1996 New Legacy Application

Teams

Independent (Living Software B.V.)

All-hands person

Software development coach Trainer

Consultant

blog: me.andering.com

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5

Who we areWho we are

Marc EversMarc Evers

Independent (Piecemeal Growth)Independent (Piecemeal Growth)

Software development coachSoftware development coach

TrainerTrainer

ConsultantConsultant

Blog: blog.piecemealgrowth.netBlog: blog.piecemealgrowth.net

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6

What we doWhat we do

More business value from software developmentMore business value from software development

andand

helping others do ithelping others do it

throughthrough

Coaching & mentoringCoaching & mentoring

TrainingTraining

FacilitationFacilitation

Organizing conferencesOrganizing conferences

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Legacy CodeLegacy Code

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Legacy CodeLegacy Code

Legacy code = code without tests

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Design Debt CycleDesign Debt Cycle

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There is light at the end of the tunnel!There is light at the end of the tunnel!

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Refactoring Legacy CodeRefactoring Legacy Code

Improving the internal structure of softwareImproving the internal structure of softwarewithout changing its external behaviourwithout changing its external behaviour

Tiny, safe, almost mechanical stepsTiny, safe, almost mechanical steps

Unit tests!Unit tests!

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Refactoring approachesRefactoring approaches

Cut at the seamsCut at the seams

Reveal intentionsReveal intentions

Use your toolsUse your tools One smell at a timeOne smell at a time

Pairs & peersPairs & peers

Exploratory refactoringExploratory refactoring Sometimes it gets worse before it gets betterSometimes it gets worse before it gets better

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Cut at the seamsCut at the seams

Seam = place where you can alter behaviourSeam = place where you can alter behaviour

in a program without editing in that placein a program without editing in that place

Seam typesSeam types

Preprocessing seamPreprocessing seam

Link seamLink seam

Object seamObject seam

Break dependenciesBreak dependencies

To add testsTo add tests

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Object seam exampleObject seam examplepublic class Spreadsheet {public class Spreadsheet {

public Spreadsheet buildSheet(Cell cell) {public Spreadsheet buildSheet(Cell cell) {

......

recalculate(cell);recalculate(cell);

......

}}

public void recalculate(Cell cell) { ... }public void recalculate(Cell cell) { ... }

......

}}

public class TestingSpreadsheet extends Spreadsheet {public class TestingSpreadsheet extends Spreadsheet {

public void recalculate(Cell cell) {public void recalculate(Cell cell) {

......

}}

}}

(based on(based on Working Effectively with Legacy CodeWorking Effectively with Legacy Code, p. 42/43), p. 42/43)

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Reveal intentionsReveal intentions

Write code for who comes after you,not for the computer

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Use your toolsUse your tools

Canned refactoringsCanned refactorings

Extract method, extract local variableExtract method, extract local variable

Rename method, rename class, rename variableRename method, rename class, rename variable

Extract interfaceExtract interface

Code analysisCode analysis

Eclipse compiler warnings/errorsEclipse compiler warnings/errors

PMDPMD

Basic code hygieneBasic code hygiene

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One smell at a timeOne smell at a time

Code smellCode smell

warning sign aboutwarning sign aboutpossible problempossible problem

God classGod classLong methodLong method

Duplicated codeDuplicated code

Intention hiding namesIntention hiding names

Focus!Focus!

Refactoring backlogRefactoring backlog

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Pairs & peersPairs & peers

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SometimesSometimes

it gets worseit gets worse

DefactoringDefactoring

Temporarily use not-so-good practicesTemporarily use not-so-good practices

before itbefore it

gets bettergets better

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Refactor as you goRefactor as you go

Exploratory RefactoringExploratory Refactoring

Clean what you're working onClean what you're working on

Always leave it in a better state than when youAlways leave it in a better state than when you

startedstarted

Add TestsAdd Tests

Persevere!Persevere!

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DemoDemo

CoffeeMUDCoffeeMUD

www.zimmers.net/home/mud/www.zimmers.net/home/mud/

sourceforge.net/projects/coffeemudsourceforge.net/projects/coffeemud

Multi User DungeonMulti User Dungeon JavaJava

3066 classes3066 classes

33210 methods33210 methods

340 Kloc340 Kloc

Open sourceOpen source

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CoffeeMUDCoffeeMUD

MOB = any creature in the worldMOB = any creature in the world

StdMOBStdMOB

Smells: god class, large class, long methodsSmells: god class, large class, long methods

Collaborators: Ability, Behavior, Item, Faction, DeityCollaborators: Ability, Behavior, Item, Faction, Deity

Interfaces: MsgListener, EnvironmentalInterfaces: MsgListener, Environmental

bli b l kM (E i t l H t CMM ) {

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public boolean okMessage(Environmental myHost, CMMsg msg) {

try {

checkNotDeity(msg);

checkCharacterStats(msg);

checkEffects(msg);

checkInventories(msg);

checkBehaviours(msg);

checkFactions(msg);

MOB mob = msg.source();

checkImmortalityAndLimbs(msg, mob);checkConsequencesOfRange(msg, mob);

if (targetHasEffect(msg) && (msg.amITarget(this))) {

checkIAmPresentInWorld();

performCombat(msg, mob);

if ((rangeToTarget() >= 0) && (!isInCombat()))setAtRange(-1);

checkCanDoActionToTarget(msg, mob);

}

invokeDepressionAroundMyDeath(msg);

...

}

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ReferencesReferences

Martin Fowler,Martin Fowler, RefactoringRefactoring

William C. Wake,William C. Wake, Refactoring WorkbookRefactoring Workbook

Micheal Feathers,Micheal Feathers, Working Effectively withWorking Effectively withLegacy CodeLegacy Code

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CopyrightCopyright

This work is licensed under a Creative Commons Attribution-Share Alike 3.0This work is licensed under a Creative Commons Attribution-Share Alike 3.0Netherlands license - http://creativecommons.org/licenses/by-sa/3.0/nl/Netherlands license - http://creativecommons.org/licenses/by-sa/3.0/nl/

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