Code Refactoring

Milan Vukojewww.vukoje.net

Soprex

• SkfOffice2• SkfOffice3• Big5• Quality oriented• We are hiring…

Agenda

• Why is (clean) code important?• Refactoring (definition and samples)• Tools• When to and when not to refactor?• Summary

Is code important?

• Is construction relatively mechanical process?• Only activity that’s guaranteed to be done• 50-65% of overall effort• 50-75% of overall errors

Coding Horror

• Stress• Fear• Cargo cult programming• “Just in case” coding• Unusual software bugs (Heisenbug ,

Mandelbug, Schroedinbug… )

Code Example

Technical Debt

– If you can get today's work done today, but you do it in such a way that you can't possibly get tomorrow's work done tomorrow, then you lose. – Kent Beck

• When software organization chooses a design or construction approach that's expedient in the short term but that increases complexity and is more costly in the long term.

• Unintentional and intentional debt

Refactoring• Refactoring - a change made to the internal structure of software to

make it easier to understand and cheaper to modify without changing its observable behavior.

• Set of rules and techniques for enhancing code while reducing chances for error

• Refactoring: Improving the Design of Existing Code --Martin Fowler

Composing Methods 1. Extract Method void printOwing(double amount) { printBanner();

//print details System.out.println ("name:" + _name); System.out.println ("amount" + amount); }

void printOwing(double amount) { printBanner(); printDetails(amount); }

void printDetails (double amount) { System.out.println ("name:" + _name); System.out.println ("amount" + amount); }

Composing Methods 2. Inline Method

int getRating() { return (moreThanFiveLateDeliveries()) ? 2 : 1; } boolean moreThanFiveLateDeliveries() { return _numberOfLateDeliveries > 5; }

int getRating() { return (_numberOfLateDeliveries > 5) ? 2 : 1; }

Managing temps1. Inline Temp

double basePrice = anOrder.basePrice(); return (basePrice > 1000)

return (anOrder.basePrice() > 1000)

Managing temps 2. Replace Temp with Query

double basePrice = _quantity * _itemPrice; if (basePrice > 1000) return basePrice * 0.95; else return basePrice * 0.98;

if (basePrice() > 1000) return basePrice() * 0.95; else return basePrice() * 0.98;... double basePrice() { return _quantity * _itemPrice; }

Managing temps 3. Introduce Explaining Variable

if ( (platform.toUpperCase().indexOf("MAC") > -1) && (browser.toUpperCase().indexOf("IE") > -1) && wasInitialized() && resize > 0 ) { // do something }

final boolean isMacOs = platform.toUpperCase().indexOf("MAC") > -1; final boolean isIEBrowser = browser.toUpperCase().indexOf("IE") > -1; final boolean wasResized = resize > 0;

if (isMacOs && isIEBrowser && wasInitialized() && wasResized) { // do something }

Simplifying conditionals1. Decompose Conditional

if (date.before (SUMMER_START) || date.after(SUMMER_END)) charge = quantity * _winterRate + _winterServiceCharge; else charge = quantity * _summerRate;

if (notSummer(date)) charge = winterCharge(quantity); else charge = summerCharge (quantity);

Simplifying conditionals 2. Consolidate Duplicate Fragments

if (isSpecialDeal()) { total = price * 0.95; send(); } else { total = price * 0.98; send(); }

if (isSpecialDeal()) total = price * 0.95; else total = price * 0.98; send();

Simplifying conditionals 3. Consolidate Conditional Expression

double disabilityAmount() { if (_seniority < 2) return 0; if (_monthsDisabled > 12) return 0; if (_isPartTime) return 0; // compute the disability amount

double disabilityAmount() { if (isNotEligableForDisability()) return 0; // compute the disability amount

Moving Features between objects

• Replace Method with Method Object• Extract/Inline Class• Pull Up/Down Field/Method• Extract Subclass/ Superclass/Interface• Collapse Hierarchy

Benefits• Less code – less bugs

• Readable business logic – better business domain understanding

• Self explaining code– Less documentation and faster changes

• Better design – Higher encapsulation and reusability– Cleaner concepts and structure

Visual Studio 2008

Need for refactoring • Why change something that works?

– We want programs that are easy to read, that have all logic specified in one and only one place, that do not allow changes to endanger existing behavior, and that allow conditional logic to be expressed as simply as possible. --Kent Beck

• Micro design - clear API and logical structures• Code evolution - Embracing change• Avoiding coding horror by managing complexity• Agile methods (XP, TDD, Scrum)

When Should You Refactor?• Not having enough time usually is a sign that you need to do some

refactoring. – Martin Fowler

• Refactor all the time in little steps• Refactor when you:– add function– fix a bug – do a code review

• Refactoring and Unit Tests?

Code smells

• Duplicated Code• Long Method • Large Class• Switch Statements • Lazy Class • Speculative Generality• Temporary Field• Message Chains• …

When you shouldn’t refactor?Avoid refactoring:• Databases• Published interfaces• Code is so full of bugs that you cannot stabilize it• When you are very close to a deadline• When you are not sure

• Don’t overdo it (no silver bullet)– Perfect is the enemy of good, and good is what we want

Performance and Refactoring

• Performance optimization = obscure code• Optimized for humans = slower code but

easier tuning• 10% optimized code is usually enough

What Do I Tell My Manager?

• If the manager is quality oriented, then the thing to stress is the quality aspects.

• Tons of studies show that technical reviews are an important way to reduce bugs and thus speed up development.

• Don't tell!?

Summary

1. Programming is hard and complex2. (Clean) Code is very important3. Refactoring can help you achieve clean code

and better design.4. Refactoring should be used wisely

1. Don’t over do it (no silver bullet)2. Know when not to refactor3. Changes must not cause new bugs

Questions?

Milan Vukojewww.vukoje.net

vukoje@gmail.com

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