REFACTORING – A WAY TO WRITE A

BETTER CODE

Andrew Chaa

Part 1

Questions, Slides, and Samples

Please feel free to ask questions anytime

Outline

Code that smells If it stinks, change it (Kent Beck’s

Grandma) Way to improve codes

What can you expect? “Clean code that works”

- Ron Jeffries Higher quality software Methodical approach to software

development

History of Refactoring

Kent Beck and War Cunningham in smalltalk

Martin Folwer’s famous book of Refactoring.

Supported by various tools now such as VS 2005/8, ReSharper, Eclipse …

Bad Smells in Code Duplicated Code Long Method Large Class Long Parameter List Divergent Change Switch Statement Temporary Field And many more…

Composing Methods

Extract Method Inline Method Inline Temp Replace Temp with Query Introduce Explaining Variable Split Temporary Variable Remove Assignments to Parameters Replace Method with Method Object Substitute Algorithm

void printOwing() {

printBanner();

//print details

System.out.println ("name: " + _name);

System.out.println ("amount " + getOutstanding());

}

void printOwing() { printBanner(); printDetails(getOutstanding());}

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

Extracting Method

Inline Methodint getRating() {

return (moreThanFiveLateDeliveries()) ? 2 : 1;

}

boolean moreThanFiveLateDeliveries() {

return _numberOfLateDeliveries > 5;

}

int getRating() {

return (_numberOfLateDeliveries > 5) ? 2 : 1;

}

Remove Tempdouble basePrice = anOrder.basePrice();

return (basePrice > 1000)

return (anOrder.basePrice() > 1000)

Replace Temp with Querydouble 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;

}

Introduce Explaining Variableif ( (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

}

Split Temporary Variabledouble temp = 2 * (_height + _width);

System.out.println (temp);

temp = _height * _width;

System.out.println (temp);

final double perimeter = 2 * (_height + _width);

System.out.println (perimeter);

final double area = _height * _width;

System.out.println (area);

Remove Assignments to Parametersint discount (int inputVal, int quantity, int yearToDate) {

if (inputVal > 50) inputVal -= 2;

int discount (int inputVal, int quantity, int yearToDate) {

int result = inputVal;

if (inputVal > 50) result -= 2;

Replace Method with Method Objectclass Order...

double price() {

double primaryBasePrice;

double secondaryBasePrice;

double tertiaryBasePrice;

// long computation;

...

}

Demo Extract method, amountFor(Rental each) Rename variable: thisAmount -> result Moving Method: to Rental, GetCharge Change the reference: each.GetCharge(); Replace Temp with Query: thisAmount Extract Method: frequentRenterPoints Move Method: frequentRenterPoints Remove Temp with Query: GetTotalCharge(); Remove Temp with Query:

GetTotalFrequentRenterPoints ();

Substitute AlgorithmString foundPerson(String[] people){

for (int i = 0; i < people.length; i++) {

if (people[i].equals ("Don")) { return "Don“;}

if (people[i].equals ("John")) { return "John“;}

if (people[i].equals ("Kent")) {return "Kent“;}

}

return "";

}

String foundPerson(String[] people){

List candidates = Arrays.asList(new String[] {"Don", "John", "Kent"});

for (int i=0; i<people.length; i++)

if (candidates.contains(people[i]))

return people[i];

return "";

}

Resources Refactoring catalogs:

http://www.refactoring.com/catalog/index.html

Podcast about Refactoringhttp://www.se-radio.net/index.php?post_id=172668

http://www.se-radio.net/index.php?post_id=205444

Refactoring (book)http://www.amazon.co.uk/Refactoring-Improving-Design-Existing-Technology/dp/0201485672/ref=sr_1_1?ie=UTF8&s=books&qid=1246371771&sr=8-1