Refactoring

Refactoring is a disciplined
technique for restructuring
an existing body of code,
altering its internal
structure without changing
its external behavior.
Martin Fowler
Refactoring, improving design of existing code

Any fool can write code that
a computer can understand.
Good programmers write code
that humans can understand
Martin Fowler

Remove duplication
Remove duplication
Remove duplication

Make code readable
(by humans)

100% sure the new
code is better

Cost Not to Refactor
greater than
Cost to Refactor

Cost = Doing the change
+ Testing it
+ Documentation

Only refactor if you
are conﬁdent

(it works as before, no side effects)

Communication
between
components

Given input
When doing YYY
Expect output

C#

public double SomeMethod()
{
var result = 0d;
if (_firstGuard)
{
result = FirstCalculation();
if (_secondGuard)
{
result = SecondCalculation();
}
}
return result;
}

C#

RE

public double BetterMethod()
{
if (!_firstGuard)
{
return 0;
}
if (!_secondGuard)
{
return FirstCalculation();
}
return SecondCalculation();
}

FAC
TO
R

ED

Ruby

class NestedCalculation
def awesome_method
first_calculation
||
second_calculation ||
default_calculation
end
def first_calculation
@first_guard && some_calc_here
end
def second_calculation
# etc...
end
end

RE

FAC
TO
R

ED

C#

public double SomeMethod()
{
var result = 0d;
if (_guard1)
{
if (_guard2)
{
if (_guard3)
{
result = Calc1() + Calc2();
}
}
}
return result;
}

C#

public double BetterMethod()
{
if (_guard1 && _guard2 && _guard3)
{
return Calc1() + Calc2();
}
return 0;
}

RE

FAC
TO
R

ED

C#

public bool SomeMethod()
{
var result = false;
if (_firstGuard)
{
if (_secondGuard)
result = true;
}
else
result = true;
return result;
}

C#

RE

public bool BetterMethod()
{
return !_firstGuard || _secondGuard;
}

FAC
TO
R

ED

Java

public Iterable<String> deploy(
Iterable<String> collection) {
Collection<String> result = new ArrayList<>...;
Iterator<String> cursor = collection.iterator();
while(cursor.hasNext()) {
result.add("Deployed to " + cursor.next());
}
return result;
}

Java

public Iterable<String> betterDeploy(
Iterable<String> environments) {

RE

FAC
TO
R

return with(environments)
.convert(new DeployConverter());
}
class DeployConverter
implements Converter<String, String> {
public String convert(String env) {
return "Deployed to " + env;
}
}

ED

Scala

RE

FAC
TO
R

def betterDeploy(environments: Iterable[String])
: Iterable[String] {
environment.map env => s"Deploy to $env"
}

ED

Java

public class Movie {
private String title;
private int review;
public Movie(String title, int review) {
this.title = title;
this.review = review;
}
public String getTitle() {...}
public int getReview() {...}
}

Java

@Test
public void whereAreMyPostIt() {

RE

FAC
TO
R

ED

// arrange
Iterable<Movie> movies = asList(
new Movie("Blazing Saddles", 5), new Movie("Terminator"),
new Movie("Canadian Bacon", 8)
);
// act
Iterable<Movie> reviewed =
filter(having(on(Movie.class).getReview(), greaterThan(-1))
, movies);
// assert
assertThat(joinFrom(reviewed).getTitle(),
equalTo("Blazing Saddles, Canadian Bacon"));
}

Java

@Test
public void wheresMyGanttChart() {

RE

FAC
TO
R

ED

// arrange
Iterable<Movie> movies = asList(new Movie("Blazing Saddles"),
new Movie("Terminator"), new Movie("Curator"));
// act
Matcher<Movie> endsWithAtor = new Predicate<Movie>() {
public boolean apply(Movie item) {
return item.getTitle().endsWith("ator");
}
};
Iterable<Movie> actual = filter(endsWithAtor, movies);
// assert
assertThat(joinFrom(actual).getTitle(),
equalTo("Terminator, Curator"));
}

C#

public int Mysterious(IEnumerable<int> collection)
{
return collection.Aggregate((a, b) => a + b);
}

Coffee

[1..1000].reduce (t, s) -> t + s

Coffee

class BudgetViewModel
constructor: (json) ->
@budgets
= [2013, 2012, 2011]
@budgetIndex = 0
salary: ->
return 5000 if @budgetIndex == 0
return 2000 if @budgetIndex == 1
1000

Coffee

RE

constructor: ->
@budgets = [
new BudgetModel(2013, 5000),
new BudgetModel(2011, 1000)
]
@budget = @budgets[0]
salary: => @budget.salary

FAC
TO
R

ED

Coffee
KO


RE

FAC
TO
R

constructor: ->
@budgets = ko.observableArray [
new BudgetModel(2011, 1000)
]
@budget = ko.observable()
@salary = ko.computed => @budget().salary

ED

Language is your friend
(or it should be)

Coffee

class window.NewsViewModel
constructor: (@limit = -1) ->
@news = ko.observableArray()
@title = ko.observable()
$.getJSON '../api/news', @loadNews
loadNews: (data) =>
max = (if @limit == -1 then -1 else @limit - 1)
@news(@createNewsItem(e) for e in data[0..max])
@title @news()[0]?.Title
createNewsItem: (e) =>
newsItem =
Title: e.Title
Date: @parseDate(e.Date)
Body: e.Body

JS
(function() {
var __bind = function(fn, me){ return function(){ return fn.apply(me, arguments); }; };
window.NewsViewModel = (function() {
function NewsViewModel(limit) {
this.limit = limit != null ? limit : -1;
this.createNewsItem = __bind(this.createNewsItem, this);
this.loadNews = __bind(this.loadNews, this);
this.news = ko.observableArray();
this.title = ko.observable();
$.getJSON('../api/news', this.loadNews);
}
NewsViewModel.prototype.loadNews = function(data) {
var e, max, _ref;
max = (this.limit === -1 ? -1 : this.limit - 1);
this.news((function() {
var _i, _len, _ref, _results;
_ref = data.slice(0, max + 1 || 9e9);
_results = [];
for (_i = 0, _len = _ref.length; _i < _len; _i++) {
e = _ref[_i];
_results.push(this.createNewsItem(e));
}
return _results;
}).call(this));
return this.title((_ref = this.news()[0]) != null ? _ref.Title : void 0);
};
NewsViewModel.prototype.createNewsItem = function(e) {
var newsItem;
return newsItem = {
Title: e.Title,
Date: this.parseDate(e.Date),
Body: e.Body
};
};
return NewsViewModel;
})();
}).call(this);

JVM supports
multiple languages

Tests are a great
place to start

amir@barylko.com
@abarylko
http://bit.ly/abarylkop

Photo Credit
•

Under http://creativecommons.org/licenses/by/2.5/

•
•

Bill Ward, Derek Schin's Trucks 1, http://flic.kr/p/m5L5S

•

Jeremy Keith, Roast beef, http://flic.kr/p/TKUz

•

Rob Campbell, Field of daisies, http://flic.kr/p/6QJjU4

•

•

Joe Cheng, DSC_7820-01, http://flic.kr/p/2Zt2u

Karin Dalziel, The Thinker, http://flic.kr/p/4UYArc

Under http://creativecommons.org/licenses/by-sa/3.0/us/

•

Derick Bailey, SOLID Motivational Posters, http://bit.ly/17aVaHg

Photo Credit 2
•
•

How to write good code, http://xkcd.com/844/
Understanding flow charts, http://lifehacker.com/5909501/how-tochoose-the-best-chart-for-your-data

Resources
•
•

http://www.infoq.com/news/2010/06/decision-to-refactor

•
•
•

Refactoring Catalog: http://www.refactoring.com/catalog/

http://stackoverflow.com/questions/38635/what-static-analysis-toolsare-available-for-c

LambdaJ: https://code.google.com/p/lambda
Coffeescript: http://coffeescript.org/

Refactoring

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