You have found the more you change the code, the more difficult it becomes. Refactoring is a developer practice of improving the internal structure of existing code without changing the external behaviour. It makes code changes for present or future easier. You may have heard about Refactoring from colleagues, books, articles and have probably tried or hear it the first time. This talk presents what it is, why it is important and what you can do to get better at it based on the experience of mentoring on technical practices to others. This talk is suitable for people who are experienced in programming, have met the challenges of making changes and want to deepen their skill. Demo included!

1. GET BETTER AT REFACTORING
stanly@odd-e.com
@stanlylau

2. INTRODUCTION
ABOUT ME
▸ Lives in Singapore
▸ Software development coach /
mentor
▸ Goal: Reduce the cost of change
▸ Agile Singapore community

3. 1. PROBLEM
2. REFACTORING
3. DEMO
4. TIPS

4. @RequestMapping(value = "/send", method = RequestMethod.POST)
public String post(@ModelAttribute MailSendForm form, Model model) {
model.addAttribute("form", form);
return "send";
}
loc: 4

5. @RequestMapping(value = "/send", method = RequestMethod.POST)
public String post(@ModelAttribute MailSendForm form, Model model) {
// TODO Validate Request
String address = form.getAddress();
boolean isMailAddress = Validator.isMailAddress(address);
if (!isMailAddress) {
model.addAttribute("form", form);
model.addAttribute("error", "error");
return "send";
}
String subject = form.getSubject();
boolean isSubject = Validator.isSubject(subject);
String body = form.getBody();
boolean isBody = Validator.isBody(body);
// TODO Mail Send
// TODO Show the page
model.addAttribute("form", form);
return "send";
}
loc: 14

6. @RequestMapping(value = "/sendEmail", method = RequestMethod.POST)
public String sendEmail(@ModelAttribute MailSendForm form, Model model) {
if (!Validator.isMailAddress(form.getAddress())) {
model.addAttribute("error", "error");
return "send";
}
if (!Validator.isSubject(form.getSubject())) {
model.addAttribute("error", "error");
return "send";
}
if (!Validator.isBody(form.getBody())) {
model.addAttribute("error", "error");
return "send";
}
MailInfo mail = new MailInfo("gadget.mailsender@gmail.com",
form.getAddress(), form.getSubject(), form.getBody());
try {
mailService.send(mail);
} catch (Exception e) {
e.printStackTrace();
}
return "send";
}
loc: 17

7. @RequestMapping(value = "/send", method = RequestMethod.POST)
public String sendEmail(@Valid @ModelAttribute MailSendForm form, BindingResult result, Model model)
{
if (result.hasErrors()) {
model.addAttribute("errorMessage", "error");
return "send";
}
String[] addresses = form.getAddress().split("s*;s*");
boolean isValid = Stream.of(addresses).anyMatch(address -> !Validator.isMailAddress(address));
if (isValid) {
model.addAttribute("errorMessage", "error");
return "send";
}
for (String address : addresses) {
MailInfo mail = new MailInfo("gadget.mailsender@gmail.com", address, form.getSubject(),
form.getBody());
try {
mailService.send(mail);
} catch (Exception e) {
model.addAttribute("errorMessage", "error");
return "send";
}
}
return "send";
}
loc: 18

8. @RequestMapping(value = "/send", method = RequestMethod.POST)
public String sendEmail(@ModelAttribute MailSendForm form, Model model) {
if (!Validator.isSubject(form.getSubject())) {
model.addAttribute("errorMessage", "error");
return "send";
}
if (!Validator.isBody(form.getBody())) {
model.addAttribute("errorMessage", "error");
return "send";
}
String addressFromForm = form.getAddress();
if (StringUtils.isEmpty(addressFromForm)) {
model.addAttribute("errorMessage", "error");
return "send";
}
String[] addresses = addressFromForm.split(";");
for(String address : addresses) {
if (!Validator.isMailAddress(address)) {
model.addAttribute("errorMessage", "error");
return "send";
}
MailInfo mail = new MailInfo("gadget.mailsender@gmail.com", address, form.getSubject(),
form.getBody());
try {
mailService.send(mail);
} catch (Exception e) {
model.addAttribute("errorMessage", "error");
}
}
return "send";
}
loc: 23

9. @RequestMapping(value = "/send", method = RequestMethod.POST)
public String sendEmail(@Valid @ModelAttribute MailSendForm form, BindingResult result, Model model) {
if (result.hasErrors()) {
model.addAttribute("errorMessage", "error");
return "send";
}
String[] addresses = form.getAddress().split(“s*;s*");
boolean isValid = Stream.of(addresses).anyMatch(address -> !Validator.isMailAddress(address));
if (isValid) {
model.addAttribute("errorMessage", "error");
return "send";
}
try {
List<MailInfo> mailInfoList = new ArrayList<>();
String subject = form.getSubject();
for (String address : addresses) {
AddressItem addressItem = addressBookService.findByAddress(address);
if (addressItem != null) {
if (StringUtils.isEmpty(addressItem.getName()) && StringUtils.contains(subject, "$name")) {
throw new Exception("name attribute is empty!!");
}
subject = StringUtils.replace(subject, "$name", addressItem.getName());
}
MailInfo mail = new MailInfo("gadget.mailsender@gmail.com", address, subject, form.getBody());
mailInfoList.add(mail);
}
mailService.sendMultiple(mailInfoList);
} catch (Exception e) {
model.addAttribute("errorMessage", "error");
return "send";
}
return "send";
loc: 26

10. @RequestMapping(value = "/send", method = RequestMethod.POST)
public String sendEmail(@Valid @ModelAttribute MailSendForm form, BindingResult result, Model model) {
if (result.hasErrors()) {
model.addAttribute("errorMessage", "error");
return "send";
}
String[] addresses = form.getAddress().split("s*;s*");
boolean isValid = Stream.of(addresses).anyMatch(address -> !Validator.isMailAddress(address));
if (isValid) {
model.addAttribute("errorMessage", "error");
return "send";
}
try {
List<MailInfo> mailInfoList = new ArrayList<>();
String subject = form.getSubject();
for (String address : addresses) {
AddressItem addressItem = addressBookService.findByAddress(address);
String replacedSubject = subject;
if (addressItem != null) {
if (StringUtils.isEmpty(addressItem.getName()) && StringUtils.contains(subject, "$name")) {
throw new Exception("name attribute is empty!!");
}
replacedSubject = StringUtils.replace(subject, "$name", addressItem.getName());
}else {
if (StringUtils.contains(subject, "$name")){
throw new Exception("email address is not registered");
}
}
MailInfo mail = new MailInfo("gadget.mailsender@gmail.com", address, replacedSubject, form.getBody());
mailInfoList.add(mail);
}
mailService.sendMultiple(mailInfoList);
} catch (Exception e) {
model.addAttribute("errorMessage", "error");
return "send";
}
return "send";
loc: 30

11. @RequestMapping(value = "/send", method = RequestMethod.POST)
public String sendEmail(@Valid @ModelAttribute MailSendForm form, BindingResult result, Model model) {
if (result.hasErrors()) {
FieldError fieldError = result.getFieldErrors().get(0);
model.addAttribute("errorMessage", fieldError.getField() + " " + fieldError.getDefaultMessage());
return "send";
}
String[] addresses = form.getAddress().split("s*;s*");
boolean isValid = Stream.of(addresses)
.anyMatch(address -> !Validator.isMailAddress(address));
if (isValid) {
model.addAttribute("errorMessage", "Email address is invalid");
return "send";
}
try {
List<MailInfo> mailInfoList = new ArrayList<>();
String subject = form.getSubject();
String body = form.getBody();
for (String address : addresses) {
Contact addressItem = addressBookService.findByAddress(address);
String replacedSubject = subject;
String replacedBody = body;
if (addressItem != null) {
if ("".equals(addressItem.getName()) && (subject.contains("$name") || body.contains("$name"))) {
throw new Exception("Can't render template with an empty name in contact");
}
replacedSubject = subject.replace("$name", addressItem.getName());
replacedBody = body.replace("$name", addressItem.getName());
}else {
if (subject.contains("$name") || body.contains("$name")){
throw new Exception("No matching contact found to render template");
}
}
MailInfo mail = new MailInfo("gadget.mailsender@gmail.com", address, replacedSubject, replacedBody);
mailInfoList.add(mail);
}
mailService.sendMultiple(mailInfoList);
} catch (Exception e) {
model.addAttribute("errorMessage", e.getMessage());
return "send";
}
return "send";
}
loc: 33

12. http://www.marketingfirepower.info

13. A NATURE OF SOFTWARE DEVELOPMENT
AMOUNT OF
"BAD” CODE
# BUGS
TIME SPENT
ON FIXING
BUGS
PANIC
QUICK HACKS
MOTIVATION OF
DEVELOPERS
CASUAL LOOP
DIAGRAM

14. A NATURE OF SOFTWARE DEVELOPMENT
REQUIREMENTS
TIME
(you)
(competitor)
COMPETING BY CHANGE

15. The Management of Computer Programming Projects
Charles Lecht - 1967
Equally responsible for the initiation of project with
predefined failure is management that insists upon having
fixed commitments from programming personnel prior to
the latter’s understanding what the commitment are for.
Too frequently, management does not realize that in
asking the staff for “the impossible”, the staff will feel the
obligation to respond out of respect, fear or misguided
loyalty. Saying “no” to the boss frequently requires
courage, political and psychological wisdom, and
business maturity that comes with much experience.

16. A NATURE OF SOFTWARE DEVELOPMENT
AMOUNT OF
"BAD” CODE
# BUGS
TIME SPENT
ON FIXING
BUGS
PANIC
QUICK HACKS
MOTIVATION OF
DEVELOPERS
AMOUNT OF
CODE SMELLS
REFACTORING
OPPORTUNITY FOR
INDICATES

17. REFACTORING 101
SOFTWARE MAINTAINABILITY

18. REFACTORING
“…IS A DISCIPLINED TECHNIQUE FOR
RESTRUCTURING AN EXISTING BODY OF
CODE, ALTERING ITS INTERNAL
STRUCTURE WITHOUT CHANGING ITS
EXTERNAL BEHAVIOR.”
MARTIN FOWLER
INTRODUCE
PARAMETER OBJECT
EXTRACT CLASS
INTRODUCE
LOCAL VARIABLE
RENAME
MOVE METHODEXTRACT METHOD
INLINE VARIABLE

19. Q: WHEN DO WE REFACTOR?
A: WHEN THE CODE SMELLS!

20. CODE SMELLS
“A CODE SMELL IS A SURFACE
INDICATION THAT USUALLY
CORRESPONDS TO A DEEPER PROBLEM
IN THE SYSTEM”
MARTIN FOWLER
DUPLICATED CODE
MAGIC NUMBER
FEATURE ENVY
PRIMITIVE OBSESSION
LONG METHOD
COMMENTS

21. ABOUT DEMO
PERSONALISED EMAILER
WEB APP

22. JAVA
SPRING MVC

24. RECEIVED (NORMAL)
TO: NON-CONTACT@GMAIL.COM
SUBJECT: SEASONS GREETING
TO: NON-CONTACT2@GMAIL.COM
SUBJECT: SEASONS GREETING

27. RECEIVED (TEMPLATE)
TO: STANLY@ODD-E.COM
SUBJECT: SEASONS GREETING STANLY
TO: AKI@ODD-E.COM
SUBJECT: SEASONS GREETING AKI

28. Subject with
attribute
Body with
attribute
Send to
multiple
recipients …
✓ ✓

29. @RequestMapping(value = "/send", method = RequestMethod.POST)
public String sendEmail(@Valid @ModelAttribute MailSendForm form, BindingResult result, Model model) {
if (result.hasErrors()) {
FieldError fieldError = result.getFieldErrors().get(0);
model.addAttribute("errorMessage", fieldError.getField() + " " + fieldError.getDefaultMessage());
return "send";
}
String[] addresses = form.getAddress().split("s*;s*");
boolean isValid = Stream.of(addresses)
.anyMatch(address -> !Validator.isMailAddress(address));
if (isValid) {
model.addAttribute("errorMessage", "Email address is invalid");
return "send";
}
try {
List<MailInfo> mailInfoList = new ArrayList<>();
String subject = form.getSubject();
String body = form.getBody();
for (String address : addresses) {
Contact addressItem = addressBookService.findByAddress(address);
String replacedSubject = subject;
String replacedBody = body;
if (addressItem != null) {
if ("".equals(addressItem.getName()) && (subject.contains("$name") || body.contains("$name"))) {
throw new Exception("Can't render template with an empty name in contact");
}
replacedSubject = subject.replace("$name", addressItem.getName());
replacedBody = body.replace("$name", addressItem.getName());
}else {
if (subject.contains("$name") || body.contains("$name")){
throw new Exception("No matching contact found to render template");
}
}
MailInfo mail = new MailInfo("gadget.mailsender@gmail.com", address, replacedSubject, replacedBody);
mailInfoList.add(mail);
}
mailService.sendMultiple(mailInfoList);
} catch (Exception e) {
model.addAttribute("errorMessage", e.getMessage());
return "send";
}
return "send";
}

30. WHAT DID YOU
SMELL?

31. WHAT DID YOU
SMELL?
L O N G M E T H O D

32. MailController
——————
sendEmail()
MailInfo
AddressBookService
(interface)
———————
findAddress()
MailService
(interface)
——————
sendMultiple()
MailSendForm

33. LET’S REFACTOR
sendEmail()
CODE COVERAGE
✓

34. MailController
——————
sendEmail()
Mail
ContactDao
(interface)
———————
findAddress()
MailService
(interface)
——————
sendMultiple()
EmailTemplate
————-————
populate()
hasPopulateError()
getPopulateErrorMessage()

35. CODE SMELLS
LONG METHOD
TEMPORARY VARIABLE
FEATURE ENVY
DUPLICATE CODE
MAGIC NUMBER
UNCOMMUNICATIVE NAME
PRIMITIVE OBSESSION

36. sendEmail()
BREAKS SINGLE RESPONSIBILITY
MAIL CREATION
ERROR HANDLING
TEMPLATE RENDERING
VALIDITY OF RECIPIENT ADDRESS

37. REFACTORING
EXTRACT METHOD
INLINE VAR. / METHOD
INTRODUCE PARAMETER
RENAME
MOVE METHOD

38. TIPS

39. LEARN TO SMELL
THE CODE
CODE SMELLS

40. DESIGN PRINCIPLES
SINGLE RESPONSIBILITY
HI COHESION, LOW COUPLING

42. while(change_for_new_functionality()){
DO_NOT_REFACTOR()
}

43. PROGRAMMING IS THE ART OF
DOING ONE THING AT A TIME
Michael Feathers
TIPS

44. REFACTORING
WHY? WHAT? HOW?
GET READY
FOR
CHANGE
DESIGN CODE
SMELLS

45. HOW TO START
ESSENTIAL SKILLS
▸ Explain the code with design principles
▸ Identify code smells
▸ Refactor either manually or through IDE
▸ Familiar working with unit/integration tests
▸ Familiar with the functionality you’re changing

46. PRACTICE
REFACTORING KATA
https://github.com/stanlylau/tictactoe_csharp
https://github.com/stanlylau/refactoring-kata
https://github.com/emilybache/Tennis-Refactoring-Kata
https://github.com/emilybache/GildedRose-Refactoring-Kata
https://github.com/stanlylau/trivia-csharp

47. TEACH TO LEARN
1. CREATE CODE SMELLS EXERCISES
2. PRACTICE REMOVING THE SMELLS
3. INVITE PEOPLE TO REMOVE THE SMELLS
4. CODE REVIEW
5. DEMO

48. Unconscious
Competence
Conscious
Competence
Conscious
Incompetence
Unconscious
Incompetence
FOUR STAGES OF COMPETENCE

49. TO LEVEL UP
REVIEW THE CODE WITH A MENTOR,
BE REFLECTIVE

50. EXPERIENCED PROGRAMMERS DO NOT
WRITE INFINITELY COMPLEX CODE;
THEY WRITE CODE THAT’S BLINDINGLY
SIMPLE
99 Bottles of OOP
TIPS

52. REFACTORING IS
AN EXERCISE IN
KINDNESS
Kent Beck

53. THANK YOU
STANLY@ODD-E.COM