The document discusses refactoring code to improve maintainability. It defines refactoring as restructuring existing code without changing external behavior. The key points are: 1) Refactoring helps deal with the natural growth of complexity in software development by improving flexibility. It reduces bugs and time spent fixing bugs. 2) Common code smells that indicate an opportunity for refactoring are duplicated code, magic numbers, feature envy, primitive obsession, and long methods. 3) Practicing refactoring through katas and dojos on production code is recommended to learn essential skills like identifying code smells and applying refactoring techniques while preserving functionality. 4) Following principles like single responsibility and high cohesion

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

2. INTRODUCTION
ABOUT ME
▸ Lives in Singapore
▸ Software development
coach / mentor
▸ Lead Agile Singapore
community

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

4. @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

5. @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

6. @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

7. @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

8. @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

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);
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

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();
String body = form.getBody();
for (String address : addresses) {
String replacedSubject = subject;
String replacedBody = body;
if (StringUtils.contains(subject, "$name") || StringUtils.contains(body, "$name")) {
AddressItem addressItem = addressBookService.findByAddress(address);
if (addressItem == null) {
throw new Exception("email address is not registered");
}
if (StringUtils.isEmpty(addressItem.getName())) {
throw new Exception("name attribute is empty!!");
}
replacedSubject = StringUtils.replace(subject, "$name", addressItem.getName());
replacedBody = StringUtils.replace(body, "$name", addressItem.getName());
}
MailInfo mail = new MailInfo("gadget.mailsender@gmail.com", address, replacedSubject, replacedBody);
mailInfoList.add(mail);
}
mailService.sendMultiple(mailInfoList);
} catch (Exception e) {
model.addAttribute("errorMessage", "error");
return "send";
}
return "send";
}
loc: 32

11. DEVELOPERS GET BETTER AT
COMPLEXITY AND SOMETIMES
THEY BELIEVE IT IS INEVITABLE.

12. EXPERIENCED PROGRAMMERS DO NOT
WRITE INFINITELY COMPLEX CODE;
THEY WRITE CODE THAT’S BLINDINGLY
SIMPLE
99 Bottles of OOP
GROWTH OF A DEVELOPER

13. THE NATURE OF SOFTWARE DEVELOPMENT
LEARNING THIS NATURE
AND DEALING WITH IT
HELPS TO INCREASE
FLEXIBILITY.
AMOUNT OF
BAD CODE
# BUGS
TIME SPENT
ON FIXING
BUGS
PANIC
QUICK HACKS
MOTIVATION OF
DEVELOPERS
REFACTORING
AMOUNT OF
CODE SMELLS
INDICATES
OPPORTUNITY FOR

14. IRONICALLY, DEVELOPERS
ARE TOLD TO DO MORE

15. WHAT CAN HELP?
SOFTWARE MAINTAINABILITY

16. 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

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

18. 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

19. DEMO
PERSONALISED EMAILER
WEB APP

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

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

25. DESIGN DIRECTION
BRING OUT TEMPLATE
CONCEPT

26. HOW TO START

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

28. TRY CODING DOJO SESSIONS
ON PRODUCTION CODE
PICK CODE SMELLS TO REMOVE

29. LEARN TO SMELL
THE CODE
CODE SMELLS

30. 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

31. DESIGN PRINCIPLES
SINGLE RESPONSIBILITY
HI COHESION, LOW COUPLING

33. 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

34. CRAFTSMANSHIP

35. REFACTORING IS
AN EXERCISE IN
KINDNESS
Kent Beck

36. THANK YOU
STANLY@ODD-E.COM