Tech talks#6: Code Refactoring

CODE REFACTORING

Phạm Anh Đới – doipa@fpt.com.vn
Nguyễn Việt Khoa – khoanv4@fpt.com.vn
Hanoi, 11/2011

Code Refactoring – TechTalks #6 2

Objectives
• What’s Code Refactoring?

• Why do we Refactor?

• When should we Refactor?

• How do we Refactor?

• Refactoring Techniques

• Code Refactoring Tools

• Refactoring Dojo


What’s Code Refactoring?

“A series of small steps, each of which changes
the program’s internalstructure without
changing its external behavior “
Martin Fowler


What’s Code Refactoring?
• Code reorganization
o Implies equivalence
o Change the structure, not the behavior
• Cleans up “code-smell”
• Does NOT fix bugs


Why do we Refactor?
• Helps us deliver more business value faster
• Improves the design of our software
• Minimizes technical debt
• Keep development at speed
• To make the software easier to understand
• To help find bugs
• To “Fix broken windows”


Example
Which code segment is easier to read?

Sample 1:
if (markT>=0 && markT<=25 && markL>=0 && markL<=25){
float markAvg = (markT + markL)/2;
System.out.println("Your mark: " + markAvg);
}

Sample 2:
if (isValid(markT) && isValid(markL)){
float markAvg = (markT + markL)/2;
System.out.println("Your mark: " + mark);
}


When should we Refactor?
• To add new functionality
o refactor existing code until you understand it
o refactor the design to make it simple to add
• To find bugs
o refactor to understand the code
• For code reviews
o immediate effect of code review
o allows for higher level suggestions


How do we Refactor?
• Manual Refactoring
o Code Smells
• Automated/Assisted Refactoring
o Refactoring by hand is time consuming and prone to error
o Tools (IDE)
• In either case, test your changes


Code Smell
•Duplicated code • Long Method

• Feature Envy • Long Parameter List

• Inappropriate Intimacy • Switch Statements

• Comments • Improper Naming


Code Smell examples (1)
public void display(String[] names) {
System.out.println(“--------------");
for(int i=0; i<names.length; i++){
System.out.println(“ + " + names[i]);
}
}
Duplicated code
public void listMember(String[] names) {
System.out.println(“List all member: ”);
for(int i=0; i<names.length; i++){
System.out.println(“ + " + names[i]);
}
}


public int getSum() {
Scanner input = new Scanner(System.in);
int[] list = new int[100];
//Input
System.out.println("count:");
int count= input.nextInt();
for (int i= 0; i < count; i++) {
Long Method
list[i] = input.nextInt();
}

//Get sum
int sum=0;
for (int i= 0; i < count; i++) {
sum+=list[i];
}
return sum;
}


public String formatStudent( int id,
String name,
Date dob,
String province,
String address,
Long Parameter List
String phone ){
//TODO:
return null;
}


Refactoring Techniques

• for more abstraction

• for breaking code apart

• for improving code standard


For more abstraction
• Encapsulate Field – force code to access the
field with getter and setter methods
• Generalize Type – create more general types to
allow for more code sharing
• Replace type-checking code with State/Strategy
• Replace conditional with polymorphism


Example
public class Book{
private String title;
public class Book{
String title;
public void setTitle(String title){
if(title!=null){
public title = void main(String[] args) {
static title.trim();
if(!title.isEmpty()){
Book book = new Book();
this.title = title;
}
String title = new Scanner(System.in).nextLine();
}
} if(title!=null){
title = title.trim();
public String getTitle(){
if(!title.isEmpty()){
return title;
} book.title = title;
System.out.println("My book: " + book.title);
public static void main(String[] args) {
}
Book book = new Book();
}
String title = new Scanner(System.in).nextLine();
} book.setTitle(title);
} System.out.println("My book: " + book.getTitle());
}
}


For breaking code apart
• Extract Method, to turn part of a larger method
into a new method. By breaking down code in
smaller pieces, it is more easily understandable.
This is also applicable to functions.
• Extract Class moves part of the code from an
existing class into a new class.


Example
public void showInfor(){
showUser();
showUser();

System.out.println(“Email: “ +
showContact(); email);
} System.out.println(“Phone: “ + phone);
System.out.println(“Address: “ + address);
public void showContact(){
}
System.out.println(“Email: “ + email);
System.out.println(“Phone: “ + phone);
System.out.println(“Address: “ + address);
}


For improving code standard
• Move Method or Move Field – move to a more
appropriate Class or source file
• Rename Method or Rename Field – changing
the name into a new one that better reveals its
purpose
• Pull Up – in OOP, move to a superclass
• Push Down – in OOP, move to a subclass


Example


Tools for Code Refactoring
Supported by IDE
• For Java:
o Netbeans (www.netbeans.org)
o Eclipse (www.eclipse.org)
o IntelliJ IDEA (www.jetbrains.com)
• For .NET:
o Visual Studio (msdn.microsoft.com)
o .NET Refactoring (www.dotnetrefactoring.com)
o JustCode, ReSharper, Visual Assist, …
(addon for Visual Studio)


Refactoring Dojo


Refactoring and TDD

TDD Rhythm - Test, Code, Refactor


Summary
• Improving the design of existing code
• Refactoring does not affect behavior
• The system is also kept fully working after each small
refactoring
• Two general categories of benefits to the activity of
refactoring: Maintainability and Extensibility
• 3 techniques for refactoring
• Using tools for Code Refactoring
• Code Refactoring are often used to improve quality and
enhance project agility.


Q&A


References
•Book: Improving the Design of Existing
Code (by Martin Fowler)
•Sites:
• http://refactoring.com
• http://en.wikipedia.org/wiki/Refactoring
• http://wiki.netbeans.org/Refactoring
• http://msdn.microsoft.com/en-
us/library/ms379618(v=vs.80).aspx


Thank you
doipa@fpt.com.vn – khoanv4@fpt.com.vn

Tech talks#6: Code Refactoring

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