CODE REFACTORING

Phạm Anh Đới – doipa@fpt.com.vn Nguyễn Việt Khoa – khoanv4@fpt.com.vn

Hanoi, 11/2011

TechTalks #6

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Objectives

• What’s Code Refactoring?

• Why do we Refactor?

• When should we Refactor?

• How do we Refactor?

• Refactoring Techniques

• Code Refactoring Tools

• Refactoring Dojo

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What’s Code Refactoring?

“A series of small steps, each of which changes

the program’s internal structure without

changing its external behavior “

Martin Fowler

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What’s Code Refactoring?

• Code reorganization

o Implies equivalence

o Change the structure, not the behavior

• Cleans up “code-smell”

• Does NOT fix bugs

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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”

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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);

}

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When should we Refactor?

• To add new functionalityo refactor existing code until you understand ito refactor the design to make it simple to add

• To find bugso refactor to understand the code

• For code reviewso immediate effect of code reviewo allows for higher level suggestions

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How do we Refactor?

• Manual Refactoringo Code Smells

• Automated/Assisted Refactoringo Refactoring by hand is time consuming and prone to erroro Tools (IDE)

• In either case, test your changes

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Code Smell

•Duplicated code

• Feature Envy

• Inappropriate Intimacy

• Comments

• Long Method

• Long Parameter List

• Switch Statements

• Improper Naming

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Code Smell examples (1)

Code Refactoring – TechTalks #6

public void display(String[] names) { System.out.println(“--------------"); for(int i=0; i<names.length; i++){

System.out.println(“ + " + names[i]); }System.out.println(“--------------");

}

public void listMember(String[] names) { System.out.println(“List all member: ”);System.out.println(“--------------"); for(int i=0; i<names.length; i++){

System.out.println(“ + " + names[i]); }System.out.println(“--------------");

}

Duplicated code

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Code Smell examples (2)

Code Refactoring – TechTalks #6

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++) { list[i] = input.nextInt(); }

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

Long Method

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Code Smell examples (3)

Code Refactoring – TechTalks #6

public String formatStudent( int id, String name, Date dob,String

province, String address, String phone ){

//TODO:return null;

}

Long Parameter List

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Refactoring Techniques

• for more abstraction

• for breaking code apart

• for improving code standard

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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

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Example

public class Book{ String title;

public static void main(String[] args) { Book book = new Book();

String title = new Scanner(System.in).nextLine();

if(title!=null){title = title.trim();

if(!title.isEmpty()){book.title = title;System.out.println("My book: " +

book.title); }

}}

}

public class Book{ private String title;

public void setTitle(String title){ if(title!=null){

title = title.trim();if(!title.isEmpty()){

this.title = title; }

} }

public String getTitle(){return 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());

} }

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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.

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public void showInfor(){showUser();

System.out.println(“Email: “ + email);System.out.println(“Phone: “ + phone);System.out.println(“Address: “ + address);

}

Examplepublic void showInfor(){

showUser();

showContact();}

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

}

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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

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Example

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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)

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Refactoring Dojo

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Refactoring and TDD

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TDD Rhythm - Test, Code, Refactor

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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.

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Q & A

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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

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Thank you

Code Refactoring – TechTalks #6

doipa@fpt.com.vn – khoanv4@fpt.com.vn