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Tech talks#6: Code Refactoring

  1. 1. CODE REFACTORING Phạm Anh Đới – doipa@fpt.com.vn Nguyễn Việt Khoa – khoanv4@fpt.com.vn Hanoi, 11/2011
  2. 2. 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
  3. 3. Code Refactoring – TechTalks #6 3 What’s Code Refactoring? “A series of small steps, each of which changes the program’s internalstructure without changing its external behavior “ Martin Fowler
  4. 4. Code Refactoring – TechTalks #6 4 What’s Code Refactoring? • Code reorganization o Implies equivalence o Change the structure, not the behavior • Cleans up “code-smell” • Does NOT fix bugs
  5. 5. Code Refactoring – TechTalks #6 5 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”
  6. 6. Code Refactoring – TechTalks #6 6 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); }
  7. 7. Code Refactoring – TechTalks #6 7 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
  8. 8. Code Refactoring – TechTalks #6 8 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
  9. 9. Code Refactoring – TechTalks #6 9 Code Smell •Duplicated code • Long Method • Feature Envy • Long Parameter List • Inappropriate Intimacy • Switch Statements • Comments • Improper Naming
  10. 10. Code Refactoring – TechTalks #6 10 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]); } System.out.println(“--------------"); } Duplicated code 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(“--------------"); }
  11. 11. Code Refactoring – TechTalks #6 11 Code Smell examples (2) 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; }
  12. 12. Code Refactoring – TechTalks #6 12 Code Smell examples (3) public String formatStudent( int id, String name, Date dob, String province, String address, Long Parameter List String phone ){ //TODO: return null; }
  13. 13. Code Refactoring – TechTalks #6 13 Refactoring Techniques • for more abstraction • for breaking code apart • for improving code standard
  14. 14. Code Refactoring – TechTalks #6 14 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
  15. 15. Code Refactoring – TechTalks #6 15 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()); } }
  16. 16. Code Refactoring – TechTalks #6 16 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.
  17. 17. Code Refactoring – TechTalks #6 17 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); }
  18. 18. Code Refactoring – TechTalks #6 18 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
  19. 19. Code Refactoring – TechTalks #6 19 Example
  20. 20. Code Refactoring – TechTalks #6 20 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)
  21. 21. Code Refactoring – TechTalks #6 21 Refactoring Dojo
  22. 22. Code Refactoring – TechTalks #6 22 Refactoring and TDD TDD Rhythm - Test, Code, Refactor
  23. 23. Code Refactoring – TechTalks #6 23 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.
  24. 24. Code Refactoring – TechTalks #6 24 Q&A
  25. 25. Code Refactoring – TechTalks #6 25 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
  26. 26. Code Refactoring – TechTalks #6 26 Thank you doipa@fpt.com.vn – khoanv4@fpt.com.vn

Editor's Notes

  • Nguồn tham khảo: Java Refactoring Fest (presentation) - Naresh Jain - naresh@agilefaqs.comhttp://refactoring.comRefactoring workbook - William C. WakeRefactoring to Patterns - Joshua KerievskyRefactoring (presentation) - Jason Lee
  • Improves the design of our softwareLoại bỏ những code tồiGiúp code dễ hiểu và dễ bảo trìTạo điều kiện thuận lợi cho các thay đổiTăng tính linh hoạtTăng khả năng tái sử dụng
  • Cầncóvídụ
  • Mỗikỹthuậtcầncómột demo
  • Giới thiệu về một thiết kế (tồi) biểu diễn với UML trênĐới + Khoa (5 phút): thiết kế lại (đồng thời)So sánh 2 bản thiết kế mới của Đới và Khoa với bản ban đầuCùng sinh viên thảo luận, đánh giáDùng Netbeans triển khai theo thiết kế ban đầu và dùng các kỹ thuật Refactor có sẵn của Netbeans để thực hiện Refactor theo 2 bản thiết kế mới
  • Ảnh từ: Slide của Naresh Jain
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