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Code refactoring using eclipse

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  • 1. 用 Eclipse 重構程式碼Code Refactoring Using Eclipse 中華電信 黃培棠 beta@cht.com.tw 2013/02/26
  • 2. WHAT IS REFACTORING? 2
  • 3. 2 𝑥 − 1 = 𝑥 + 1 (𝑥 − 1) Factoring: 因式分解參考資料: http://zh.wikipedia.org/zh-tw/代碼重構 3
  • 4. 2 𝑥 −1 不影響外部行為 2 = 𝑥 − 𝑥+ 𝑥−1 = 𝑥 𝑥−1 + 𝑥−1 = 𝑥 + 1 (𝑥 − 1)循序漸進, Re- 4
  • 5. 怎麼證明?• Given f x = 𝑥 2 − 1 – We know that f 3 = 8• 單元測試 3A 原則: – Arrange: f 3 = 8, f′ x = 𝑥 + 1 𝑥 − 1 – Act: f ′ 3 = 3 + 1 3 − 1 = 4 × 2 = 8 – Assert: f 3 = f ′ (3) 數學家看了可能會搖頭, 還好我們是 Programmer! 5
  • 6. 重構前… 重構後… 重構是 Programmer 自爽的事? 6
  • 7. Refactoring 定義 • Refactoring (名詞) – A change made to the internal structure of software to make it easier to understand and cheaper to modify without changing its observable behavior. • 除非你想參加 OMG WTF http://thedailywtf.com/Articles/The-Worse-Than-Failure-Programming-Contest.aspx“Refactoring: Improving the Design of Existing Code”, Martin Fowler, Kent Beck, et al., 1999 7
  • 8. Any fool can write code that a computer can understand. Good programmers write code that humans can understand. - Martin Fowler“Refactoring: Improving the Design of Existing Code”, Martin Fowler, Kent Beck, et al., 1999 8
  • 9. WHEN TO REFACTORING? 9
  • 10. 重構的好時機• 一樣的事做到第三次時• 按下「貼上」前• 要新增功能時• 開始修 Bug 前• Code Review 時 10
  • 11. If it stinks, change it. —Grandma Beck, discussing child-rearing philosophy“Refactoring: Improving the Design of Existing Code”, Martin Fowler, Kent Beck, et al., 1999 11
  • 12. 重構標的 — Code Smells Within Classes Between Classes • Comments • Primitive Obsession • Long Method • Data Clumps • Long Parameter List • Refused Bequest • Duplicated Code • Indecent Exposure • Conditional Complexity • Feature Envy • Large Class • Lazy Class • Uncommunicative Name • Divergent Change • Dead Code • Shotgun Surgery • … • …http://www.codinghorror.com/blog/2006/05/code-smells.html, Coding Horror: Code Smells, May 18. 2006 12
  • 13. 怎麼跟老闆講?• 不用講,做就對了• 重視品質的老闆 – 他會懂你的• 嘴巴說重視品質的老闆 – 說了也是白說 – 你真的是在幫他 – The fastest way is to refactor; therefore I refactor. – Martin Fowler 13
  • 14. 什麼時候該停手 • 程式該砍掉重練時 // When I wrote this, only God and I understood what I was doing // Now, God only knows • Deadline 前夕 • 夠好了,對你自己、客戶、還有下個_____ – 明天會更好 – Striving to better, oft we mar what’s well. – “King Lear” 1.4, William Shakespeare – Good-Enough Software, “The Pragmatic Programmer”, Andy Hunt, David Thomashttp://stackoverflow.com/questions/184618/what-is-the-best-comment-in-source-code-you-have-ever-encountered 14
  • 15. REFACTORING USING ECLIPSE 15
  • 16. Coding Style• 確定團隊整體的 Code Style Formatter – 養成常 [Ctrl] + [Shift] + [F] 的習慣• 輔助確認格式 – 以 eclipse-cs 輔助確認 • 同樣要先定義好 Checkstyle 的 Rule – 統一使用 AnyEdit Tools 外掛程式 – 在版本管理系統上面掛 pre-commit hook 16
  • 17. 移除 Dead Code • // Don’t do this! // There was a time, back in the sixties, when // commenting-out code might have been useful. • // Nowadays, just delete the code // We won’t lose it. Promise. // Revision control system will remember it.“Clean Code: A Handbook of Agile Software Craftsmanship”, Robert C. Martin, August 2008 17
  • 18. 移除 Dead Code • Visibility 要盡可能低 – public > protected > package private > private public void whyNoOneCallsMe() { // Why am I so useless, how can I not be? } private void whyNoOneCallsMe() { // Why am I so useless, how can I not be? }http://sourcemaking.com/implementation-patterns/method-visibility, Method Visibility 18
  • 19. Dead Code 移除小技巧• 注意 Reduce Visibility 可能的風險 – 介面已經昭告天下時只能 @Deprecated• Dead Code 不見得都那麼好發現 – 不可能跑到的 if else 或 switch case 區塊 – 請 PMD, FindBugs 幫忙• 開始用其他重構技巧吧! – 讓原本的程式更好懂、好修改。 19
  • 20. Eclipse 1.0 (Nov 2001)圖片提供: https://twitter.com/jiayun 20
  • 21. Eclipse 2.0 (Jun 2002)圖片提供: https://twitter.com/jiayun 21
  • 22. Eclipse 2.1 (Mar 2003)圖片提供: https://twitter.com/jiayun 22
  • 23. Eclipse 3.7 (Jun 2011) 圖片提供: https://twitter.com/jiayun 23
  • 24. Rename• 使用時機 – 看到不順眼或是無法會意的名字 – 有病治病,沒病強身• 命名原則 – 簡單明瞭 – 符合 Naming Convention (由 Coding Style 規範) • 例如: getRgbHex(Colors.SNOW_WHITE) 24
  • 25. Rename 注意事項• 要保留住檔案修訂歷程 – 裝好 Eclipse Team Provider 再改名 – 否則請用 SCM Client 提供的改名功能 25
  • 26. Rename 小技巧• 開 Mark Occurrences 功能 OutputStream os = new FileOutputStream("test.txt"); try { os.write("test".getBytes()); } finally { os.close(); }• Method 改名可用 Change Method Signature – 如果介面已經公開,請勾 “Keep original method as delegate to changed method” 選項 26
  • 27. 改名參數名稱、順序也能改 維護 相容性 27
  • 28. Extract Local Variable• 使用時機 – 一行程式串太長 new BufferedOutputStream( new FileOutputStream("test.txt")); – 發現對同一個資料物件重複取值 authorties = repository.queryAuthorities(user.getName()); LOGGER.debug("User {} authenticated.", user.getName()); 28
  • 29. Eclipse 會幫你做的事 重構 結果 29
  • 30. Extract Local Variable 注意事項 • Variable 的 Scope 一樣是越小越好 – 一般就是 Local Variable 被 Extract 出來的位置 – 使用 [Alt] + [↑]/[↓] 可以調整 int value = getTheAnswerToTheUltimateQuestion(); Result result = new Result(); // <= 要用到再宣告 result.setValue(value); return result; • Extract 過頭怎麼辦? – Inline 是 Extract Local Variable 的 inverse。http://www.refactoring.com/catalog/reduceScopeOfVariable.html, Reduce Scope of Variable 30
  • 31. Extract Local Variable 偷吃步• 宣告變數並給值少打字 – 直接寫右邊的內容 – 讓 Eclipse 幫你把左邊的宣告補起來 encrypt(data, certificate); [Alt] + [Shift] + [L] EncyptionResult result = encrypt(data, certificate); 31
  • 32. Extract Method• 使用時機 – Method 內容過長,超過螢幕能顯示的範圍 – 很想幫 Method 裡某個區塊加註解時• Method 設計原則 – 名稱符合 Coding Style – 參數數量不要太多或是型別重複 32
  • 33. // 取憑證X509Certificate certificate;try { String base64Cert = certificateRepository.queryMoicaCertificate user.getUserId(), user.getName(), user.getCounty()); certificate = CertificateUtils.generateCertificate(base64Cert);} catch (CmsException e) { throw new CmsEncryptionException(e.getMessage(), e);}// 資料加密EncyptionResult result = encrypt(data, certificate); // 取憑證X509Certificate certificate = retrieveCertificates(user);// 資料加密EncyptionResult result = encrypt(data, certificate); 33
  • 34. Method 參數長相是關鍵• 先 Extract Local Variable,讓 Method 更精確 notifyUser(User user); String userId = user.getId(); notifyUser(String userId);• 往前多選到 Variable,讓新 Method 更簡單 String userId = user.getId(); notifyUser(String userId); notifyUser(User user); 34
  • 35. Extract Method 偷吃步• Method 規畫方式 1. 能先想清楚最好 2. 不然先定義參數物件,再慢慢修改其 Property 3. 如果剛好今天沒帶腦,就先寫成一坨,再 Extract Method 出來• 使用大忌: 不要為了 Extract 而 Extract – 雖然犯錯了一樣可以 Inline 回去 35
  • 36. Extract Interface • 使用時機 – 發現兩個物件的行為有點像時 – 很謙虛,不想暴露太多面向的資訊給使用端時 – 有特別的情感因素時http://sourcemaking.com/refactoring/extract-interface, Extract Interface 36
  • 37. Extract Interface 注意事項• 使用 Interface 好處多,不過也是有代價的 – 現在 Spring Framework, Mockito… 都能簡單處理 Class,不是非 Interface 不可• 不用先定義好 Interface – 除非你正在設計要公開的 API – 用到再做都還不遲 37
  • 38. 繼承結構調整• Extract Superclass – 跟 Extract Interface 有點像,但是包含 Filed 及 Method 實作• Pull Up – 將 Member 往上層提 (Generalization)• Push Down – 跟 Pull Up 相反 (Specialization) 38
  • 39. 繼承結構調整 注意事項• 不是什麼都該繼承來 – 有時候用別人家的更划算! (改用 Composite) – 想清楚到底是 Is-A 或是 Has-A 39
  • 40. Introduce Parameter Object• 使用時機 – Method 參數過多 (4, 5 個就算不少了) – Method 參數中有相同的型別• 範例: getColorName(int red, int green, int blue); getColorName(Color color); color.getName() 40
  • 41. Extract Class• 跟 Introduce Parameter Object 異曲同工• Extract Class 的對象是 Class 裡的 Field public class Employee { private String name; private String officeAreaCode; private String officeNumber; } public class Employee { private String name; private PhoneNumber officeTel; } public class PhoneNumber { private String areaCode; private String number; 41 }
  • 42. Extract Class 小技巧• 同時選取多個 Class 可以提出共用的 Fieldpublic class Employee { public class Outsourcer { private String name; private String contractId; private String officeAreaCode; private String officeAreaCode; private String officeNumber; private String officeNumber;} }public class Employee { public class Outsourcer { private String name; private String contractId; private PhoneNumber officeTel; private PhoneNumber officeTel;} } public class PhoneNumber { private String areaCode; private String number; } 42
  • 43. Try to leave this worlda little better than you found it. – Baden-Powell 43
  • 44. REFERENCES 44
  • 45. 參考資料• “Refactoring: Improving The Design of Existing code”, Martin Fowler, Kent Beck, John Brant, William Opdyke, and Don Roberts, 1999• Code Smells - Jeff Atwood – http://www.codinghorror.com/blog/2006/05/code- smells.html• Web 程式重構 – Jace Ju – http://www.slideshare.net/jaceju/web-1494836 45
  • 46. 延伸閱讀• 如何成為更好的 PHP 開發者 – Jace Ju – https://speakerdeck.com/jaceju/how-to-be-a-better- php-developer• 27 inspiring top notch programming quotes – http://www.marcofolio.net/tips/27_inspiring_top_n otch_programming_quotes.html 46
  • 47. 可參考的書籍• “Refactoring: Improving The Design of Existing code”, Martin Fowler, Kent Beck, John Brant, William Opdyke, and Don Roberts, 1999 – 《重構 – 改善既有程式的設計 第二版》 侯捷、熊節 譯 – http://sourcemaking.com/refactoring• “Refactoring to Pattterns”, Joshua Kerievsky, 2004 – 《重構 – 向範式前進》侯捷、陳裕城 譯• “Java言語で学ぶ リファクタリング入門”, 結城 浩, 2007 – 《Java 重構》江珮齡、王元綱、博碩文化 譯 47