Towards an Assessment of the Quality of Refactoring Patterns Norihiro Yoshida, Masatomo Yoshida, Katsuro Inoue Osaka University, Japan Department of Computer Science, Graduate School of Information Science & Technology, Osaka University 1 Refactoring Refactoring is a process of restructuring an existing code. software’s internal structure without changing its external behavior Improve the maintainability of software Alter Example of Refactoring Merging code clones into a new method New method Call statements Department of Computer Science, Graduate School of Information Science & Technology, Osaka University 2 Refactoring Pattern Typical process of restructuring existing code Extract Method, Pull Up Method, Extract Class Each refactoring pattern includes refactoring a set of code fragments that should be refactored procedure opportunity (bad smell) to perform refactoring how to perform refactoring Department of Computer Science, Graduate School of Information Science & Technology, Osaka University 3 Literatures for Refactoring Patterns A lot of refactoring patterns are proposed in several literatures. M. Fowler, Refactoring: improving the design of existing code. Addison Wesley, 1999. M. Fowler, http://refactoring.com/ (93 patterns) J. Kerievsky, Refactoring to Patterns. Addison Wesley, 2004. (27 patterns) However, the quality of each refactoring pattern is mostly never assessed. Department of Computer Science, Graduate School of Information Science & Technology, Osaka University 4 Overview of Our Research Propose the following quality characteristics of refactoring patterns Number of Refactoring Opportunities Ease of Refactoring Perform a case study on assessing those quality characteristics A case study on Introduce Polymorphic Creation with Factory Method [1] that is a kind of Pull Up Method Department of Computer Science, Graduateto School of InformationAddison Science & Technology, Osaka University [1] J. Kerievsky, Refactoring Patterns. Wesley, 2004 5 Propose Quality Characteristics of Refactoring Patterns Number of Refactoring Opportunities What kind of refactoring opportunities are involved in software systems? Ease of Refactoring It means that ease of applying each refactoring pattern to refactoring opportunities in source code. We focus on “Whether or not each refactoring pattern involves enough description to perform refactoring easily”. Department of Computer Science, Graduate School of Information Science & Technology, Osaka University 6 Case Study Target Refactoring Pattern (1/2) We assess the quality characteristics of Introduce Polymorphic Creation with Factory Method. Before Refactoring junit::framework::TestCase Condition 1 DOMBuilderTest XMLBuilderTest testAddAboveRoot testAddAboveRoot Similar methods belong to classes that have a common parent class. Condition 2 ・・・ builder = new DOMBuilder(…); ・・・ Only difference among similar methods is an object creation step. ・・・ builder = new XMLBuilder(…); ・・・ Department of Computer Science, Graduate School of Information Science & Technology, Osaka University 7 Case Study Target Refactoring Pattern (2/2) We assess the quality characteristics of Introduce Polymorphic Creation with Factory Method. Before Refactoring After Refactoring junit::framework::TestCase junit::framework::TestCase AbstractBuilderTest #builder: OutputBuilder DOMBuilderTest XMLBuilderTest testAddAboveRoot It’s easy to addtestAddAboveRoot new test class. ・・・ builder = new DOMBuilder(…); ・・・ ・・・ builder = new XMLBuilder(…); ・・・ createBuilder testAddAboveRoot Factory Method: Creator ・・・ builder = new createBuilder(“orders”); ・・・ Factory Method: ConcreteCreator DOMBuilderTest XMLBuilderTest createBuilder createBuilder return new DOMBuilder(…); return new XMLBuilder(…); Department of Computer Science, Graduate School of Information Science & Technology, Osaka University 8 Case Study Automation of Identifying Opportunities We developed an automated tool that identifies opportunities. Condition 1 Before Refactoring junit::framework::TestCase Similar methods belong to classes that have a common parent class. Step 1 DOMBuilderTest XMLBuilderTest testAddAboveRoot testAddAboveRoot Detect similar methods using a code clone detection tool CCFinder Condition 2 ・・・ builder = new DOMBuilder(…); ・・・ ・・・ builder = new XMLBuilder(…); ・・・ Only difference among similar methods is an object creation step. Step 2 Evaluate whether detected methods include object creation statements Department of Computer Science, Graduate School of Information Science & Technology, Osaka University 9 Case Study Number of Refactoring Opportunities Target LOC # classes # opportunities Target Pattern for Pull UpUp Method 17.9% of the refactoring opportunities Pull ANTLR 1 Method are 32K also for 167 Introduce Polymorphic Creation33 Ant 198K 2 23 with Factory Method.994 Azureus 538K 2226 20 42 jEdit 168K 922 0 1 JHotDraw 487 1 26 Developers 90K should inspect whether refactoring SableCC 35K 0 opportunities for Pull237 Up Method are also are also 1 Soot 352K 2298 5 Factory for Introduce Polymorphic Creation with 53 Method. WALA 22 210K 1565 7 Department of Computer Science, Graduate School of Information Science & Technology, Osaka University 10 Case Study Ease of Refactoring 1. 2. Apply the target pattern to the refactoring opportunities in Ant and ANTLR. Confirm the steps that are not described in the description of the target pattern. We did not have to apply additional steps that are not described in the description of the target pattern. In terms of the ease of refactoring, the quality of the pattern presentation is enough. Department of Computer Science, Graduate School of Information Science & Technology, Osaka University 11 Summary & Future Work Summary Two quality characteristics of refactoring patterns A case study on assessing those quality characteristics Future Work Assess other refactoring patterns To compare refactoring patterns in terms of proposed quality characteristics Discuss change in maintainability Department of Computer Science, Graduate School of Information Science & Technology, Osaka University 12
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