1. Refactoring Support Tool: Cancer Yoshiki Higo Osaka University

2. 2 Gemini & Cancer Gemini shows all code clones detected by CCFinder. gives user panoramic views of code clones in source code. has several quantitative information of code clones of each file and clone class. Cancer extracts refactoring-oriented-code clones from ones detected by CCFinder. appends several metric values to extracted code clones. enables user to know how to remove code clones if certain degree of its metric conditions is satisfied.

3. 3 Code clones in Cancer All code clones ( which are extracted from ones detected by CCFinder) correspond to structural blocks of programming language. Currently, Cancer can apply only Java language. Declaration unit code clone class declaration 、 interface declaration Method unit code clone method body 、 constructor 、 static initializer Statement unit code clone do 、 for 、 if 、 switch 、 synchronized 、 try 、 while

4. 4 Metrics in Cancer(1/3) Cancer characterizes extracted code clones using 6 metrics. Using these metrics, we can get how to remove them. 6 metrics are RVK,RVN,DCH,LEN,POP,DFL

5. 5 Metrics in Cancer(2/3) Variables which are used in code clone, but defined outside. 1.RVK : the number of such variables. 2.RVN : the sum of used count of such variables. Relation of code clone on class hierarchy 3.DCH : the degree of dispersion on class hierarchy DCH takes into account only class hierarchy of target software (don ’ t include class hierarchy of library). Class A{ ・・・ } Class B extends A{ ・・・ void foo( ・・・ ){ ・・・ } ・・・ } Class C extends A{ ・・・ void bar( ・・・ ){ ・・・ } ・・・ } code cloneThe value of DCH : 1 Class A{ ・・・ void foo( ・・・ ){ ・・・ } ・・・ void bar( ・・・ ){ ・・・ } ・・・ } code clone The value of DCH : 0 int a; MyClass myClass = new MyClass(); ・・・ for( int i = a ; i < 10 ; i++ ){ int c = a + 1; myClass.set(c); } ・・・ code clone RVK variable The value of RVK : 2 The value of RVN : 2 + 1 = 3

6. 6 Metrics in Cancer(3/3) 4.LEN: the average of length of code clones in a clone class 5.POP: the number of code clones in a clone class 6.DFL: Estimation of how many tokens would be removed from source files when all code clones of a clone class are replaced with caller statements of a new identical routine new sub routine caller statements

7. 7 Removal of Code clone using Refactoring Pattern We use Refactoring Pattern[1] for removal of code clones with 6 metrics Following patterns are applicable. Extract Method Pull Up Method [1] M. Fowler: Refactoring: Improving the Design of Existing Code, Addison-Wesley, 1999.

8. 8 The value of metrics for “ Extract Method ” Target Unit : Method Unit, Statement Unit DCH == 0 RVK <= 1 int i; ・・・ for( int j = 0 ; j < i ; j++ ){ ・・・ } ・・・ int i; ・・・ i = newMethod(i); ・・・ int newMethod(int a){ for( int j = 0 ; j < a ; j++ ){ ・・・ } return a; } ・・・

9. 9 The value of metrics for “ Pull up Method ” Target Unit : Method Unit DCH >= 1

10. 10 ShapShot of Cancer Clone class list Metric Graph clone category selection Panel

11. 11 Specifying code clones User can specify code clones using Metric Graph and Clone Category Selection Panel Metrics Graph : Specifying based on metric values Clone Category Selection Panel : Specifying based on unit of code clone Clone class list shows only specified clone classes

12. 12 Specifying based on metrics values LENPOPDFLRVKRVNDCH

13. 13 Specifying based on unit of code clone LENPOPDFLRVKRVNDCH MethodWhile ・・・・・・・・ ・・・・・ ・・・・・・・ Method UnitWhile Unit

14. 14 Case study Target software : Ant 1.5.4, which is an open source java software. LOC : about 15k The result Using “ Pull up Method ”, 2 clone classes are removed. Using “ Extract Method ”, 1 clone class is removed

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16. 16 Code Clone Code clone is a code fragment in source files that is identical or similar to another Code clone is one of factors that make software maintenance more difficult. If some faults are found in a code clone, it is necessary to consider pros and cons of modification in its all code clones. Clone Pair Clone Class

17. 17 Example Value of RVK, RVN Variables, “ a ” and “ b ” which are used in code clone, but defined outside, are used 2 and 3 times. RVK : 1 + 1 = 2 RVN : 2 + 3 = 5

18. 18 Example values of DCH If all code fragments in a clone class are in same class, DCH : 0 If all code fragments in a clone class are in a certain class and its child classes, DCH : 1 If classes which include code fragments of a certain clone class don ’ t have common parent class, DCH : -1