Identification of Refused Bequest Code Smells E. Ligu, A. Chatzigeorgiou, T. Chaikalis, N. Ygeionomakis Department of Applied Informatics University of Macedonia, Greece ICSM’2013, Early Research Achievements Track, September 24, 2013

Context In the world of OO systems, inheritance is not a panacea Mammal + breatheAir() + regulateBodyTemp() + giveBirthToLiveYoung() + produceMilkIfFemale() + swim() + breatheAir() + regulateBodyTemp() + giveBirthToLiveYoung() + produceMilkIfFemale() + swim() + breatheAir() + regulateBodyTemp() + giveBirthToLiveYoung() + produceMilkIfFemale() + swim()

Problem Goal: Identification of Refused Bequest Code Smells Refused Bequest: “a subclass does not want to support the interface inherited from its parent class” [Fowler] non-trivial problem to resolve Appropriate Refactoring: Replace Inheritance with Delegation Famous quote: “Favor Composition over Inheritance” [GoF]

Key Concept public interface which is inherited is the subclass using the inherited interface? OK indication of Refused Bequest

Smell Thermometer Refused Bequest is highly improbable: -inherited methods have been re- implemented to provide functionality that is specific to the subclass -> goal is to enable polymorphism. -the presence of errors -> inherited functionality is actually employed. Signs of Refused Bequest : -no superclass method is overridden -no inherited method is invoked on subclass instances -no super class method invocations No argument in favor of inheritance

Example SweetHome 3D v.4.0 LOC: 76K, 460 classes, 69 hierarchies, 42 test cases

Tool Implementation on top of the JDeodorant tool

Threat to Validity Assumption: unit tests exercise thoroughly system functionality Threat to construct validity: introduced errors might not lead to test failures because tests have not been designed to cause the invocation of the corresponding methods and not because the methods are not actually utilized. Mitigation: perform identification on projects with extensive test coverage

Question 1 (academic): Would you trust an automated tool to identify and resolve design defects on its own? Question 2 (provocative): Do you think that industrial engineers actually regard the resolution of smells as a (serious) way to improve the code? ICSM’2013, Early Research Achievements Track, September 24, 2013