Inheritance versus Delegation: Which is more energy efficient?

Abstract

Energy consumption of software is receiving more attention as concerns regarding climate change increase. One factor that significantly impacts how much energy is expended by a software application is the design of the software itself. Existing studies find few consistent results regarding the impact of common refactorings on energy consumption, nor do they define a concrete set of metrics that measure the energy efficiency of software. In this paper, we present the results of preliminary experiments that explore the Replace Inheritance with Delegation refactoring, and its inverse, to assess the impact these design-level refactorings have on energy consumption in the Java programming language. In the tested programs, inheritance proved to be more energy efficient than delegation, with a reduction in run time of 77% and a reduction in average power consumption of 4%. We subsequently propose a research plan to further explore this problem and observe a number of specific challenges in this area. The primary goals of this research are threefold: (i) to investigate how redundancy in an object-oriented design can contribute to unnecessary energy consumption, (ii) to determine how refactoring of the software can remove this redundancy, and (iii) to develop a general-purpose automated tool to perform this refactoring.