Improving energy-efficiency by recommending Java collections


Over the last years, increasing attention has been given to creating energy-efficient software systems. However, developers still lack the knowledge and the tools to support them in that task. In this work, we explore our vision that non-specialists can build software that consumes less energy by alternating diversely-designed pieces of software without increasing the development complexity. To support our vision, we propose an approach for energy-aware development that combines the construction of application-independent energy profiles of Java collections and static analysis to produce an estimate of in which ways and how intensively a system employs these collections. We implement this approach in a tool named CT+ that works with both desktop and mobile Java systems and is capable of analyzing 39 different collection implementations of lists, maps, and sets. We applied CT+ to seventeen software systems: two mobile-based, twelve desktop-based, and three that can run in both environments. Our evaluation infrastructure involved a high-end server, two notebooks, three smartphones, and a tablet. Overall, 2295 recommendations were applied, achieving up to 16.34% reduction in energy consumption, usually changing a single line of code per recommendation. Even for a real-world, mature system such as Tomcat, CT+ could achieve a 4.12% reduction in energy consumption. Our results indicate that some widely used collections, e.g., ArrayList, HashMap, and Hashtable, are not energy- efficient and sometimes should be avoided when energy consumption is a major concern.

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    EU guidelines:

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    Available at:

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    On our experiments, the threshold was 100 times slower


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We would like to thank the anonymous reviewers for helping to improve this paper. This paper acknowledges the support of the Erasmus+ Key Action 2 (Strategic partnership for higher education) project No. 2020-1-PT01-KA203-078646: ”SusTrainable - Promoting Sustainability as a Fundamental Driver in Software Development Training and Education”. The information and views set out in this paper are those of the author(s) and do not necessarily reflect the official opinion of the European Union. Neither the European Union institutions and bodies nor any person acting on their behalf may be held responsible for the use which may be made of the information contained therein. This research was partially funded by CAPES/Brazil (88887.364121/2019-00), CNPq/Brazil (304755/2014-1, 406308/2016-0, 465614/2014-0, 309032/2019-9), FACEPE/Brazil (APQ-0839-1.03/14, 0388-1.03/14, 0592-1.03/15).

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This article belongs to the Topical Collection: Recommendation Systems for Software Engineering

Communicated by: Ali Ouni, David Lo, Xin Xia, Alexander Serebrenik and Christoph Treude

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Oliveira, W., Oliveira, R., Castor, F. et al. Improving energy-efficiency by recommending Java collections. Empir Software Eng 26, 55 (2021).

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  • Energy consumption
  • Collections
  • Recommendation systems