Abstract. Despite the undisputed prominence of inheritance as the fundamental reuse mechanism in object-oriented programming languages, the main variantssingle inheritance, multiple inheritance, and mixin inheritance -all suffer from conceptual and practical problems. In the first part of this paper, we identify and illustrate these problems. We then present traits, a simple compositional model for structuring object-oriented programs. A trait is essentially a group of pure methods that serves as a building block for classes and is a primitive unit of code reuse. In this model, classes are composed from a set of traits by specifying glue code that connects the traits together and accesses the necessary state. We demonstrate how traits overcome the problems arising from the different variants of inheritance, we discuss how traits can be implemented effectively, and we summarize our experience applying traits to refactor an existing class hierarchy.

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The ubiquity of smartphones, and their very broad capabilities and usage, make the security of these devices tremendously important. Unfortunately, despite all progress in security and privacy mechanisms, vulnerabilities continue to proliferate.Research has shown that many vulnerabilities are due to insecure programming practices. However, each study has often dealt with a specific issue, making the results less actionable for practitioners.To promote secure programming practices, we have reviewed related research, and identified avoidable vulnerabilities in Android-run devices and the security code smells that indicate their presence. In particular, we explain the vulnerabilities, their corresponding smells, and we discuss how they could be eliminated or mitigated during development. Moreover, we develop a lightweight static analysis tool and discuss the extent to which it successfully detects several vulnerabilities in about 46 000 apps hosted by the official Android market.

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