Abstract-This paper reports on a study mining the exception stack traces included in 159,048 issues reported on Android projects hosted in GitHub (482 projects) and Google Code (157 projects). The goal of this study is to investigate whether stack trace information can reveal bug hazards related to exception handling code that may lead to a decrease in application robustness. Overall 6,005 exception stack traces were extracted, and subjected to source code and bytecode analysis. The outcomes of this study include the identification of the following bug hazards: (i) unexpected cross-type exception wrappings (for instance, trying to handle an instance of OutOfMemoryError "hidden" in a checked exception) which can make the exceptionrelated code more complex and negatively impact the application robustness; (ii) undocumented runtime exceptions thrown by both the Android platform and third party libraries; and (iii) undocumented checked exceptions thrown by the Android Platform. Such undocumented exceptions make difficult, and most of the times infeasible for the client code to protect against "unforeseen" situations that may happen while calling third-party code. This study provides further insights on such bug hazards and the robustness threats they impose to Android apps as well as to other systems based on the Java exception model.

Adequate handling of exceptions has proven difficult for many software engineers. Mobile app developers in particular, have to cope with compatibility, middleware, memory constraints, and battery restrictions. The goal of this paper is to obtain a thorough understanding of common exception handling bug hazards that app developers face. To that end, we first provide a detailed empirical study of over 6,000 Java exception stack traces we extracted from over 600 open source Android projects. Key insights from this study include common causes for system crashes, and common chains of wrappings between checked and unchecked exceptions. Furthermore, we provide a survey with 71 developers involved in at least one of the projects analyzed. The results corroborate the stack trace findings, and indicate that developers are unaware of frequently occurring undocumented exception handling behavior. Overall, the findings of our study call for tool support to help developers understand their own and third party exception handling and wrapping logic.

A elaboração de material didático para a educação a distância, da teoria a prática: um relato de experiência do ensino da produção de objetos virtuais de aprendizagemThe development of teaching material for distance education, from theory to practice: an account of the experience of teaching the production of virtual learning objects