A Study on Behavioral Backward Incompatibility Bugs in Java Software Libraries

Nowadays, due to the frequent technological innovationand market changes, software libraries are evolving veryquickly. To make sure that existing client software applicationsare not broken after a library update, backward compatibilityhas always been one of the most important requirements duringthe evolution of software platforms and libraries. However, due to various reasons, backward compatibility is seldom fullyachieved in practice, and many relevant software failures arereported. Therefore, it is important to understand the status, major reasons, and impact of backward incompatibilities in realworld software. Previous studies on this topic mainly focus onAPI signature changes between consecutive versions of softwarelibraries, but behavioral changes of APIs with untouched signaturesare actually more dangerous and are causing most realworldbugs because they cannot be easily detected. This paperpresents an empirical study on 126 real-world software bugreports on backward incompatibilities of software libraries. Wefind that 67% of fixed client bugs caused by backward incompatibilitiesin software libraries are fixed by client developers, through several simple change patterns made to the backwardincompatible API invocations.