What Java Developers Know About Compatibility, And Why This Matters

Real-world programs are neither monolithic nor static – they are con-structed using platform and third party libraries, and both programs and libraries continuously evolve in response to change pressure. In case of the Java language, rules defined in the Java Language and Java Virtual Machine Specifications define when library evolution is safe. These rules distinguish between three types of compatibility- binary, source and be-havioural. We claim that some of these rules are counter intuitive and not well-understood by many developers. We present the results of a survey where we quizzed developers about their understanding of the var-ious types of compatibility. 414 developers responded to our survey. We find that while most programmers are familiar with the rules of source compatibility, they generally lack knowledge about the rules of binary and behavioural compatibility. This can be problematic when organisa-tions switch from integration builds to technologies that require dynamic linking, such as OSGi. We have assessed the gravity of the problem by studying how often linkage-related problems are referenced in issue track-ing systems, and find that they are common.