Real-world programs are neither monolithic nor static -- they are constructed
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 behavioural. 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 various 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
organisations 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 tracking
systems, and find that they are common