Question

In a program I am using two external jar libraries.
There is a class in the external library X invoking a method m of a class in the library Y. The library X was compiled with version 1.0 of library Y. However, since I am using library Y for other purposes in my code, I preferred to use its last version (let’s say 5.0).
My problem is that when I execute the code, library X complains that the method m is not there anymore (throwing a NoSuchMethod error). However, the method is there.

The problem could be related to the fact that I am using a newer version of the library Y than the one that was present at compilation time ? (although backward compatible, with different bytecode?). If that is the case then I will be a bit puzzled since I thought that java method calls were expressed in byte code as symbolic references (e.g., method signatures), and not as direct references (e.g., offsets), but I could have misunderstood something.

Thanks for any clarification !

Answer 1

[…] I thought that java method calls were expressed in byte code as symbolic references (e.g., method signatures), and not as direct references (e.g., offsets) […]

You thought correctly; but it’s possible that the method in Y v5.0 has a different signature from the method in Y v1.0, even if they have the same name; for example, it might have a different number of arguments now, or different types of arguments, or it might have become static or non-static.