By checking the Codename One website and ParparVM Github, its guide only show how to build the Java (with Java Main function entry point) into the native executable/app (iOS), but I can't find any guide to build/compile Java into iOS share library (either in C source or binary, as long as can be reused by swift/objective-C from iOS app).
So are we able to do so? is there any guide for that?
It wasn't designed for that purpose so it probably won't work well for it. There are some inherent design decisions that would make it very difficult to get ParparVM to work with a library. Two big ones:
The GC needs to work with roots and would have a hard time collecting without full control of the app
The code generated looks "awful". Method names translate to very long function names in C with a very convoluted syntax to allow all sort of VM edge cases such as covariance
I suggest you look at J2ObjC. I haven't checked it out in ages but it was designed exactly with this use case in mind. It doesn't have a "real" GC but that might be OK with ARC. It works with your sources and produces libraries that look a bit more "natural" on iOS.