I need to access a “native” C library from Java via Java Native Access (JNA). The idiomatic way to do this seems to be defining an interface that extends Library and that declares all the functions which I need to access. Then create a singleton instance, via Native.load() method:

public interface MyLibrary extends Library {
    MyLibrary INSTANCE = Native.load("mylib", MyLibrary.class);
    int some_function(int param);
}

This works fine with functions. But how do I access global variables via the JNA interface?

In the C header file it is defined like:

extern const uint16_t SOME_GLOBAL_VARIABLE;

There is little to no information available on how to access global variables via the JNA interface. The closest thing I have found is the NativeLibrary.getGlobalVariableAddress() method. But, unfortunately, this method is in NativeLibrary class, not in the Library interface!

And there also seems to be no way to get a NativeLibrary instance when working with a custom interface (derived from the Library interface) and with the Native.load() method. I probably could use NativeLibrary.loadLibrary() instead, in order to get a NativeLibrary instance and be able to use getGlobalVariableAddress(), but then, how do I apply my interface to that in order to invoke the functions? In other words, is there any way in JNA to go from Library to NativeLibrary or vice versa?