There should be some header files as well. You *include* the header
files in your (native) code, and *link* with the library files.

But in order to use the lib files with JNI, you must have a shared
library or DLL specifically made for use with Java that follows the
naming and linking rules of JNI. It will contain native declared
methods that belong to the Java classes in your project.

You cannot use an arbitrary library directly from Java, but you can
use its functions from a properly created JNI shared library.

To get started with JNI, read here:
http://java.sun.com/docs/books/jni/index.html
http://java.sun.com/javase/6/docs/technotes/guides/jni/index.html

/gordon