I created a classic hello world example with JNI and made a library, it has the visual studio project and some batch scripts since i was to lazy to manually do everything, lol. You might find it interesting!
http://www.mooload.com/new/file.php?file=/data/310507/1180615618/JNI+DLL.rarSome of the uses include
1.) People can't just *decompile* a dll, which means the source is safe :-)
2.) Fast execution time ( except loading the library )
3.) Allows you to use native code
4.) You reap the benefits of how a DLL works.
Disadvantages
1.) Only usable on Windows
2.) Some other shit i don't want to explain