kontai i use my jni functions from freepscal is the same the problem and i don't see my exported functions from delphixe5 i use idaq to decompile .so libs and look the import/export functions
and the big problem from sdl is that you don't have access to Java i think.
jni is global system form compilers like delphi/c++ create native code to java jni is just the headers to communicate java/native on android or windows .


""
procedure Java_org_libsdl_app_SDLActivity_onNativeAccel(
env:JNIEnv; cls:jclass;
x:jfloat;y:jfloat; z:jfloat);stdcall;""

Java_org_libsdl_app_SDLActivity
org.libsdl.app is the package name
onNativeAccel the name of the function imported from java exported from delphi
SDLActivity is the name of the activity

now on java
"
public static native void nativeInit();/declare function

class SDLMain implements Runnable {
@Override
public void run() {
// Runs SDL_main()
SDLActivity.nativeInit();

Log.v("SDL", "SDL thread terminated");
}
}


"