How to convert a jar into so file and use it ?

Hello,

I have a very simple java test code that uses a public method called
'coucou' of a external jar called 'Hello.jar' which contains the
package 'hello' and the public class 'Hello'. Here is the test code
Tool.java:

import hello.Hello;

public class Tool
{
   public static void main(String[] args)
   {
     System.out.println("main program running");
     Hello.coucou();
   }
}

which I would usually compile, with the following commands:

$ gcj -O0 -g0  -C Tool.java --classpath=./:extern/Hello.jar
$ gij -cp .:extern/Hello.jar Tool

Now if I want to compile Tool.java natively with gcj, what do I need to do ?

I can create the shared library from the jar like this:
$ gcj -O0 -g0  -shared -findirect-dispatch -fjni -fPIC
extern/Hello.jar -o extern/Hello.jar.so


I can then compile Tool.java into Tool.o with:
$ gcj -O0 -g0  --classpath=./:extern/Hello.jar  -c Tool.java -o Tool.o

(altough this is using the jar and not the so ??)

But then, I'm stuck with creating the final executable, i.e. Tool.out

Any clues ?

Cheers
David