Nowadays, development is very eased from community.
We can easily re-use our code between different platforms in so many ways, gaining time, money and above all... today have multiple skills is not so as useful as before.
By the way, I recently had necessity to bring some java code to .NET runtimes.
No difficulties with IKVM.NET !
If you follow these steps you can convert from JAR to DLL or even from Runnable JAR to EXE!