It is possible, but you'll need to do some work to get them calling properly. I've never done it myself, but until someone better equipped to answer the question comes along here's a few places to start.
Take a look at the JNI (Java Native Interface, google or wikipedia can tell you more), which lets you call out from Java to other languages. There seems to be a project called jni4net ( http://jni4net.sourceforge.net ) which is intended to do exactly what you want, but it's in alpha at the moment and might not be stable enough. Still it could be worth having a look.
You can also do it yourself, calling through the JNI as a C call which will then get through to the CLR eventually, but it looks like a lot of effort. I know this isn't a quick and easy solution, but it might give you a couple of places to get started. also http://www.codeproject.com/KB/cross-platform/javacsharp.aspx seemed to be a fairly good look at how to go about it.
As all of the other answers so far have said though, it's fiddly and a pain. If you can do something else instead, it will probably be worth it.
Have a look at Jni4Net and this stack overflow question: is there an effective tool to convert c# to java?
You would have to use native calls which would a) be really irritating to keep up to date and B) defeat the huge advantage of java being cross-platform.
Your best bet might be to try to find something that can convert C# to java--or better yet recode your C# code into java.
In the long run it will save you a lot of stress.
Diferent compilers dud, it's not possible. Unless You use java sharp language in visual studio, then the compilers mach.
