Ultimately, the best advice would be to learn both c# and java.

And why not? Both languages are very similiar.

I have and this is just a hobby for me after school hours.

well i already know both languages, it's not a big deal that if you know either of these (c# or java) then you can easily learn the other.

But the problem lies in profession, where people look for your expertise and evaluate them from the project you have done in the recent past while you were in the company. If i had done a few projects in Java then where ever i'll send my CV they will consider me for Java not for .NET (C#).

I know sticking to a technology is not a good idea. In Computer Science, technolgy changes in hours. The goal to success is to be logical and conceptual. But these things sometimes not evaluated by the companies which are expected to hire us. They look for the recent experience and go for job only related to that experience and we miss sometimes a big chance.