which technology has demand in market java or .net?

There is a huge demand for both and I think it will even rise in upcoming years. So it is really up to you. I would go with .net, because I'm a .net biased freak ;)

This is not kind of a discrimination to be made. They are best on their areas. You can choose anyone of them, but before that judge yourself on which technology you can get a grip. There is always a bright future even in c, depends on the quality of expertise you have in that area.
I hope you understand.
Thanks