whats the diffrence between java and C#
Unity uses Javascript or C# as scripting languages.
Java is a totally independent language that has no place in Unity.
They both provide the same functionality set when it comes to scripting with Unity, but their syntax differs. It is totally up to you which one to use. Although it seems many beginners prefer JavaScript, I tend to prefer C#.
C# is part of the .NET framework and is platform dependant.
Java included with the interpreter on the target platform ( Any ) can be used everywhere.
Both languages use OOP (Object Orinted Programming) in the mainstream programming scene.
C# Has some cost/gain questions on mostly Object cleanup and collections, and everything is passed as a reference by default whilst Java is sometimes considered an underachiever on performance benchmarks (Troll what you want on this comment but make it usefull for this topic!).
I don't really know that much about either but I would STRONGLY suggest that you think about what you want to know. Learning both languages isn't something you should casually throw on your TO-DO list.
Do you want to have a specific task application function or purpose in mind? A project mabye?
What is that project supposed to do , who uses it , how much time and effort can I invest in this (learning new languages can be a long road).
When you have a target/goal you can start looking up on what you need from C# or Java , and in the case of Unity3D Javascript. Make sure the engine you want supports your needs!!! It is really a "BAD DAY" to find out later you can't use something you built!!!
Now that you have a goal and something to build it in start thinking about language perks. I want a heavy graphical game? In XNA? Well that would mean a .NET language, in unity3D Javascript or plugins. You want performance and control and microoptimize a GPU for a company application that needs to improve? Consider C++ or C. You want a small APP and not invest to much time in learning curve while you have C# experience? Try Java.
Short:
1) What is my goal?
2) What engine is going to help me , or framework, platform, what are you depending on?
3) What languages can I use to accomadate step one and respect step 2
Selecting language: Google + Community/Developer views on building a similar project in your language. Listen carefully to what happened in programming world because there's a lot of user experience out there so you don't have to make their mistakes.
Try this: http://tinyurl.com/625cy3v
I assume you meant JavaScript (UnityScript) and not Java, people are picky about names here. There are a few differences between them which are listed in the language comparison on unifycommunitys wiki. It doesn't look complete but I guess it's one of the best resources available yet. You can start in either language and then try the other if you like. The languages are pretty similar, with only a few differences I've encountered so the transition is pretty easy.