When I was a student I did all projects in Java/Eclipse. But my first job was to maintain ASP.NET C# web app, so I switched to VS. Last year I had to build a small Andorid app for a friend of mine, it went well, and this year I'm developing Windows Phone app.

The point is, learn OOP basics well, focus on things written in the book called Code Complete or something similar, and look at the big picture. Most of the time your apps will have server and client side, and most of the time you will have to develop server side that will be suitable for any client platform there is. For example, I code best in C#, so I use C# to code server side as RESTFul Service, that can be used by both Andorid or WP apps easily.

And at the very end, I would recommend you to learn C# and XAML (WPF, Silverlight), because you can use it for programming apps for both WP and Windows OS, which still has a big portion of the market when it comes to devices overall.

PS. Sorry for mistakes, I'm not a native English speaker