Two hotcakes in the market today in software industry are Java and .NET. Both of them use object oriented concepts heavily. So, I think the bestway to master an object oriented programming language is by mastering the concepts of Object orientation.
I am now reading a book called “Beginning C# Objects” by Jacquie Barker and Grant Palmer – Apress. Since I will be concentrating on C#, I choose a book which gives me introduction to Object Oriented concepts with examples in C#.
So, I think I have taken a health first step towards mastering .NET. You can find the basic and advanced concpents about OOPs in this section.