Though I am a Bachelor of engineering(BE) from India,I think I can answer your question
"And what does an MCA do?"
MCA students are supposed to have good analytical and reasoning skills with a strong knowledge of a programming language...generally C,C++ or Java.
Software Companies in India like to recruit MCA candidates after the necessary interview rounds.
Hope this answers your question.
An MCA student will focus not just on Java but 100% committed to go rigorous training in learning data bases, System analysis & design (SAD), data modeling, OOPS, Student desired Computer Programming Languages & design aspects(VB, C, .net, Java etc), Operating systems (UNIX, Windows), Networking , Security.
Part of their course they are also strongly been advised to work in Real time environment for their Project work (typically 3 to 6 months).
Hope this helps for better understanding of what is MCA can do