Question

what are the perquisites for learning java. like one eager to learn calculus should have a little knowledge of algebra. what is it for learning java.

Answer 1

Java isn't particularly hard to learn.
As far as a first programming language, it's pretty ideal because of how popular it is - whatever problems you have, there will be answers available online.

As far as pre-requisites...Well, logical thinking and basic mathematics pretty much.
Nothing hugely complex.

Answer 2

Agreed about the lack of any real prerequisites, the local Coder Dojo is teaching Java to kids as young as 7. I'm not a big fan of the language, myself, but there are worse choices, I suppose.

If you can give a clear set of directions that any idiot can follow, you're in good shape.