Hello Mohammad,
Well,in my opinion just go through the constructors of classes in io Package and if possible also try to remember hierarchy. The best source for that is API.
In my time I am also weak in IO. Then, I tried in this manner and by GOD's grace I got 100% in IO.

I wish you too can do it.

Gurpreet Sachdeva
For Mock Exams FAQ and some useful information about Bitshift operator, inner classes, garbage collection,etc please visit:
http://www.go4java.20m.com
Regards<BR>Gurpreet Sachdeva<P>For Mock Exams, FAQ, Exam tips and some useful information about Bitshift operator, inner classes, garbage collection,etc please visit: <A HREF="http://www.go4java.lookscool.com" TARGET=_blank rel="nofollow">http://www.go4java.lookscool.com</A>