Need some suggestions on ABAP webdynpro ..

Hi

I am actually a java guy. But now i m moving to Object Oriented ABAP. I have to work in ABAP Webdynpro. Could anyone please tell me

How much time it will take to learn OOAbap ?

Could u please suggest me which book is best for learning OOABAP ?

Any online books are available?

Thanks & Regards

Ravi Shankar B