Dear Zahid
In my opinion, first you go through the objectives of exam available at sun's site and after getting command and clear your concept
you should to appear in the mocks exams available here in javaranch or the other places at net. They will really give you the idea to assess yourself.
I think for the
scjp preparation there is no need to stuck in the large applications or large code. Just try to clear your concept by writing small code in difference ways and senarios.
As far as my knowledge is concern the exam doesn't contain large code more than 30 lines. I think there may be a very few questions upto these lines in their codes otherewise sun just check your knowledge and the command on their objectives which they have clearly specified on their site.
Hope this little suffice your querry.
Wish you a best luck for the exam ! I am also working on it
~Rashid