Hi Nidhi,
I'll give you some ideas, AND I'd like to hear what ranchers who have taken the exam think...
First off, you don't need to memorize ALL of the methods in the classes you're studying. Only the most commonly used ones. So that brings up the question, how do you know which are the most commonly used? Well the surest way is to get a book for the exam. Most of the authors have tried to focus on just the methods you'll need to know. The next idea is to ask here, and finally, part of the reason that the APIs are on the exam at all is so that candidates such as yourself will get used to using them. So, my guess is that if you looked at a given class, and used your common sense, you could probably do a pretty good job of determining which of the methods the exam creation team thought would be the most commonly used.
Another way of thinking about this is to understand what the exam creators had in mind with the APIs. Their goal was for candidates to be familiar with the basic capabilities of the most common classes. They really aren't trying to make this a trivial competition, they tried to get you to learn the stuff that they think you'll use over and over again in real life.
Now, it's true that the exam includes a few APIs that you won't use a lot, and there are some reasons for those exceptions, but in general, if you understand the most common reasons to use the classes listed, and you understand the most common methods you'll use in those classes, you'll do well on those portions of the exam.
I'll give you one example:
You should know that 'put()' is for Maps, and so it has two arguments. Similarly, you should know that 'add()' is for Lists and Sets, and so it has one argument.
hth,
Bert