I still don't understand most of the classes in the java API but can easily understand the other methods of classes that I already know. Ex. Math class has pow(int x, int y) method which i already know from tutorials. I needed a method to determine which among two integers in bigger. Upon reading more of the methods in the Math class, I saw max() which does this.
Personally, a good book and javaranch will help a lot.
You can certainly read books to get you started with the basic APIs, but for anything beyond the basics, there's really no substitute for experience. When in the course of a real programming project you need to use an API you haven't used before, have a look at it, read a tutorial or book about it if necessary, but then simply use it. Experience is the best teacher.
When I first learnt of the existence of and looked at the API , I went EEK!Gosh ,It`s massive,Which of course it is.I am just a beginner at java in the true sense - coming on for six months in the hot seat now.My recipe for learning the object methods within the API is to write a class which (if possible) contains all the methods for that particular object call.It`s maybe stating the obvious(if it is I appologise)but writing code does help to remember and you are learning to construct classes at your particular level at the same time.
an island in the sun <br />with a language of many tongue?
First, you should learn how to navigate the API docs. These are a great resource, especially when you already have a good idea what class or package you need to look at. It's impossible to memorize every single set of parameters and return values for all the methods available, let alone which method belongs to which class.
Second, you should take a look at Sun's Java Tutorial. This is a great place to at least get your feet wet with the basics of different parts of the API.
Third, as someone already mentioned, experience will take you a long way. I mostly say this because I feel like I lack "real world" experience. All my knowledge about programming in general and Java specifically is rather academic.
Another great way to explore the API and other cool features is to subscribe to Sun's Core technology and Language Fundamentals Newsletters. I think they are weekly. They include short/simple examples and echniques for common problems and some not so commonly used but useful classes/packages of the API. The link is http://developer.java.sun.com/subscription/
I guess you will need some beginners guide on Java. Learn how to navigate through the api first. As you ride further with this bandwagon, the web and some java forums will be your "companion guide". APIs are just references remind you of class methods and etc; it is the methodologies that you need to pick up.