Which Java API's must a Expert Java Developer know thoroughly ?

Question

There are more than 3000 classes in Java how can Java Developer remember or be aware of most
of them if he wants to become a Core Java Expert. Concepts like Object Orientation, Java Programming Syntax, Operators, Flow Control, Exceptions,
Assertions, String Formatting/Parsing, Collections and Generics, Inner Classes, Threading should be
basic and needs to be known by all Java Programmers.
But when it comes to remembering / awareness about 3000 or so Java classes how can a Java Developer
know all of them. As on job its not possible that one will come in touch with all of Java's classes
its only a limited section that generally one works depening on his domain.
Please share list of packages that are important or one should be aware of ?
What must be the approach/methodology/process to remember these Java API's ?

Answer 1

java.lang.Swapnil wrote:
Please share list of packages that are important or one should be aware of ?It's more important you know how to quickly work out how to use a class, by perhaps reading the javadocs, or, more often, simply from the name of it, and the methods it provides. That's a knack you get from experience and practice. The other side of that coin is to be able to write classes and methods such that other developers can get using them quickly, by looking at the names.
What must be the approach/methodology/process to remember these Java API's ?Use them a lot. There's no other way.