How to find the documentation of any java library class or interface

Suppose we want to check this class
java.util.Array
There are two ways
1.If you have an Internet connection then just google
oracle java.util.Array
This gives you the latest documentation
2.If you do not have Internet due to any reason then go to the java folder
open JDK
there will be a compressed folder with name src
open it and then open java folder
then open util
then you can find Array named java source file just open it in a IDE and generate documentation