Statement package: that class in that position, and the only one on the first line package cn.day09;
Import package: a package and is not introduced under this category class, and can be more sentences can not appear in the first line of import java.util *;.
* Represents a wildcard match all packets in the current class
There are three main package
Java (Primal package)
lang package: When all content using the core libraries when the program starts automatically load the next package without lead pack
util Package: providing a number of tools and the operation of the class object (Arrays, Scanner ...)
applet, awt :( graphical interface)
io packet: Data transfer
math: provides a simple math
net: network data transmission
nio: high concurrency
security: detect security package
sql: Operation Database
text: Formatting
Time: We provide the date and time
the javax (Expansion Pack)
org (third-party vendors Apache)