collection of APIs(Application Programming Interface)
- java.lang automatically imported into Java programs
- java.util useful utility classes (有用的实用工具类) (e.g. Date)
- java.io Input/Output classes
- java.awt windowing classes (窗口类)
- javax.swing Java foundation classes (JFC/Swing)
- java.net networking classes
Java课笔记-API概述
原文：http://www.cnblogs.com/WJQ2017/p/7580970.html
