The Java Base System Libraries and Utility Classes (Tutorial Page 14)
Java.lang: A collection of base types (language types) that are always imported into any given compilation unit.
Java.io: Streams and random access files classes. This where you find equivalents of stdio.h/standard lib from Unix.
Java.net: Provides support for sockets, telnet interfaces, ftp and URLs
Java.util: Container and utility classes such as dictionary, tables, stacks, and date/time
Java.awt: An Abstract Windowing Toolkit that provides an abstract layer enabling you to port Java applications easily from one window system to another. Library contains classes for basic interface components such as events, colors, fonts and controls such as buttons and scrollbars
