Java Cookbook, 4th Edition

Chapter 15. Packages and Packaging

15.0 Introduction

One of the better aspects of the Java language is that it has defined a very clear packaging mechanism for categorizing and managing its large API. Contrast this with most other languages, where symbols may be found in the C library itself or in any of dozens of other libraries, with no clearly defined naming conventions.¹ APIs consist of one or more package, packages consist of classes, and classes consist of methods and fields. Anybody can create a package, with one important restriction: you or I cannot create a package whose name begins with the four letters java. Packages named java. or javax. are reserved for use by Oracle’s Java developers, under the management of the Java Community Process (JCP). When Java was new, there were about a dozen packages in a structure that is very much still with us, though it has quadrupled in size; some of these packages are shown in Table 15-1.

Table 15-1. Java packages basic structure

Name	Function
java.awt	Graphical user interface
java.io	Reading and writing
java.lang	Intrinsic classes (String, etc.)
java.lang.annotation	Library support for annotation processing
java.math	Math library
java.net	Networking (sockets)
java.nio	“New” I/O (not new anymore): channel-based I/O
java.sql	Java database connectivity
java.text	Handling and formatting/parsing dates, numbers, messages
java.time	Java 8: modern date/time API (JSR-311)
java.util	Utilities (collections, date) ...