Java API Packages

As we have seen, Java contains many predefined classes that are grouped into categories of related classes called packages. Together, we refer to these packages as the Java Application Programming Interface (Java API), or the Java class library.

Throughout the text, import declarations specify the classes required to compile a Java program. For example, a program includes the declaration

 import java.util.Scanner;

to specify that the program uses class Scanner from the java.util package. This allows programmers to use the simple class name Scanner, rather than the fully qualified class name java.util.Scanner, in the code. A great strength of Java is the large number of classes in the packages of the Java API. Some key Java API packages are described in Fig. 6.6, which represents only a small portion of the reusable components in the Java API. When learning Java, spend a portion of your time browsing the packages and classes in the Java API documentation (java.sun.com/j2se/5.0/docs/api/index.html).

Figure 6.6. Java API packages (a subset).

Package	Description
java.applet	The Java Applet Package contains a class and several interfaces required to create Java appletsprograms that execute in Web browsers. (Applets are discussed in Chapter 20, Introduction to Java Applets; interfaces are discussed in Chapter 10, Object-Oriented Programming: Polymorphism.)
java.awt	The Java Abstract Window Toolkit Package contains the classes and interfaces required to create and manipulate GUIs in Java 1.0 and 1.1. In current versions of Java, the Swing GUI components of the javax.swing packages are often used instead. (Some elements of the java.awt package are discussed in Chapter 11, GUI Components: Part 1, Chapter 12, Graphics and Java2D, and Chapter 22, GUI Components: Part 2.)
java.awt.event	The Java Abstract Window Toolkit Event Package contains classes and interfaces that enable event handling for GUI components in both the java.awt and javax.swing packages. (You will learn more about this package in Chapter 11, GUI Components: Part 1 and Chapter 22, GUI Components: Part 2.)
java.io	The Java Input/Output Package contains classes and interfaces that enable programs to input and output data. (You will learn more about this package in Chapter 14, Files and Streams.)
java.lang	The Java Language Package contains classes and interfaces (discussed throughout this text) that are required by many Java programs. This package is imported by the compiler into all programs, so the programmer does not need to do so.
java.net	The Java Networking Package contains classes and interfaces that enable programs to communicate via computer networks like the Internet. (You will learn more about this in Chapter 24, Networking.)
java.text	The Java Text Package contains classes and interfaces that enable programs to manipulate numbers, dates, characters and strings. The package provides internationalization capabilities that enable a program to be customized to a specific locale (e.g., a program may display strings in different languages, based on the user's country).
java.util	The Java Utilities Package contains utility classes and interfaces that enable such actions as date and time manipulations, random-number processing (class Random), the storing and processing of large amounts of data and the breaking of strings into smaller pieces called tokens (class StringTokenizer). (You will learn more about the features of this package in Chapter 19, Collections.)
javax.swing	The Java Swing GUI Components Package contains classes and interfaces for Java's Swing GUI components that provide support for portable GUIs. (You will learn more about this package in Chapter 11, GUI Components: Part 1 and Chapter 22, GUI Components: Part 2.)
javax.swing.event	The Java Swing Event Package contains classes and interfaces that enable event handling (e.g., responding to button clicks) for GUI components in package javax.swing. (You will learn more about this package in Chapter 11, GUI Components: Part 1 and Chapter 22, GUI Components: Part 2.)

The set of packages available in the J2SE Development Kit (JDK) is quite large. In addition to the packages summarized in Fig. 6.6, the JDK includes packages for complex graphics, advanced graphical user interfaces, printing, advanced networking, security, database processing, multimedia, accessibility (for people with disabilities) and many other capabilities. For an overview of the packages in the JDK 5.0, visit

java.sun.com/j2se/5.0/docs/api/overview-summary.html

Many other packages are also available for download at java.sun.com.

You can locate additional information about a predefined Java class's methods in the Java API documentation at java.sun.com/j2se/5.0/docs/api/index.html. When you visit this site, click the Index link to see an alphabetical listing of all the classes and methods in the Java API. Locate the class name and click its link to see the online description of the class. Click the METHOD link to see a table of the class's methods. Each static method will be listed with the word "static" preceding the method's return type. For a more detailed overview of navigating the Java API documentation, see Appendix G, Using the Java API Documentation.

Good Programming Practice 6.2

The online Java API documentation is easy to search and provides many details about each class. As you learn a class in this book, you should get in the habit of looking at the class in the online documentation for additional information.