Packages - Multimedia Introduction to Programming Using Java - page 326

On Windows 95, you can use a set statement e.g.:

set CLASSPATH=C:\Gries\prog\vc;C:\jdk\;

In Unix systems
In a Unix system, how you look at and change CLASSPATH depends on which
“shell” you are using, so we give only a brief discussion here. Statement set or
setenv may be used to store a value in CLASSPATH . In this example:

set CLASSPATH=/usr/Gries/prog/vc:/usr/jdk/lib
the colon is used to separate paths and a slash is used to separate directory names.
But do not set CLASSPATH until you know what is already in it —you may want
to add paths to it, not just store a new set of paths in it.
To look at the contents of CLASSPATH , try statement set without arguments.
Also, look in files like .login and .cshrc for statements that set CLASSPATH .

11.3 The packages that come with Java

An implementation of Java comes with over forty packages, some of which con-
tain subpackages. We mention the more important ones.

Package java.lang The most important package (“ lang ” stands for “lan-
guage”). It is automatically imported, so you do not need an import statement for
it. It extends the core language with several classes that you will use often. Here
are the more important classes.
Class Object is the root of the hierarchy of classes. Every other class has
Object as a superclass, so its methods are inherited by all classes. See Sec. 4.3.1.
Classes String and StringBuffer provide implementations of sequences
of characters. See Sec. 5.2.
The eight wrapper classes, including Integer and Character , provide
instances that contain the values of primitive types. Class Void is used to repre-
sent the primitive Java type void . See Sec. 5.1.
Class Math contains useful methods, like abs , sin , and max . See Sec 1.1.7.
Class Class has methods that provide information about an object. For
example, get the name of the class of object obj using obj.getClass.getName .
Classes Throwable , Error , Exception , and RuntimeException are
involved with exception handling. See Chap. 10.

Package java.applet Provides the basic class, Applet , for implementing Java
programs that run on the world wide web. See Chap. 16.

Package java.awt Contains the classes of the “Abstract Window Toolkit”, which
is used to build GUIs. Some of these classes have been superceded by the Swing
classes —see package javax.swing , below.
Package java.io Contains the classes that help you do input-ouput, or IO. For