Often you will want to regularly use some utility code that
you have developed or have obtained from a third party in your Java programs.
These may sometimes be set up as packages, just as the Java utilities are in
packages such as java.util.*
. Whether or not they are packages
or just a set of classes, you will want to store them in one place, separate
from the directory where you are developing your program.
Sometimes these libraries have a set of files stored in a single jar
file (which is a file using zip format
with a .jar
extension). In order to make this
work, the Java compiler and run programs must be able to find any of these.
This is done for command line use of Java and for some editors and IDEs
by setting an environment variable
called CLASSPATH. In Windows, the CLASSPATH environment variable should look
like the following:
Note the "."
at the end. This includes the
current directory in the search for classes.
Here we assume that we have a directory MyJavaLib
on the C-drive that contains some utility classes or the directories that
correspond to some packages. That is
the part before the first semi-colon. The
second part indicates that we have some classes stored in a file myutils.jar (these may just be classes or
may include a directory structure for packages – all that is within the jar
file). The third part indicates that
we have a jar file blackboxclasses.jar.
This is another jar file, in this case one very similar to one that might
be distributed with the Java Marine Biology Simulation Case Study.
Finally, after the last semi-colon we have the period, indicating that
the current directory is on the CLASSPATH. If
some things are stored in directories that are subdirectories, the complete
path, starting with "c:\"
should be in the CLASSPATH.
Open the autoexec.bat
file on the C-drive (c:\autoexec.bat) in an editor. Add the line
where the actual path is the one appropriate for your setup. Save and you are all set. You will probably have to reboot the machine or at least log off and log on before it takes effect. There is always a possibility on Win95 or Win98 that you will get an "out of environment space" message and the CLASSPATH will not be set. In this case, open a DOS window by selecting it from the start menu. Right click on the icon at the top left of the window and select properties. Select memory, and set the environment to the highest setting (4096). Then you should be fine.
Right click on the "My Computer" icon.
Select Properties. Select
Advanced. Click on Environment
variables. You probably want
this set for the system, although you can do it for the user.
For the system, select New and in the Variable Name field
type "CLASSPATH" and in the Variable Value window type the CLASSPATH
as it appears above. If you want to
modify an existing CLASSPATH, just select it and click Edit.