Java is an object oriented language which places emphasis on code
reuse. It is typical to reuse code previously developed and make it
available within current project. Even Standard edition consists of
about 3000 classes providing basic functionality and practices.
Managing this Zoo as individual classes would be cumbersome.
You can reuse the classes previously developed either by:
- listing directories which contain classes in
the CLASSPATH.
- incorporating classes in the jar file, and
adding jar to
the CLASSPATH.
The
jar file stands for
Java
ARchive. The utility
to process these files is called
jar. It uses similar
syntax as popular UNIX
tar utility. Format of the
jar is that of
zip file rather
than
tar file, and these files can be created/unpacked
also with the popular
zip/unzip utility,
i.e.:
unzip some.jar
and
jar xvf some.jar
do the same thing: unpack the archive.