[ale] OT: Java jar files

[Kevin Krumwiede]

The classpath is probably one of the most confusing things about Java.
Basically, it is a list of roots where the JVM will look for package trees.
You don't need /usr/java/jdk1.3.1_01 in your classpath unless that's where
you're storing all your non-standard classes (and I wouldn't, because they
don't belong to JDK 1.3.1.)  To illustrate, if your classpath is
"/usr/java:$HOME/java:." and your program uses "yourpackage.YourClass", the
JVM will attempt to load "/usr/java/yourpackage/YourClass.class", then
"$HOME/java/yourpackage/YourClass.class", and finally
"./yourpackage/YourClass.class".  The JVM will always find its standard
library classes, regardless of whether they are on the classpath.

Anyhow, to get Java to use a jar file as one of its classpath roots, that
jar file must be specified by name in the classpath (e.g.,
CLASSPATH="$CLASSPATH:crimson.jar") both when you compile the program and
when you run it.

Fortunately, java and javac both take a -classpath (or -cp) argument on the
command line, so you can leave your default classpath set to something
general.  Note that the command-line classpath is used instead of (not in
addition to) the environment classpath, so you may have to use '-cp
"$CLASSPATH:jarfile.jar"'.

Krum


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