How to set classpath?

The command "env" will show all your current environment variables.
To set a variable in current session do:
CLASSPATH="/usr/local/whatever"
export CLASSPATH
To set classpath so that it is default for all bash sessions in the future, edit the file /etc/profile

Remember that it should be upper case like CLASSPATH, and not like classpath.

A little tip btw is to add a new path to your existing CLASSPATH. It can be done like this:
export CLASSPATH="$CLASSPATH:/usr/local/xerces-2_4_0/xercesImpl.jar:/usr/local/xerces-2_4_0/xmlParserAPIs.jar"

Finally you can also do "echo $CLASSPATH" to see what it is. Or "env | grep CLASSPATH"