error starting java .jar app - classpath issue?

[Gordon Pedersen <gordon@visi.com>]

I'm reluctant to post to a developers list, but this question
got no help at debian-user in the past 2 days.  It seems to be
debian-related more than generic java-related.

This is likely a very simple issue.  I've never tried to run a
java .jar library on debian before.

For all commands discussed below, no CLASSPATH environment 
variable has been defined.

No errors if I switch to the .jar file directory and issue this
command:

        $ java -jar tt.jar

But if if try either of the following commands from another
directory, the errors shown below commands appear:

        $ java -jar /usr/share/java/tt.jar
        $ java -classpath /usr/share/java/tt.jar -jar /usr/share/java/tt.jar

Exception in thread "main" java.lang.NullPointerException
        at javax.swing.ImageIcon.<init>(ImageIcon.java:161)
        at com.taubler.timebox.submit.SubmitExtensionWidget.<init>(SubmitExtensionWidget.java:16)
        at com.taubler.timebox.submit.SubmitManager.<init>(SubmitManager.java:52)
        at com.taubler.timebox.TimeTracker.<init>(TimeTracker.java:54)
        at com.taubler.timebox.TimeTracker.main(TimeTracker.java:1115)

I wonder if it may just be a matter of learning how to correctly
set the CLASSPATH before issuing the java command on .jar
libraries held in /usr/share/java/.  I could not find any
clear guidance about the usual CLASSPATH practice on debian.

(I run sarge.  Java is from blackdown j2re1.4 and j2sdk1.4.
Installed without a hitch.)

(App in question is a timekeeper program.  See
http://www.taubler.com/timebox/.)

Thanks.


-- 
Gordon Pedersen             gordon@visi.com
St Paul,  Minnesota,   USA