can't run my jarmake output

[John Dalbey <jdalbey@calpoly.edu>]

JGNAT looks really neat so far ...

$ jgnatmake blastoff
jgnat -c blastoff.adb
jgnatbind -x blastoff.ali
jgnatlink blastoff.ali

$ java blastoff

Countdown to JGNAT ...
   10    9    8    7    6    5    4    3    2    1    0
BLASTOFF!


So my Ada code runs on the JVM ... Cool!

but I can't figure out how to run the .jar files produced by the jarmake
tool.

$ jarmake -oblastoff.jar blastoff.class

$ java -jar blastoff.jar
Failed to load Main-Class manifest attribute from
blastoff.jar

Isn't all that's necessary is to provide the -jar switch on the command
line? It is NOT an applet, so I don't use appletviewer. Am I missing
some basic concept here?

I couldn't find any reference to the word "manifest" in the user guide.
I'm stumped.

Thanks,
--jd