I am trying to learn about jar files.
I have an application in a folder, with a number of text and image
files (all in the one directory).

I created a jar file with all the files in that directory, and
successfully launched the program with

java -jar Project.jar

But....when I take all other files except the jar file out of that
folder, it won't run and I get an "uncaught exception fetching image"
error. I thought the point was that a jar file wrapped everything up
into itself, and so once that was created, you didn't need to worry
about other files and could just export that on its own as your
application.

What am I doing wrong here?