The tutorials on the site contains both the source code (.java files)
and compiled code (.class files) in the jar file found in the lib
folder (lib\espresso3dtutorialN.jar). You can open the jar with your
favorite zip program.
The bat file is simply an easy way to launch the compiled program also
contained in the jar on Windows. On a Mac, you can write a similar
script to launch it or run it from the terminal/command line. If you
look at the contents of the bat file, you'll see the parameters to
launch it via Java and you can mimic this on the Mac.
Curt