The classpath of runGuiDemo.bat is set by java -cp %my_classpath%, but it needs quotes around it like java -cp "%my_classpath%" in order to not throw a very confusing error when the classpath contains spaces:

Exception in thread "main" java.lang.NoClassDefFoundError: and
Caused by: java.lang.ClassNotFoundException: and
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
Could not find the main class: and. Program will exit.