Class path entry could be jar, zip or directory (source)
set CLASSPATH=classpath1;classpath2...
Class paths to the .jar, .zip or .class files. Each classpath should end with a filename or directory depending on what you are setting the class path to:
For a .jar or .zip file that contains .class files, the class path ends with the name of the .zip or .jar file.
For .class files in an unnamed package, the class path ends with the directory that contains the .class files.
For .class files in a named package, the class path ends with the directory that contains the "root" package (the first package in the full package name).
Multiple path entries are separated by semi-colons. With the set command, it's important to omit spaces from around the equals sign (=).
The default class path is the current directory. Setting the CLASSPATH variable or using the -classpath command-line option overrides that default, so if you want to include the current directory in the search path, you must include "." in the new settings.
Classpath entries that are neither directories nor archives (.zip or .jar files) nor * are ignored.