JSR 202 relaxes the prior restrictions on the legal characters
in a class name. If you use some newly legal characters in a
class name such as the SPACE character or other characters which
must be escaped in the URL the class may be found.

For example, an applet class named "Fo o" (with a space between
the two 'o' characters) and an http codebase will result in
appletviewer attempting to fetch a file named "Fo".

This problem is not specific to appletviewer but applies to all
classes loaded through a URLClassLoader include applications
classes loaded through the "system class loader".