Notepad class should be public

After all these years I never noticed that the Notepad.java is not a public
class and it is package private. The problem is that java launcher uses
jni and it really does not care whether the class is public or proteced,
and the main class can be be invoked.

This is not the case with java.reflect.Method.invoke, it expects that
class to be public. This is not a problem with the other demos.