Fully qualified class name consist of package name and class name. As in my previous post "com.my.package" is package name and "Main" is the class name.
Package translates 1:1 to the folder structure, so for the given package "com.my.package" the folder structure would be like this
In Your example, You are not using package so Your fully qualified class name is the same as the simple form "Main"http://en.wikipedia.org/wiki/Fully_qualified_name
Why package names ? It's a form of namespace. Imagine using 7 different libraries, non using packages and everyone having a "Main" class. How would You tell Your program, which one to use ?
That's why there are packages. All libraries and programs in java world are in packages. There are also other benefitshttp://docs.oracle.com/javase/tutorial/java/package/index.html