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
Project
|_ src
|_ com
|_ my
|_package
|_ Main.java
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_nameWhy 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 benefits
http://docs.oracle.com/javase/tutorial/java/package/index.html