Enthuware

In addition, the programmer can define one top-level class as a static member of another top-level class. Unlike an inner class, a top-level class cannot directly use the instance variables of any other class. The ability to nest classes in this way allows any top-level class to provide a package-like organization for a logically related group of secondary top-level classes.

Inner classes and nested top-level classes are implemented by the compiler, and do not require any changes to the Java Virtual Machine. They do not break source or binary compatibility with existing Java programs.

A nested class is any class whose declaration occurs within the body of another class or interface. A top level class is a class that is not a nested class. An inner class is a nested class that is not explicitly or implicitly declared static. A class defined inside an interface is implicitly static.