Non-public top-level class vs static nested class

Question

It seems to me that non-public top-level classes and static nested classes essentially perform the same tasks when creating a helper class.

A.java

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Answer 1

In neither example do you have one class per source file. But generally, you use a static nested class to signify that it is only intended to be used within its enclosing class (forcing it to be referenced as A.AHelper). That is not so clear if you move that class to the top level.

From the Sun tutorial:

Logical grouping of classes—If a class is useful to only one other class, then it is logical to embed it in that class and keep the two together. Nesting such "helper classes" makes their package more streamlined.