source code file

[jose chiramal]

Why is it that there can be only one public class per source code file , whereas there can be more than one non public class.

Is there any reason ...

[Christophe Verré]

Filename = public class name. How are you going to name your file if there are more than one public class ?

[Darryl Burke]

More to the point: because the JLS says so.
http://java.sun.com/docs/books/jls/third_edition/html/packages.html#7.6

When packages are stored in a file system (§7.2.1), the host system may choose to enforce the restriction that it is a compile-time error if a type is not found in a file under a name composed of the type name plus an extension (such as .java or .jav) ...