Rules for creating Java source files

■ There can be only one public class per source code file.
■ If there is a public class in a file, the name of the file must match the name
of the public class. For example, a class declared as public class Dog { }
must be in a source code file named Dog.java.
■ If the class is part of a package, the package statement must be the first line
in the source code file, before any import statements that may be present.
■ If there are import statements, they must go between the package statement
(if there is one) and the class declaration. If there isn't a package statement,
then the import statement(s) must be the first line(s) in the source code file.
If there are no package or import statements, the class declaration must be
the first line in the source code file.
■ import and package statements apply to all classes within a source code file.
In other words, there's no way to declare multiple classes in a file and have
them in different packages, or use different imports.
■ A file can have more than one nonpublic class.
■ Files with no public classes can have a name that does not match any of the
classes in the file.