The Java® Language Specification, Java SE 7 Edition, Fourth Edition

7.4. Package Declarations

A package declaration appears within a compilation unit to indicate the package to which the compilation unit belongs.

7.4.1. Named Packages

A package declaration in a compilation unit specifies the name (§6.2) of the package to which the compilation unit belongs.

PackageDeclaration:    Annotations_opt package PackageName ;

The package name mentioned in a package declaration must be the fully qualified name (§6.7) of the package.

The PackageName in a package declaration ensures there is an observable package with the supplied canonical name, and that it is not subject to the rules in §6.5.3 for determining the meaning of a package name.

The scope and shadowing of a package declaration is specified in §6.3 and §6.4.