Packages - The Java Language Specification - page 161

A package may not contain two members of the same name, or a compile-time error results.
Here are some examples:
• Because the package java.awt has a subpackage image , it cannot (and does not)
contain a declaration of a class or interface type named image .
• If there is a package named mouse and a member type Button in that package
(which then might be referred to as mouse.Button ), then there cannot be any
package with the fully qualified name mouse.Button or mouse.Button.Click .
• If com.nighthacks.java.jag is the fully qualified name of a type, then there can-
not be any package whose fully qualified name is either com.nighthacks.java.jag
or com.nighthacks.java.jag.scrabble .
It is however possible for members of different packages to have the same simple
name. For example, it is possible to declare a package:
Click here to view code image
package vector;
public class Vector { Object[] vec; }
that has as a member a public class named Vector , even though the package java.util also
declares a class named Vector . These two class types are different, reflected by the fact
that they have different fully qualified names (§ 6.7 ) . The fully qualified name of this
example Vector is vector.Vector , whereas java.util.Vector is the fully qualified name of the
Vector class included in the Java SE platform. Because the package vector contains a
class named Vector , it cannot also have a subpackage named Vector .
The hierarchical naming structure for packages is intended to be convenient for organizing
related packages in a conventional manner, but has no significance in itself other than the
prohibition against a package having a subpackage with the same simple name as a top
level type (§ 7.6 ) declared in that package.
For example, there is no special access relationship between a package named oliver
and another package named oliver.twist , or between packages named evelyn.wood and
evelyn.waugh . That is, the code in a package named oliver.twist has no better access to
the types declared within package oliver than code in any other package.
7.2. Host Support for Packages
Each host system determines how packages and compilation units are created and stored.