PACKAGES

Unnamed Packages

7.4.2

If a type named

T

 is declared in a compilation unit of a package whose fully

qualified name is

P

, then the fully qualified name of the type is

P.T

; thus in the

example:

package wnj.points;

class Point { int x, y; }

the fully qualified name of class

Point

 is

wnj.points.Point

.

7.4.2   Unnamed Packages

A compilation unit that has no package declaration is part of an unnamed package.

As an example, the compilation unit:

class FirstCall {

public static void main(String[] args) {

System.out.println("Mr. Watson, come here. "

+ "I want you.");

}

}

defines a very simple compilation unit as part of an unnamed package.

A Java system must support at least one unnamed package; it may support

more than one unnamed package but is not required to do so. Which compilation

units are in each unnamed package is determined by the host system.

In Java systems that use a hierarchical file system for storing packages, one

typical strategy is to associate an unnamed package with each directory; only one

unnamed package is available at a time, namely the one that is associated with the

 current working directory.  The precise meaning of  current working directory 

depends on the host system.

Unnamed packages are provided by Java principally for convenience when

developing small or temporary applications or when just beginning development.

Caution must be taken when using unnamed packages. It is possible for a

compilation unit in a named package to import a type from an unnamed package,

but the compiled version of this compilation unit will likely then work only when

that particular unnamed package is  current.  For this reason, it is strongly recom 

mended that compilation units of named packages never import types from

unnamed packages. It is also recommended that any type declared in an unnamed

package not be declared

public

, to keep them from accidentally being imported

by a named package.

It is recommended that a Java system provide safeguards against unintended

consequences in situations where compilation units of named packages import

types from unnamed packages. One strategy is to provide a way to associate with

each named package at most one unnamed package, and then to detect and warn

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