7.7

Unique Package Names

PACKAGES

create a situation that is difficult or impossible for the user or programmer to

resolve. The class

ClassLoader

 ( 20.14) of the standard Java Virtual Machine

environment can be used to isolate packages with the same name from each other

in those cases where the packages will have constrained interactions, but not in a

way that is transparent to a naive Java program.

You form a unique package name by first having (or belonging to an organiza 

tion that has) an Internet domain name, such as

Sun.COM

. You then reverse this

name, component by component, to obtain, in this example,

COM.Sun

, and use this

as a prefix for your package names, using a convention developed within your

organization to further administer package names.

Such a convention might specify that certain directory name components be

division, department, project, machine, or login names. Some possible examples:

COM.Sun.sunsoft.DOE

COM.Sun.java.jag.scrabble

COM.Apple.quicktime.v2

EDU.cmu.cs.bovik.cheese

GOV.whitehouse.socks.mousefinder

The first component of a unique package name is always written in all uppercase

ASCII letters and should be one of the top level domain names, currently

COM

,

EDU

,

GOV

,

MIL

,

NET

,

ORG

, or one of the English two letter codes identifying coun 

tries as specified in ISO Standard 3166, 1981. For more information, refer to the

documents stored at

ftp://rs.internic.net/rfc

, for example,

rfc920.txt

and

rfc1032.txt

.

The name of a package is not meant to imply anything about where the pack 

age is stored within the Internet; for example, a package named

EDU.cmu.cs.bovik.cheese

 is not necessarily obtainable from Internet address

cmu.EDU

 or from

cs.cmu.EDU

 or from

bovik.cs.cmu.EDU

. The Java convention

for generating unique package names is merely a way to piggyback a package

naming convention on top of an existing, widely known unique name registry

instead of having to create a separate registry for Java package names.

If you need to get a new Internet domain name, you can get an application

form from

ftp://ftp.internic.net

 and submit the complete forms by E mail

to

domreg@internic.net

. To find out what the currently registered domain

names are, you can

telnet

 to

rs.internic.net

 and use the

whois

 facility.

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