PACKAGES

Compilation Units

7.3

In fact, the standard JavaSoft Java Developer's Kit on UNIX differs from the

very simple discipline described here only in that it provides a

CLASSPATH

 envi 

ronment variable that specifies a set of directories, each of which is treated like the

single directory described here. These directories are searched in order for defini 

tions of named packages and types.

A package name component or class name might contain a character that can 

not correctly appear in a host file system's ordinary directory name, such as a Uni 

code character on a system that allows only ASCII characters in file names. As a

convention, the character can be escaped by using, say, the

@

 character followed

by four hexadecimal digits giving the numeric value of the character, as in the

\uxxxx

 escape ( 3.3), so that the package name:

children.activities.crafts.papierM\u00e2ch\u00e9

which can also be written using full Unicode as:

children.activities.crafts.papierMache

might be mapped to the directory name:

children/activities/crafts/papierM@00e2ch@00e9

If the

@

 character is not a valid character in a file name for some given host file

system, then some other character that is not valid in a Java identifier could be

used instead.

7.2.2   Storing Packages in a Database

A host system may store packages and their compilation units and subpackages in

a database.

Java allows such a database to relax the restrictions ( 7.6) on compilation

units in file based implementations. For example, a system that uses a database to

store packages need not enforce a maximum of one

public

 class or interface per

compilation unit. Systems that use a database must, however, provide an option to

convert a Java program to a form that obeys the restrictions, for purposes of export

to file based implementations.

7.3   Compilation Units

CompilationUnit

is the goal symbol ( 2.1) for the syntactic grammar ( 2.3) of

Java programs. It is defined by the following productions:

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