CORBA - JavaTech: An Introduction to Scientific and Technical Computing with Java - page 535

and can be read but not set by a client. Regular attributes may be set by a client
using the mutator method.
Constants defined within a module but outside an interface in the IDL file
map into a public Java interface (with the same name as the constant) in the
package corresponding to the module in which the constant is defined. Thus our
COR19 - CONSTANT ,which is in the cor19 module, maps to a Java interface (in a
file named COR19 - CONSTANT.java )inthe javatech.cor19 package, while
the SERVER - CONSTANT , being in the server module, maps to a Java interface
in the javatech.cor19.server package. These Java interfaces define no
methods, just constant values in a field named value .Sothe constant can be
accessed like this:
String a - fun - chapter = javatech.cor19.COR19 - CONSTANT.value;
or, using imports,
import javatech.cor19.*;
...
String a - fun - chapter = COR19 - CONSTANT.value;
Constants defined inside an IDL interface map to public static final fields in the
Java interface that corresponds to the IDL interface.
There are more features to IDL that we do not go into here since our aim is only
to introduce CORBA rather than give an exhaustive tutorial. Some features that
might be of interest include the oneway keyword, which defines a non-blocking
method, the typedef keyword, enum and union objects, and the Any type.
19.3 Compiling the IDL file
The IDL-to-Java compiler provided with the Java 2 SDK is known as idlj .
There exist CORBA implementations for Java other than the free built-in imple-
mentation. Some of these may provide better performance or adherence to newer
versions of the CORBA standard than the built-in CORBA support. Each imple-
mentation must provide its own IDL compiler, and the name and usage of the
compiler is likely to be different from the name and usage of idlj .However,
most implementations should produce essentially similar output files, with per-
haps slight naming differences. We deal only with the free Java 2 SDK CORBA
implementation.
When the above IDL file, with its nested module statements, is compiled,
it generates the support classes in the javatech.cor19.server package.
The IDL file itself may be kept almost anywhere. We use a directory structure
similar to that used in the RMI example in Chapter 18 with an src directory
containing all the implementation files in a package-named directory structure
and a build/classes directory containing the compiled class files. With this
structure, it is convenient to keep the IDL file in the src directory. The IDL