J and the metamodel

Overview

The metamodel defined for Objecteering/UML is accessible through the J language. J uses metaclasses, meta-associations, meta-roles and meta-attributes to navigate within a model and access model information.

J can also transform the metamodel, for example, change attribute values, create or determine model elements or modify links).

As we have already seen, J is used to define methods at metaclass level.

Handling rules

Figure 1. Part of the metamodel (simplified)

In Figure 1-1, the names of all the attributes whose visibility is "public" ("printPublicAttributes()" J method) can be displayed.

Class:printPublicAttributes()

{

PartAttribute

{

if (Visibility==Public)

StdOut.write (Name, NL);

}

}

· "NL" indicates the return.

· "StdOut" is the standard output which will generally be the Objecteering output window.

· "write" is a method of writing, which allows an unlimited number of parameters, which can be character strings or other basic types (integer, boolean, etc).

· "PartAttribute" is the concatenation of the "Part" role name, and the "Attribute" metaclass name. For J, and from a "Class" instance perspective, it designates all attributes belonging to the current class. "Name" is the attribute of the "Attribute" metaclass.