Our first example

Aims of the program example

In this example, we are going to develop a program that lists the names of the classes of the package ("Package" metaclass), and for each class, provides a list of public methods.

Realization principle

The J method, which we will call "listClasses", must be defined on the "Package" metaclass. This method will run through all the classes of the package that is being processed, and for each class, it will list methods with public visibility.

Note: This example is for the "listClasses" command on packages.

J program

Package:listClasses () Method definition

{

OwnedElementClass // Going through the Package

classes

{

StdOut.write(NL, "CLASS:", Name);

PartOperation.<select (Visibility == Public)

// Going through the method's public classes

{

StdOut.write(NL, " Public method:", Name);

}

}

} // End of "listClasses

Description of the terms used

Term	Nature	Definition
Package	Metamodel class	Package
NL	Constant	Return (New Line)
OwnedElementClass	object (Class[ ])	Classes of the current package
StdOut	Predefined variable	Standard output
PartOperation	object(Operation[ ])	The operations of the class
Visibility	object - (String attribute)	Visibility of an operation
Name	object - (String attribute)	Name of the current object
listClasses	J method	Defined method
String	basic class	Character string
write	Predefined method	Writing in a file

Execution

If a "Human_Society" package is composed of "Man" and "Woman" classes with the "walk" and "eat" methods, the "listClasses" message sent to the "Human_Society" object will give the following result:

CLASS: Man

Public method :eat

Public method :walk

CLASS: Woman

Public method :eat

Public method :walk