ArcGIS Engine Developer Guide

CLASSES AND RELATIONSHIPS
There are three types of classes shown in the UML diagrams: abstract classes,
coclasses, and classes.
abstract
class
Instantiation
Type
inheritance
coclass
Composition
class
Association
1..*
Multiplicity
A coclass represents objects that you can directly create using the object declaration
syntax in your development environment. In Visual Basic, this is written
with the Dim pFoo As New FooObject syntax.
Dim pWSName as iworkspacename
Set pwsname = new workspacename
Dim pPoint as iPoint
Set pPoint = new Point
'Declare the interface you will use to
access the object
'Creates a new instance of the
WorkSpaceName class
The example discussed here—primary and
secondary line classes that each meet the
specification of the abstract line class—is an
illustration of type inheritance. Type inheritance
is discussed in detail later in this appendix.
To keep the object model diagrams as simple
and usable as possible, only key relationships, or
associations, are shown.
Dim pGeometry as iGeometry
Set pGeometry = new Point
A class can’t directly create new objects, but objects of a class can be created as a
property of another class or by functions from another class.
Dim pName as IName
Dim pFeatClass As IFeatureClass
Set pFeatClass = pName.Open
An abstract class can’t be used to create new objects; it is a specification for subclasses.
An example is that a “line” could be an abstract class for “primary line”
and “secondary line” classes. Abstract classes are important for developers who
want to create a subclass of their own; they show which interfaces are required
and which are optional for the type of class they are implementing. Required
interfaces must be implemented on any subclass of the abstract class to ensure the
new class behaves correctly in the ArcObjects system.
Dim pGeometry as IGeometry
Set pGeometry = New Point
If typeof pGeometry is IGeometry the
Msgbox "This is a Geometry object"
End if
RELATIONSHIPS
Among abstract classes, coclasses, and classes, there are several types of class
relationships possible—associations, type inheritance, instantiation, composition,
and n-ary associations.
Associations
Associations represent relationships between classes. They have defined multiplicities
at both ends.
Appendix A • Reading the object model diagrams • 443