ArcGIS Engine Developer Guide

JAVA APPLICATION PROGRAMMING INTERFACE
provide an implementation to those interfaces. For each abstract class in
ArcObjects there are subclasses that provide the implementation.
A class cannot be publicly created in ArcObjects; however, objects of this class
type can be created as a property of another class or instantiated by objects from
another class. In the ArcGIS API for Java, the default constructor normally used
to create a class is undefined for ArcObjects classes.
/* The constructor for FeatureClass() is unsupported. */
FeatureClass fc = new FeatureClass(); // incorrect usage
The following example illustrates this behavior while guiding you through the
process of opening a feature class.
IWorkspaceFactory wf = new ShapefileWorkspaceFactory();
IFeatureWorkspace fw = new
IFeatureWorkspaceProxy(wf.openFromFile("\\path\\to\\data", 0));
/* Create a Feature Class from FeatureWorkspace. */
IFeatureClass fc = fw.openFeatureClass("featureclass name");
In ArcObjects, a coclass is a publicly creatable class. This means that you can
create your own objects merely by declaring a new object as shown below.
/* Create an Envelope from the Envelope coclass. */
Envelope env = new Envelope();
Structs
A structure defines a new data type made up of elements called members. Java
does not have structures as complex data types. The Java language provides this
functionality through classes; you can simply declare a class with the appropriate
instance variables. For each structure in ArcObjects, there is a representative Java
class with publicly declared instance variables matching the structure members as
outlined below.
ArcObjects Struct
struct WKSPointZ
double x
double y
double z
}
Java Representation
public class _WKSPointZ {
public double x;
public double y;
public double z;
}
You can work with these classes like any other class in Java:
_WKSPointZ pt = new _WKSPointZ();
pt.x = 2.23;
pt.y = -23.14;
pt.z = 4.85;
System.out.println(pt.x + " " + pt.y + " " + pt.z);
Enumerations
Versions of the Java 2 SDK prior to version 5 do not have enum types. To emulate
enumerations in Java, a class or interface must be created that holds constants.
For each enumeration in native ArcObjects, there is a Java interface with
publicly declared static integers representing the enumeration value.
Chapter 4 • Developer environments • 187