> Amarnath P wrote:
>
> hi andrea,
>
> can u explain more clearly about the lack of OO principles, that
> u have mentioned below ?????
The basic principle of having a factory class that creates unknown
instance objects with a common base class. For example, I have a factory
public class ShapeFactory {
public Shape createShape(String name);
}
and
public interface Shape {
}
And a bunch of shape objects:
public class Cone extends Shape {}
public class Box extends Shape {}
public class Sphere extends Shape {}
I cannot create an EJB home interface that generates me a different
instance object depending on the parameter that I pass to the
ejbCreate() method. That is, the following home interface is illegal:
public interface ShapeHome extends EJBHome {
public Shape create(String name);
}
because it is required to return an instance of the Shape class eg
public class ShapeEJB implements EntityBean {}
These classes cannot be cast to a narrower definition to get something
more useful.
EJBs do allow something similar, but not quite as flexible. What you
would have to do is create a bunch of home interfaces that were similar,
but registered under different JDNI context names. This would given you
almost a factory, but instead of using a method that takes a string name
in the create, you would have to look up the home interface for a
dynamically created context name. eg
public class MyShapeUtils {
public static Shape createShape(string name) {
String ctx_name = "ejb/shapes/" + name;
InitialContext ctx = new InitialContext();
ShapeHome home = (ShapeHome)ctx.lookup(ctx_name);
Shape shape = home.create();
return shape;
}
}
--
Justin Couch http://www.vlc.com.au/~justin/
Freelance Java Consultant http://www.yumetech.com/
Author, Java 3D FAQ Maintainer http://www.j3d.org/
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- Greg Bear, Slant
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