Casting without "explicit" coding

Question

Hi,
I have some problem with casting. Here is the code:
* public interface ViewInt...
* public class View extends JInternalFrame implements ViewInt...
* public class View2 extends JInternalFrame implements ViewInt...
* public class Main
ViewInt frame=new View();
In some other class, I need to add this frame into a DesktopPane,
but his code isn't work
this.getDesktopPane().add(frame);
because the method add(ViewInt) doesn't exist!
But it works like this: this.getDesktopPane().add((View)frame);
My problem is that in this class, we are not supposed to know the class View!
How can I make this work with View2 too or another classes without instanceof because it is supposed to accept any class which extends JInternalFrame?
I try this but doesn't work: this.getDesktopPane().add((frame.getClass())frame);
Any idea?

Answer 1

Option 1: Add a common view class, so that you can refer to both objects through the same reference, i.e.
public interface ViewInt {...}
public abstract class AbstractView extends JInternalFrame implements ViewInt {}
public class View extends AbstractView {...}
public class View2 extends AbstractView {...}
public class Main {
    AbstractView frame=new View();
        getDesktopPane().add(frame);
}Using this approach, you can refer to either type of view using the same reference, and they are both Frames and ViewInts. However, your code is still aware of the View class, albeit through a new common base class.
Option 2: Make the interface aware of the fact that it'll be implemented mixin with a Frame, and have it provide access to this Frame, i.e.
public interface ViewInt {
    JInternalFrame asJInternalFrame();
public class View extends JInternalFrame implements ViewInt {
    public JInternalFrame asJInternalFrame() { return this; }
public class View2 extends JInternalFrame implements ViewInt {
    public JInternalFrame asJInternalFrame() { return this; }
public class Main {
    AbstractView frame=new View();
        getDesktopPane().add(frame.asJInternalFrame());
}Using this approach, you can refer to either type of view using the same reference, but they are not Frames, only ViewInts. However, your code can still access the frame.
Any other classes implementing this interface must support this method. They could throw an UnsupportedOperationException, and this approach is a bit messy in that it mixes the model and the view. However, you're already mixing the two by expecting to be able to be able to add a model object as a view object.