Re: ...inheritance and calling the grandchild not the childs implementation

So I have (skipping some detail) the following:

public abstract class BaseObject implements IObject {

   public abstract void setMethod();
}

public class ChildObject extends BaseObject implements IObject {
    public void setMethod() {
        // Child implementation
    }
}

public class GrandChildObject extends ChildObject {
    @override
    public void setMethod() {
        // grand Child implementation
    }
}

then when I am in a method

public void testThis(Object o) {

    ((IObject) o).setMethod();

}

it executes the ChildObjects implementation

so I tried this

public void testThis(Class GrandChildClass, Object o) {
   IBaseObject myObject = (IBaseObject) GrandChildClass.cast(o);
   myObject.setMethod();
}

but it still executes the Child method!

How can I execute the GrandChild method from testThis without directly
casting it to a grand child?

thanks

Tim