Dynamic typecasting for re-usability

Question

Hi there,
I'm trying to dynamically cast an object to a class only known at runtime. All that is known at compile time is the name and type of a variable inside the object - and that is all that is of interest. The reason for this is to create re-usable code to allow multiple classes to be used as peers (all owned by the unknown class) together.
I have a method (provided, so I can't change it) getOwner() that gives me the parent class, but as type Object. I need to re-cast it to the correct class to be able to access its content. I know ahead of time that the variable knownvar will exist in the parent class, and I know what type it will be.
So instead of doing:
if(this.getOwner().getType() == "ClassA")
  (ClassA)this.getOwner().knownvar = somevalue;
else if(this.getOwner().getType() == "ClassB")
  (ClassB)this.getOwner().knownvar = somevalue;
elseif ... (ad nauseum)I'd rather like to do something similar to this (this does not work):
(this.getOwner().getType())this.getOwner().knownvar = somevalue;In fact, I'd prefer not to do the whole list of elseifs if at all possible, since it limits possible future use to pre-thought of class names - and adding some that might not exist (also bad).
Any suggestions on how this can be done?

Answer 1

Thank you for the replies! (Especially Loko for that possible workaround)
Yes indeed, it is quite a bad design and I flinch at having to hack things so badly. It is not a clean and elegant design when done like this. Unfortunately I have no choice but to use a workaround. I'll try your suggestion and see if it can do the trick.
duffymo - As for using if checks - that is exactly what I don't want to use exactly because it is not object oriented - but is a way to express and explain to others what kind of function I am trying to perform. I'd perfer to use something like my second code snippet where no prior knowledge of the class is needed. I need to cast, otherwise the knownvar property is not accessable. Unfortunately, like I said, I do not have control over the interface, so I need a workaround.
There is also a small chance I might be able to convince the supplier of the owner class to implement this better by using an intermediate class that extends the one providing "Object getOwner()", returning a more specific class that expresses the presense of knownvar. I am using Java code fragments inside a third-party product, so it might not be possible to make this change within the timescales available.