Is this how i'm suppose to use subclasses?

Question

I have this code, and it works, but for it to work, it has to generate exceptions, which I catch, but its weird having a function that in order to work properly always generates exceptions. Is this the way I'm suppose to do this?
               for (FObject i : objects)
                    try
                         FUnit unit = (FUnit)i;
                         unit.moveTowardPoint();
                    }catch(ClassCastException e)
               }objects is an Array of FObjects. FObject is a class with a few functions and protected fields. FUnit is a class that extends FObject and adds the function "moveTowardPoint()" this code works to call moveTowardPoint on all of the FObjects that in objects that are FUnits, but it has to throw exceptions, which I catch.
What I'm trying to ask is, is this type of casting a normal ocurance in Java programming? Does it have any issues, or problems?
Edited by: happypigface on Mar 27, 2008 8:13 PM

Answer 1

You can use the instanceof operator to find out whether the FObject is an FUnit, and only do the cast and method call conditionally. No try/catch required.
But it would be better still if you reworked your code so the caller doesn't need to know what kind of object it has (apart from what would be clear from static type checking, that is, an array or list of FObject).
So maybe you could do:
class FObject {
  void tick() {
    // do stuff common to all FObjects
  // etc
class FUnit {
  void tick() {
    super.tick();
    moveToUnit();
  // etc
}Then your loop is just:
for (FObject i: objects)
  i.tick();