public void doSomething(Collection c)
  {
    Iterator i = c.iterator();
    while (i.hasNext())
    {
      SomeClass d = (SomeClass) i.next();
      d.doSomething();
      d.doSomethingElse();
      if (d instanceof SomeSubClass)
      {
        ((SomeSubClass) d).doSomethingSpecial();
      }
    }
  }