You can always downcast in the presence of an instanceof case statement:

   ArrayList myList = new ArrayList(new Object[] { "foo", 42, new Bar() });
   for(Object elem : myList) {
      if(elem instanceof String) doStringThing((String) elem);
      else if(elem instanceof Number) doNumberThing((Number) elem);
      else if(elem instanceof Bar) doBarThing((Bar) elem);
      else doObjectThing(elem);
   }

Or you could keep elements as Objects until you needed to perform a specific operation on them, then cast at the site and perform the operation, letting the ClassCastException propagate if you're wrong. This is basically what Arc does.