public static void main(String[] args) {
		ArrayList apples = new ArrayList();
		
		for (int i = 0; i < 3; i++)
			apples.add(new Apple());
		
		// Not prevented from adding an Orange to apples:
		apples.add(new Orange());
		
		for (int i = 0; i < apples.size(); i++)
			((Apple) apples.get(i)).id();
		// Orange is detected only at run time
	}