public class Casting {
    public static void main(String[] args) {

	Thing[] things = {new Apple(), new Apple(), new Water()};
	
	for (int i = 0; i < things.length; i++) 
	    things[i].eat();

	for (int i = 0; i < things.length; i++) {
	    if (things[i] instanceof Water)
		((Water) things[i]).swallow();
	    /*try also this:*/ // things[i].swallow(); // not allowed
	}
    }
    
}

class Thing { 
    void eat() {
	System.out.println("Eat "+this.getClass().getName());
    } 
}

class Apple extends Thing { }

class Water extends Thing{ 
    void swallow() {
	System.out.println("Swallow "+this.getClass().getName());
    }
}

/* Output:
   Eat Apple
   Eat Apple
   Eat Water
   Swallow Water
*/