CastShowcase.java

class Ship {
    public String name;
    public int weight;

    public Ship(String name_, int weight_) {
        name = name_;
        weight = weight_;
    }

    public String toString() {
        return "Ship “" + name + "”, weight: " + weight;
    }
}

class CargoShip extends Ship {
    public CargoShip(String name_, int weight_) {
        super(name_, weight_);
    }
    public void pickUpCargo() {
        System.out.println(name + " + 100 t");
        weight += 100;
    }
}

class CastShowcase {
    public static void main(String[] args) {
        Ship[] ships = {
            new CargoShip("Boaty McBoatFace", 20000),
            new CargoShip("Sir David Attenborough", 30000),
            new CargoShip("Titanic", 52310)
        };
        for (Ship s : ships) {
            System.out.println(s);
        }
        CargoShip cs = (CargoShip)ships[0];
        cs.pickUpCargo();
        // INVALID: for (CargoShip s : ships) {
        for (Ship s : ships) {
            ((CargoShip)s).pickUpCargo();
        }
        for (Ship s : ships) {
            System.out.println(s);
        }
    }
}