How statement 3 is false and 4 true

Question

class Vehical{}

public class Car extends Vehical {
    public static void main(String[] args) {

        Vehical v = new Vehical();
        Car c = new Car();

        boolean is =  v instanceof Vehical;
        System.out.println("is v instanceof Vehical class - "+is);

        is = c instanceof Car;
        System.out.println("is c instanceof of Car class - "+is);

        is = v instanceof Car;
        System.out.println("is v instanceof of Car class - "+is);

        is = c instanceof Vehical;
        System.out.println("is c instanceof of Vehical class - "+is);
    }
}

*Vehicles include wagons, bicycles, motor vehicles (motorcycles, cars, trucks, buses), railed vehicles (trains, trams), watercraft (ships, boats), amphibious vehicles (screw-propelled vehicle, hovercraft), aircraft (airplanes, helicopters) and spacecraft.* (wiki) Define more subclasses and you will see `v instanceof Car` doesn't always hold true — Andrew Tobilko, Feb 26 '20 at 14:36

score 1 · Answer 1 · answered Feb 26 '20 at 14:43

1

Vehicle isn't a Car because it is parent for a Car.
Car is implementation of Vehicle, so Car is Vehicle.

You can read more here: https://www.tutorialspoint.com/What-is-Is-a-relationship-in-Java

answered Feb 26 '20 at 14:43

Сергей Дзюбка

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9

Persixty · Answer 2 · 2020-02-28T12:32:52.103

Because v is a (concrete) Vehical (I think you mean vehicle).

But a 'concrete' instance of Vehical isn't a Car. It's a (non-specific) instance of Vehical. So v instanceof Car is false.

But c is a concrete instance of Car and because Car a sub-class of Vehical c is also a Vehical because all instances of Car are also instances of Vehical. So c instanceof Vehical is true because (in your model) all 'Car's are `Vehical's as well (implicitly by inheritance).

You can make Vehical an abstract class if you don't want instances of Vehical to exist that are not a more specific type of Vehical (e.g. Car, Motorbike?, Lorry?). In the real world there could never be a vehicle that isn't a specific kind of vehicle.

Nonsense: What do you drive? I drive a vehicle. What kind of vehicle? No particular kind, it's just a vehicle!

The recommended model would be to declare an interface called Vehical and implement it for each (more) concrete type of Vehical because this inheritance model can difficult to manage. But what you've done is valid.

How statement 3 is false and 4 true

2 Answers2