Please help me with the fallowing polymorphic example

Question

Hy,

Please help me with the folowing polymorphic example:

    interface Car {}
    class Toyota implements Car {}
    class ToyotaSUV extends Toyota {}
    class Drive {
public static void main(String [] args){
          Car c = new Car();
          Toyota t = new ToyotaSUV();
          Car s = new ToyotaSuv();

}

Which of the above can and can't be instantiated?

ToyotaSUV can be a Toyota or/and Car?

Sincerely,

`Car` is an abstract interface class. `Toyota` is a base class of `Car`, and `ToyotaSUV` is a subclass that derives from the `Toyota` class. That being said, you *cannot* instantiate a pure abstract class, which is what `Car` is. — Cory Kramer, Sep 26 '14 at 17:23
What you wrote above is fine (have you tried?). Basically you can cast an instance "up", meaning - refer to toyota as a car. But not the other way around since not every car is a toyota. — Dror Fichman, Sep 26 '14 at 17:26
@DrorFichman No it is not fine. `Car c = new Car();` is bad, they are trying to instantiate a pure abstract class, that is not allowed. — Cory Kramer, Sep 26 '14 at 17:26
You're right obviously.. I was looking at the polymorphic part. — Dror Fichman, Sep 26 '14 at 17:29

score 1 · Accepted Answer · answered Sep 26 '14 at 17:26

1

You can't instantaite an interface, that is, you can't instantiate "Car". Interfaces can't be instantiated because they don't have a constructor.
ToyotaSUV IS a Toyota AND can behave as a Car. By the moment you extend ToyotaSUV you are saying that ToyotaSuv IS a Toyota and can do exaclty the same things that Toyota can. Also, as Toyota can behave as a Car beacause it implement that interface, you are saying that ToyotaSUV can behave as a Car too, beceause it also inheritance those methods.

answered Sep 26 '14 at 17:26

Rodrigo Aguirre Vanda

92
6

You can't say that ToyotaSuv d = new Car()? – SocketM Sep 26 '14 at 17:42
No, you can´t do that, otherwise you would be instatiating an interface (Car). What you can do is Car c = (Car) new ToyotaSUV() – Rodrigo Aguirre Vanda Sep 26 '14 at 19:07

Please help me with the fallowing polymorphic example

1 Answers1