Question

public class Car {

    String color;

    public void thisIs(){
        System.out.println("Calling method from Car: the color is " + color);
    }

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }
}

public class BMW extends Car {

    public void thisIs(){
        System.out.println("Calling method from BMW: the color is " + color);
    }
    public Car toCar(){
    Car newCar = new Car();
    newCar.setColor(this.color);
    return newCar;
}

}

public class AbstractTest {

    public static void main(String args[]){
        Car aCar = new Car();
        aCar.setColor("Red");
        aCar.thisIs();

        BMW aBMW = new BMW();
        aBMW.setColor("Black");
        aBMW.thisIs();

        //Car aaCar = new Car();
        //aaCar = (Car)aBMW;
        //aaCar.thisIs();

            Car aaCar = aBMW.toCar();
    aaCar.thisIs();
    }
}

I expect the result to be:

Calling method from Car: the color is Red

Calling method from BMW: the color is Black

Calling method from Car: the color is Black

But, the result I got is:

Calling method from Car: the color is Red

Calling method from BMW: the color is Black

Calling method from BMW: the color is Black

Where am I wrong?
And how can I use the method from the super class to get the data in a subclass object?
I can write a toCar() method in BMW class to do this.
But, why casting doesn’t work?
Thanks ahead!

OK! Thank you!

I got why casting doesn’t work.

So, I add a method in BMW toCar() to get the result I want.

Answer 1

Casting the object does not change the nature of the object. It is still a BMW object; casting just tells the compiler to treat it as though it were a Car object.

As long as we’re on the subject of inheritance: there is NO need to put either the color variable or the get/setColor methods into both the super and subclass. Putting them in the car class means they are available in any subclass; they are superfluous and a bit confusing in the subclass. I would take them out entirely.