C#•13mo ago

can someone help me with my abstract class

I've created my abstract classes and no we can't make instances of them, but i keep getting errors even after following youtube videos to the t. here's my first file using abstract classes

namespace Module_9
{
    public abstract class RailroadCar
    {
        //data fields
        protected double length;

        //constr
        protected RailroadCar(double length = 0.00)
        {
            SetLength(length);
        }

        //GETTERS
        /** Returns length of solid.
            @return: solid length
        */
        public double GetLength(double length) { return length; }

        /** Updates length of solid.
            @return: updated length.
        */
        //SETTERS
        public void SetLength(double length) { this.length = length;}

        /** Calculates the volume of the solid.
            @return: calculated volume of the solid
        */
        public abstract double Volume();
    }
}

namespace Module_9
{
    public abstract class RailroadCar
    {
        //data fields
        protected double length;

        //constr
        protected RailroadCar(double length = 0.00)
        {
            SetLength(length);
        }

        //GETTERS
        /** Returns length of solid.
            @return: solid length
        */
        public double GetLength(double length) { return length; }

        /** Updates length of solid.
            @return: updated length.
        */
        //SETTERS
        public void SetLength(double length) { this.length = length;}

        /** Calculates the volume of the solid.
            @return: calculated volume of the solid
        */
        public abstract double Volume();
    }
}

25 Replies

DinnyOP•13mo ago

in my main program, i know we can't do, for example, " RailroadCar railroadcar = new RailroadCar()," but in the exmple on youtube, i could do something like "RailroadCar railroadcar = new TankCar();" but that doesn't work either. I am still new and trying to understand, but I am so stuck

Angius•13mo ago

Does TankCar inherit from RailroadCar?

DinnyOP•13mo ago

yes it does one moment

Angius•13mo ago

It has to work, then

MODiX•13mo ago

Angius

REPL Result: Success

abstract class Foo {}
class Bar : Foo {}

Foo f = new Bar();

abstract class Foo {}
class Bar : Foo {}

Foo f = new Bar();

Compile: 566.461ms | Execution: 36.685ms | React with ❌ to remove this embed.

DinnyOP•13mo ago

namespace Module_9
{
    public abstract class TankCar : RailroadCar
    {
        //data fields
        private double radius;

        protected TankCar(double radius, double length) : base(length)
        {
            SetRadius(radius);
            SetLength(length);

        }

namespace Module_9
{
    public abstract class TankCar : RailroadCar
    {
        //data fields
        private double radius;

        protected TankCar(double radius, double length) : base(length)
        {
            SetRadius(radius);
            SetLength(length);

        }

here's a tiny bit og tankcar of i don't see what I am doing wrong then

Angius•13mo ago

Your constructor is protected, that might be why you're getting errors

DinnyOP•13mo ago

bc i keep getting the same error :///

Angius•13mo ago

But it's hard to tell without seeing the actual error

DinnyOP•13mo ago

ill take a picture of it one momebt plz

DinnyOP•13mo ago

DinnyOP•13mo ago

should they all be public instead of protected ?

Angius•13mo ago

Ah Well Your TankCar itself is abstract And, as you said, can't instantiate abstract classes

DinnyOP•13mo ago

one moment lemme try fixing that okay i made them now a public class derived from the abstract classes but it’s still not working

Angius•13mo ago

Is the derived class still abstract?

DinnyOP•13mo ago

yes that's how my prof is doing it too

Angius•13mo ago

It's not It cannot be Because instantiating an abstract class is not possible The base class can be abstract But classes that inherit from it can be not-abstract

DinnyOP•13mo ago

oh no wait sorry the base class is abstract the derived classes are not they're all public

Angius•13mo ago

And in your example the derived class is still abstract Hence the error

DinnyOP•13mo ago

oh wait let me show up my updated version

namespace Module_9
{
    public abstract class RailroadCar
    {
        //data fields
        private double length;

        //constr
        protected RailroadCar(double length = 0.00)
        {
            SetLength(length);
        }

        //GETTERS
        /** Returns length of solid.
            @return: solid length
        */
        public double GetLength() { return length; }

        /** Updates length of solid.
            @return: updated length.
        */
        //SETTERS
        public void SetLength(double length) { this.length = length;}

        /** Calculates the volume of the solid.
            @return: calculated volume of the solid
        */
        public abstract double Volume();
    }
}

namespace Module_9
{
    public abstract class RailroadCar
    {
        //data fields
        private double length;

        //constr
        protected RailroadCar(double length = 0.00)
        {
            SetLength(length);
        }

        //GETTERS
        /** Returns length of solid.
            @return: solid length
        */
        public double GetLength() { return length; }

        /** Updates length of solid.
            @return: updated length.
        */
        //SETTERS
        public void SetLength(double length) { this.length = length;}

        /** Calculates the volume of the solid.
            @return: calculated volume of the solid
        */
        public abstract double Volume();
    }
}

here's the base abstract class

namespace Module_9
{
    public class TankCar : RailroadCar
    {
        //data fields
        private double radius;

        public TankCar(double radius = 0.0, double length = 0.0) : base(length)
        {
            SetRadius(radius);
            SetLength(length);

        }

        //GETTERS
        /** Returns radius of solid.
            @return: solid radius.
        */
        public double GetRadius() { return radius; }



        //SETTERS
        /** Updates radius of solid.
            @return: updated radius
        */
        public void SetRadius(double radius) { this.radius = radius; }

        /** Calculates the volume of the solid.
            @return: calculated volume of the solid
        */
        public override double Volume() { return Math.PI * Math.Pow(radius, 2) * GetLength(); } 
    }
}

namespace Module_9
{
    public class TankCar : RailroadCar
    {
        //data fields
        private double radius;

        public TankCar(double radius = 0.0, double length = 0.0) : base(length)
        {
            SetRadius(radius);
            SetLength(length);

        }

        //GETTERS
        /** Returns radius of solid.
            @return: solid radius.
        */
        public double GetRadius() { return radius; }



        //SETTERS
        /** Updates radius of solid.
            @return: updated radius
        */
        public void SetRadius(double radius) { this.radius = radius; }

        /** Calculates the volume of the solid.
            @return: calculated volume of the solid
        */
        public override double Volume() { return Math.PI * Math.Pow(radius, 2) * GetLength(); } 
    }
}

heres the TankCar class

Angius•13mo ago

Now it should work

DinnyOP•13mo ago

why is there still a squiggle ugh lemme refrsh plz hold

Angius•13mo ago

What does the squiggle say?

DinnyOP•13mo ago

okay i just needed to save and refresh VS does that soemetines, it's annoying tysm !! u were a big help

Angius•13mo ago

Anytime

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can someone help me with my abstract class