Question

The following code has a problem with polymorphism. I keep getting a runtime error.

Error: "An unhandled exception of type System.InvalidCastException occured in polymorphism.exe"

Apparently, I need one line of code to fix it.

C# Code:

class Sensor

    {

        private string sensorName;

        public Sensor(string _name)

        {

            sensorName = _name;

        }

        public virtual void ActionType()

        {

            Console.WriteLine("Sensor Detect Nothing.");

        }

}

class SmokeSensor : Sensor

    {

        private string type;

        public SmokeSensor(string _type, string _name) : base(_name)

        {

            type = _type;

        }

        public override void ActionType ()

        {

            Console.WriteLine("Somke Sensor Detect Smoke.");

        }

    }

class Program

    {

        static void Main(string[] args)

        {

            Sensor super1, super2;

            SmokeSensor sub1, sub2;

            super1 = new Sensor("Sensor");

            sub1 = new SmokeSensor("Smoke", "Smoke Sensor");

            super2 = super1;

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ \\Tip: this is where the code should go.

            sub2 = (SmokeSensor)super1;

       }

    }

Answer 1

One line of code is :

super1 =(Sensor)sub1;

using System;

class Sensor

{

private string sensorName;

                public Sensor(string _name)

{

                  sensorName = _name;

              }

public virtual void ActionType()

{

   Console.WriteLine("Sensor Detect Nothing.");

}

}

class SmokeSensor : Sensor

{

private string type;

              public SmokeSensor(string _type, string _name) : base(_name)

{

   type = _type;

}

public override void ActionType ()

{

Console.WriteLine("Somke Sensor Detect Smoke.");

}

}

class Program

{

   static void Main(string[] args)

{

Sensor super1, super2;

SmokeSensor sub1, sub2;

super1 = new Sensor("Sensor");

super1.ActionType();

sub1 = new SmokeSensor("Smoke", "Smoke Sensor");

sub1.ActionType();

super2 = super1;

super2.ActionType();

super1 =(Sensor)sub1;

super1.ActionType();//When a derived class overrides a virtual member,

//that member is called even when an instance of that class is being accessed

//as an instance of the base class

sub2 = (SmokeSensor)super1;

sub2.ActionType();

}

}