Question

Aditya is a co-worker of yours at Company ABC. Aditya has a problem with his C# code caused by his use of Polymorphism. The code can be compiled but is throwing a runtime error as shown below. Could you help Aditya to figure out what is the reason? State what the problem is and add one line of code to correct the problem.

An unhandled exception of type 'System.InvalidCastException' occurred in polymorphism.exe Additional information: Unable to cast object of type 'polymorphism.Sensor' to type 'polymorphism.SmokeSensor'. Break when this exception type is thrown Open Exception Settings Break Continue Ignore

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;

       }

    }

One line of code needs to be added to make this run correctly. How do I make it so (SmokeSensor)super1 can correctly be casted to sub2?

Thanks ;)

Answer 1

Problem:

Trying to convert object of type Sensor class(Base Class) to SmokeSensor class(Child Class). Which is illegal in C-Sharp.

Solution:

Applying Downcasting process will solve the problem.

Initially Base class object "super1" should be converted to SmokeSensor class Type as follows:

super1 = sub1;

___________________________________________________________________

Updated 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;
  
//Downcasting by converting Sensor class object(Base Class Object) to SmokeSensor class object(Child class Object)
super1 = sub1;
  
sub2 = (SmokeSensor)super1;
}
}

____________________________________________________________________________________________

Sample Run:

Livec Run it (F8) Save it Show compiler warnings [ + ] Show input Compilation time: 0,14 sec, absolute running time: 0,14 sec, cpu time: 0,12 sec, average memory usage: 14 Mb, average nr of threads: 3, absolute service time: 0,29 sec