Force the subclass

Question

as a tool to force the subclass to display the correct data?

class Program
{
    static void Main(string[] args)
    {
        var tran = new List<Transporte>();
        tran.Add(new Navio());   // Objetos das subclasses   
        tran.Add(new Aviao());   // podem pertencer   
        tran.Add(new Onibus());  // ao tipo da Superclasse.   
        Console.WriteLine(" exemplo aplicação polimorfismo .");
        for (int i = 0; i < tran.Count; i++)
        {
            tran[i].exibeDados();
        }
        Console.ReadKey();
    }
}

public class Transporte
{
    public void exibeDados()
    {
        Console.WriteLine("classe transporte: Método para exibição dos dados.");
    }
}

public class Aviao : Transporte
{
    // Sobreposição do método da superclasse
    public void exibeDados()
    {
        Console.WriteLine("Aviao");
    }
}

public class Navio : Transporte
{
    // Sobreposição do método da superclasse
    public void exibeDados()
    {
        Console.WriteLine("Navio");
    }
}

public class Onibus : Transporte
{
    public void exibeDados()
    {
        // Sobreposição do método da superclasse
        Console.WriteLine("Onibus");
    }
}

Answer 1

Adding the modifier virtual in the base class method and then doing the override in the derived class:

public class Transporte
{
    public virtual void exibeDados()
    {
        Console.WriteLine("classe transporte: Método para exibição dos dados.");
    }
}

public class Aviao : Transporte
{
    // Sobreposição do método da superclasse
    public override void exibeDados()
    {
        Console.WriteLine("Aviao");
    }
}

Thus, it is indicated that derivative classes that do not override of the method, print "transport class...".

Case knife override (as is the case for the Aviao class), when invoking the method exibeDados(), will execute what is in the derived class method (in this case print "Aviao").

Answer 2

To force the subclass implementing the method ExibeDados, the method must be abstract (marked with keyword abstract). Consequently, the class Transporte should also be abstract and as such can never be instantiated directly (which seems to me to be the desired, in this situation).

public abstract class Transporte
{
    public abstract void ExibeDados();
}

public class Aviao : Transporte
{
    public override void ExibeDados()
    {
        Console.WriteLine("Aviao");
    }
}

It seems to me that making the abstract class is the most indicated in this situation - the example of Transport VS Plane/Ship, and the example of Geometric Shape VS Square/Triangle are widely used to demonstrate situations where the base class should be abstract.

If the actual case is different from the question, and if the class cannot be abstract, then the answer is: it is not possible. A nonabstract class cannot force derived classes.

Note: the convention dictates that the name of the methods be written in Pascalcase, then the method should be called ExibeDados instead of exibeDados.