CODEWITHSUNDEEP
c#inheritancevirtual-functions
Joe Dugan
Joe Dugan

Reputation: 119

I don't understand what they mean when runtime will decide which overriden method gets called

polymorphism example:

public class animal 
{
    public void virtual speak()
    {
        Console.WriteLine("Animals can speak in many ways.");
    }
}

public class dog : animal 
{
    public void override speak()
    {
        Console.WriteLine("I bark!");
    }
}

static void main()
{
    animal doggy = new dog();

    doggy.speak();
}

output:

I bark!

I keep reading that the correct speak method is called during runtime, but is it not already hard coded and does the compiler not recognize which method it will invoke based on the virtual and override keywords?

Upvotes: 0

Views: 81

Answers (2)

Ed Swangren
Ed Swangren

Reputation: 124642

Your compiler doesn't necessarily know which implementation will be the underlying type. Take, for example:

class A
{
    public virtual void F() { Console.WriteLine("A"); }
}

class B : A
{
    public override void F() { Console.WriteLine("B"); }
}

class Program
{
    static A GetImpl(int i)
    {
        switch(i)
        {
            case 1:
                return new A();
            case 2:
                return new B();
            default:
                // whatever
        }
    }

    static void Main(string[] args)
    {
        var i = int.Parse(Console.ReadLine());
        A a = GetImpl(i);
        a.F();
    }
}

How could the compiler possibly know if an A or a B is returned? It cannot, so the task of calling the correct method is delegated to the runtime.

Upvotes: 3

John3136
John3136

Reputation: 29265

If your code was something like

Animal anAnimal= NoahsArc.getNextAnimal();
anAnimal.speak();

Now you don't actually know what sort of animal you are going to get, so the runtime ensures the correct speak method is called.

Upvotes: 1

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