CODEWITHSUNDEEP
c#
Mohit Tomar
Mohit Tomar

Reputation: 192

Why is dynamic binding not working the way I expect it to in the following code?

I've read the following statement about dynamic binding:

Which method to invoke is determined by variable's actual type and not declared type. This is known as dynamic binding.

But then why is the following code not working the way I expect it to?

class Program
{
    static void Main(string[] args)
    {
        Parent parent = new Parent();
        parent.SomeMethod(); // overriden 
        parent.AnotherMethod(); // hidden

        Child child = new Child();
        child.SomeMethod();
        child.AnotherMethod();

        System.Console.WriteLine("---------------------------------------");

        Parent parent1 = new Child();
        parent1.SomeMethod();
        parent1.AnotherMethod();


    }
}

class Parent
{
    public virtual void SomeMethod() //override
    {
        System.Console.WriteLine("Parent.SomeMethod");
    }

    public void AnotherMethod() //hide
    {
        System.Console.WriteLine("Parent.AnotherMethod");
    }
}

class Child : Parent
{
    public override void SomeMethod() //overriden
    {
        System.Console.WriteLine("Child.SomeMethod");
    }

    public new void AnotherMethod() //hidden
    {
        System.Console.WriteLine("Child.AnotherMethod");
    }

}

The output of the above code is:

Parent.SomeMethod

Parent.AnotherMethod

Child.SomeMethod

Child.AnotherMethod

Child.SomeMethod

Parent.AnotherMethod <-- Shouldn't this be Child.SomeMethod? I'm confused please explain

Upvotes: 2

Views: 170

Answers (2)

Sumit Singh
Sumit Singh

Reputation: 15906

From New Vs Override

You cannot override a non-virtual or static method. The overridden base method must be virtual, abstract, or override.

From new modifier (C# Reference)

Upvotes: 2

StuartLC
StuartLC

Reputation: 107387

You are upcasting variable parent1 back to class type Parent in this assignment:

Parent parent1 = new Child();

Because AnotherMethod isn't polymorphic (since you haven't applied virtual / override), and in fact you've explicitly added the new keyword to tell the compiler that the AnotherMethod symbol is reused between Child and Parent (i.e. There's no dynamic binding on AnotherMethod).

As a result, compiler will resolve the Parent's AnotherMethod symbol at compile time because of the variable type (Parent parent1), irrespective of the fact that the actual run time type allocated on the heap is a Child instance.

You can access the Child AnotherMethod by using another downcast:

((Child)parent1).AnotherMethod();

Upvotes: 2

Related Questions