c# - Abstract class calling an abstract method

Question

Can anyone explain to me why this works the way it does. The output comes out to "Print This". But how does the base class call bar(), when there is no implementation.

abstract class Base
{
    protected virtual void foo()
    {
        bar();
    }

    protected abstract void bar();
}

class Sub : Program
{
    protected override void foo()
    {
        base.foo();
    }

    protected override void bar()
    {
        Console.WriteLine("Print This");
    }

    static void Main(string[] args)
    {
        Sub obj = new Sub();

        obj.foo();
    }
}

Answer 1

That's the whole point of an abstract class: that it will only ever exist concretely as an instance of the derived class(es). By declaring abstract methods or properties, it is simply forcing the derived class(es) to provide concrete implementations of those members. In this way, if you have an instance of type Base, you can call myInstance.bar and you know that the derived class has implemented it because it wouldn't compile otherwise.

By the way, use pascal case when naming methods, i.e. Foo and Bar.