OOP: Polymorphism & Interfaces

C# provides two abstraction frameworks:

• Abstract Class: A class declared `abstract` that cannot be instantiated. Can contain constructor fields, instance states, and fully defined methods.
• Interface: A contract definition. Interfaces contain no instance fields (only static final constants) and by default specify abstract signatures. Classes implement interfaces using the `implements` keyword. A class can implement multiple interfaces.

Let's run a program illustrating interfaces and dynamic runtime dispatch polymorphism:

using System;

interface IDrivable {
    void Drive(); // Interface abstract method
}

class Car : IDrivable {
    public void Drive() {
        Console.WriteLine("Car is driving on roads.");
    }
}

class Boat : IDrivable {
    public void Drive() {
        Console.WriteLine("Boat is cruising on water.");
    }
}

class Program {
    static void Main() {
        IDrivable v1 = new Car();
        IDrivable v2 = new Boat();

        v1.Drive();
        v2.Drive();
    }
}