C# abstract关键字

using System;

public abstract class Vehicle {
   public abstract void display();
}

public class Bus : Vehicle {
   public override void display() {
      Console.WriteLine("Bus");
   }
}

public class Car : Vehicle {
   public override void display() {
      Console.WriteLine("Car");
   }
}

public class Motorcycle : Vehicle {
   public override void display() {
      Console.WriteLine("Motorcycle");
   }
}

public class MyClass {
   public static void Main() {
      Vehicle v;
      v = new Bus();
      v.display();
      v = new Car();
      v.display();
      v = new Motorcycle();
      v.display();
   }
}