C#双端队列类

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();
   } 
}