asoperator.cs

vc的原码例子12 vc的原码例子12

using System;

class clsPhone
{
	public clsPhone(string number)
	{
		Number = number;
	}

	public virtual void Dial(string NumberToCall)
	{
		System.Console.WriteLine("Beep, Beep: Tone Dial");

		System.Console.WriteLine("Calling {0}", NumberToCall);
	}

	protected string Number;
};



class clsRotaryPhone : clsPhone
{
	public clsRotaryPhone(string number) : base(number)
	{
		
	}

	public override void Dial(string NumberToCall)
	{
		System.Console.WriteLine("In Rotary Dial, calling: {0}", 
			NumberToCall);
	}
};


class clsAsOperator
{
	static void Main()
	{
		clsPhone BasePhone = new clsPhone("555-1212");
		clsRotaryPhone DerivedPhone  = new clsRotaryPhone("555-5555");

        // Try downcast
		DerivedPhone = BasePhone as clsRotaryPhone;

		if (DerivedPhone == null)
		  System.Console.WriteLine("DerivedPhone is NULL");
        else
          System.Console.WriteLine("BasePhone is downcast");
		  
		// Try downcast
		try 
		{
			DerivedPhone = (clsRotaryPhone) BasePhone;
		}
		catch (Exception e)
		{
		  System.Console.WriteLine("Invalid cast exception caught");
		}

		DerivedPhone  = new clsRotaryPhone("555-5555");

		// Try upcast
		BasePhone = DerivedPhone as clsPhone;

		if (BasePhone == null)
			System.Console.WriteLine("BasePhone is NULL");
		else
            System.Console.WriteLine("DerivedPhone has been upcast");

		try 
		{
			BasePhone = (clsPhone) DerivedPhone;
			System.Console.WriteLine("DerivedPhone again upcast");
		}
		catch (Exception e)
		{
			System.Console.WriteLine("Invalid cast exception caught");
		}
	}
}