C# Nullable 使用一例

using System;
using System.Collections.Generic;
using System.Text;

namespace Nullable
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("***** Fun with Nullable Data ******");
            DatabaseReader dr = new DatabaseReader();

            int? i = dr.GetIntFromDatabase();
            if (i.HasValue)
            {
                Console.WriteLine("Value of i is: {0}", i);
            }
            else
            {
                Console.WriteLine("Value of i is undefined.");
            }

            bool? b = dr.GetBoolFromDatabase();
            if (b != null)
            {
                Console.WriteLine("Value of b is: {0}", b);
            }
            else
            {
                Console.WriteLine("Value of b is undefined");
            }

            int? myData = dr.GetIntFromDatabase() ?? 100;
            Console.WriteLine("Value of myData: {0}", myData);
            Console.ReadLine();
        }
    }
    class DatabaseReader {
        public int? numbericValue;
        public bool? boolValue = true;

        public int? GetIntFromDatabase()
        {
            return numbericValue;
        }

        public bool? GetBoolFromDatabase()
        {
            return boolValue;
        }
    }
}