今天在浏览DevTopics的博客时,发现一篇介绍String的随笔,介绍的是判断一个String变量是否为空时,String的一个方法和一个属性之间的比较,给一个 string变量 's', 下面那个表达式更快?

1.  String.IsNullOrEmpty( s ) 
2.  s == null || s.Length == 0

如果你猜第二个,那么你是对的. 它将比String.IsNullOrEmpty方法快15%,但这种也是以百万分之一秒来衡量的!
这里有一个简单的例子来比较2种方式:

using System;

namespace StringNullEmpty
{
    class Program
    {
        static void Main( string[] args )
        {
            long loop = 100000000;
            string s = null;
            long option = 0;
            long empties1 = 0;
            long empties2 = 0;

            DateTime time1 = DateTime.Now;

            for (long i = 0; i < loop; i++)
            {
                option = i % 4;
                switch (option)
                {
                    case 0:
                        s = null;
                        break;
                    case 1:
                        s = String.Empty;
                        break;
                    case 2:
                        s = "H";
                        break;
                    case 3:
                        s = "HI";
                        break;
                }
                if (String.IsNullOrEmpty( s ))
                    empties1++;
            }

            DateTime time2 = DateTime.Now;

            for (long i = 0; i < loop; i++)
            {
                option = i % 4;
                switch (option)
                {
                    case 0:
                        s = null;
                        break;
                    case 1:
                        s = String.Empty;
                        break;
                    case 2:
                        s = "H";
                        break;
                    case 3:
                        s = "HI";
                        break;
                }
                if (s == null || s.Length == 0)
                    empties2++;
            }

            DateTime time3 = DateTime.Now;

            TimeSpan span1 = time2.Subtract( time1 );
            TimeSpan span2 = time3.Subtract( time2 );
            Console.WriteLine( "(String.IsNullOrEmpty( s )): Time={0} Empties={1}",
                span1, empties1 );
            Console.WriteLine( "(s == null || s.Length == 0): Time={0} Empties={1}",
                span2, empties2 );
            Console.ReadLine();
        }
    }
}
下面是结果:
(String.IsNullOrEmpty( s )): Time=00:00:06.8437500 Empties=50000000
(s == null || s.Length == 0): Time=00:00:05.9218750 Empties=50000000