C#中判断空字符串的几种方法

 1namespace my
 2{
 3    class Program
 4    {
 5        static void Main(string[] args)
 6        {
 7            string a = string.Empty;
 8            if (a == "") //执行效率(4)
 9            {
10                Console.WriteLine(@"a=="" ");
11            }
12            if (a == string.Empty)//执行效率(3)
13            {
14                Console.WriteLine("a==string.Empty");
15            }
16            if (a.Length == 0)  //执行效率最高(1)
17            {
18                Console.WriteLine("a.Length == 0");
19            }
20            if (string.IsNullOrEmpty(a)) //执行效率(2) 
21            {
22                Console.WriteLine("a==string.Empty");
23            }
24
25           bool b =  IsNullOrEmpty(a);
26           Console.WriteLine(b);
27
28        }
29
30        /**//// <summary>
31        /// 判断字符串是否为空
32        /// </summary>
33        /// <param name="value">String 类型的值</param>
34        /// <returns>返回值 true ,false </returns>
35        public static bool IsNullOrEmpty(string value)
36        {
37            if (value != null)
38            {
39                return (value.Length == 0);
40            }
41            return true;
42        }
43
44    }
45}