我们通过一个方法判断 （1.str == ""  2.str == String.Empty  3.str.Length == 0）

static void Main()

        {             string str = "csdn";             System.Diagnostics.Stopwatch st = new System.Diagnostics.Stopwatch();             st.Start();             for (int i = 0; i < 100000000; i++)             {                 if (str == "")                 { }             }             st.Stop();             Console.WriteLine("str == '' : " + st.ElapsedMilliseconds);             st = new System.Diagnostics.Stopwatch();             st.Start();             for (int i = 0; i < 100000000; i++)             {                 if (str == String.Empty)                 { }             }             st.Stop();             Console.WriteLine("str == String.Empty : " + st.ElapsedMilliseconds);             st = new System.Diagnostics.Stopwatch();             st.Start();             for (int i = 0; i < 100000000; i++)             {                 if (str.Length == 0)                 { }             }             st.Stop();             Console.WriteLine("str.Length == 0 : " + st.ElapsedMilliseconds);             Console.ReadKey();         }

F5 用行 str == '': 1951  (微妙为单位) str =='': 1867 str =='': 522