String.IsNullOrEmpty和"".length>0 那个更高效

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:

01	using System;

02

03	namespace StringNullEmpty

04

{

05	class Program

06

{

07	static void Main( string[] args )

08

{

09	long loop = 100000000;

10	string s = null;

11	long option = 0;

12	long empties1 = 0;

13	long empties2 = 0;

14

15	DateTime time1 = DateTime.Now;

16

17	for (long i = 0; i < loop; i++)

18

{

19	option = i % 4;

20	switch (option)

21

{

22

case 0:

23

s = null;

24

break;

25

case 1:

26	s = String.Empty;

27

break;

28

case 2:

29

s = "H";

30

break;

31

case 3:

32

s = "HI";

33

break;

34

}

35	if (String.IsNullOrEmpty( s ))

36	empties1++;

37

}

38

39	DateTime time2 = DateTime.Now;

40

41	for (long i = 0; i < loop; i++)

42

{

43	option = i % 4;

44	switch (option)

45

{

46

case 0:

47

s = null;

48

break;

49

case 1:

50	s = String.Empty;

51

break;

52

case 2:

53

s = "H";

54

break;

55

case 3:

56

s = "HI";

57

break;

58

}

59	if (s == null || s.Length == 0)

60	empties2++;

61

}

62

63	DateTime time3 = DateTime.Now;

64

65	TimeSpan span1 = time2.Subtract( time1 );

66	TimeSpan span2 = time3.Subtract( time2 );

67	Console.WriteLine( "(String.IsNullOrEmpty( s )): Time={0} Empties={1}",

68	span1, empties1 );

69	Console.WriteLine( "(s == null || s.Length == 0): Time={0} Empties={1}",

70	span2, empties2 );

71	Console.ReadLine();

72

}

73

}

74

}

 一般我喜欢定义成这样：string a=string.Empty;不用判断是否为null。