String PK StringBuilder,传说就是传说，只有动手实验，才能得出确定的答案

本机测试结果如下：

大部分情况下，string 性能并不比StringBuilder差，只有特殊情况才出现差异，并非 如前面有些朋友测试的结果哪样，只要使用StringBuilder 就一定比String表现优异。

另外，大多数测试者都没有考虑内存分配的时间与成本（因为大多数的内存都比较在>2G)。

本次测试也只考虑 时间运行 效率，没有考虑空间成本

本次测试条件：.net 4.0  硬件：Tinkpad t540P,4G内存 win8.1

第一种方法：

  1 [TestClass]
  2     public class StringTest1
  3     {
  4         [TestMethod]
  5         public void String1Test1()
  6         {
  7             for (int i = 0; i < 1; i++)
  8             {
  9                 string queryString = @"select p from DALParty as p where p.OwnerID=:OwnerID";
 10                 queryString += " and (p.Name like :Name  or p.Code like :Name or p.TaxCode like :Name)";
 11                 queryString += " order by p.Name ";
 12             }
 13         }
 14         [TestMethod]
 15         public void String10Test1()
 16         {
 17             for (int i = 0; i < 10; i++)
 18             {
 19                 string queryString = @"select p from DALParty as p where p.OwnerID=:OwnerID";
 20                 queryString += " and (p.Name like :Name  or p.Code like :Name or p.TaxCode like :Name)";
 21                 queryString += " order by p.Name ";
 22             }
 23         }
 24         [TestMethod]
 25         public void String100Test1()
 26         {
 27             for (int i = 0; i < 100; i++)
 28             {
 29                 string queryString = @"select p from DALParty as p where p.OwnerID=:OwnerID";
 30                 queryString += " and (p.Name like :Name  or p.Code like :Name or p.TaxCode like :Name)";
 31                 queryString += " order by p.Name ";
 32             }
 33         }
 34         [TestMethod]
 35         public void String1000Test1()
 36         {
 37             for (int i = 0; i < 1000; i++)
 38             {
 39                 string queryString = @"select p from DALParty as p where p.OwnerID=:OwnerID";
 40                 queryString += " and (p.Name like :Name  or p.Code like :Name or p.TaxCode like :Name)";
 41                 queryString += " order by p.Name ";
 42             }
 43         }
 44         [TestMethod]
 45         public void String10000Test1()
 46         {
 47             for (int i = 0; i < 10000; i++)
 48             {
 49                 string queryString = @"select p from DALParty as p where p.OwnerID=:OwnerID";
 50                 queryString += " and (p.Name like :Name  or p.Code like :Name or p.TaxCode like :Name)";
 51                 queryString += " order by p.Name ";
 52             }
 53         }
 54 
 55         [TestMethod]
 56         public void StringBuilder1Test1()
 57         {            
 58             for (int i = 0; i < 1; i++)
 59             {
 60                 StringBuilder ssb = new StringBuilder();
 61                 ssb.Append(@"select p from DALParty as p where p.OwnerID=:OwnerID");
 62                 ssb.Append(" and (p.Name like :Name  or p.Code like :Name or p.TaxCode like :Name)");
 63                 ssb.Append(" order by p.Name ");
 64             }
 65         }
 66         [TestMethod]
 67         public void StringBuilder10Test1()
 68         {
 69             for (int i = 0; i < 10; i++)
 70             {
 71                 StringBuilder ssb = new StringBuilder();
 72                 ssb.Append(@"select p from DALParty as p where p.OwnerID=:OwnerID");
 73                 ssb.Append(" and (p.Name like :Name  or p.Code like :Name or p.TaxCode like :Name)");
 74                 ssb.Append(" order by p.Name ");
 75             }
 76         }
 77         [TestMethod]
 78         public void StringBuilder100Test1()
 79         {
 80             for (int i = 0; i < 100; i++)
 81             {
 82                 StringBuilder ssb = new StringBuilder();
 83                 ssb.Append(@"select p from DALParty as p where p.OwnerID=:OwnerID");
 84                 ssb.Append(" and (p.Name like :Name  or p.Code like :Name or p.TaxCode like :Name)");
 85                 ssb.Append(" order by p.Name ");
 86             }
 87         }
 88         [TestMethod]
 89         public void StringBuilder1000Test1()
 90         {
 91             for (int i = 0; i < 1000; i++)
 92             {
 93                 StringBuilder ssb = new StringBuilder();
 94                 ssb.Append(@"select p from DALParty as p where p.OwnerID=:OwnerID");
 95                 ssb.Append(" and (p.Name like :Name  or p.Code like :Name or p.TaxCode like :Name)");
 96                 ssb.Append(" order by p.Name ");
 97             }
 98         }
 99         [TestMethod]
100         public void StringBuilder10000Test1()
101         {
102             for (int i = 0; i < 10000; i++)
103             {
104                 StringBuilder ssb = new StringBuilder();
105                 ssb.Append(@"select p from DALParty as p where p.OwnerID=:OwnerID");
106                 ssb.Append(" and (p.Name like :Name  or p.Code like :Name or p.TaxCode like :Name)");
107                 ssb.Append(" order by p.Name ");
108             }
109         }
110     }

第二种方法

  1 [TestClass]
  2     public class StringTest2
  3     {
  4         [TestMethod]
  5         public void String1Test2()
  6         {
  7             string queryString = string.Empty;
  8             for (int i = 0; i < 1; i++)
  9             {
 10                 queryString = string.Empty;
 11                 queryString = @"select p from DALParty as p where p.OwnerID=:OwnerID";
 12                 queryString += " and (p.Name like :Name  or p.Code like :Name or p.TaxCode like :Name)";
 13                 queryString += " order by p.Name ";
 14             }
 15         }
 16         [TestMethod]
 17         public void String10Test2()
 18         {
 19             string queryString = string.Empty;
 20             for (int i = 0; i < 10; i++)
 21             {
 22                 queryString = string.Empty;
 23                 queryString = @"select p from DALParty as p where p.OwnerID=:OwnerID";
 24                 queryString += " and (p.Name like :Name  or p.Code like :Name or p.TaxCode like :Name)";
 25                 queryString += " order by p.Name ";
 26             }
 27         }
 28         [TestMethod]
 29         public void String100Test2()
 30         {
 31             string queryString = string.Empty;
 32             for (int i = 0; i < 100; i++)
 33             {
 34                 queryString = string.Empty;
 35                 queryString = @"select p from DALParty as p where p.OwnerID=:OwnerID";
 36                 queryString += " and (p.Name like :Name  or p.Code like :Name or p.TaxCode like :Name)";
 37                 queryString += " order by p.Name ";
 38             }
 39         }
 40         [TestMethod]
 41         public void String1000Test2()
 42         {
 43             string queryString = string.Empty;
 44             for (int i = 0; i < 1000; i++)
 45             {
 46                 queryString = string.Empty;
 47                 queryString = @"select p from DALParty as p where p.OwnerID=:OwnerID";
 48                 queryString += " and (p.Name like :Name  or p.Code like :Name or p.TaxCode like :Name)";
 49                 queryString += " order by p.Name ";
 50             }
 51         }
 52         [TestMethod]
 53         public void String10000Test2()
 54         {
 55             string queryString = string.Empty;
 56             for (int i = 0; i < 10000; i++)
 57             {
 58                 queryString = string.Empty;
 59                 queryString = @"select p from DALParty as p where p.OwnerID=:OwnerID";
 60                 queryString += " and (p.Name like :Name  or p.Code like :Name or p.TaxCode like :Name)";
 61                 queryString += " order by p.Name ";
 62             }
 63         }
 64 
 65         [TestMethod]
 66         public void StringBuilder1Test2()
 67         {
 68             StringBuilder ssb = new StringBuilder();
 69             for (int i = 0; i < 1; i++)
 70             {
 71                 ssb.Clear();
 72                 ssb.Append(@"select p from DALParty as p where p.OwnerID=:OwnerID");
 73                 ssb.Append(" and (p.Name like :Name  or p.Code like :Name or p.TaxCode like :Name)");
 74                 ssb.Append(" order by p.Name ");
 75             }
 76         }
 77         [TestMethod]
 78         public void StringBuilder10Test2()
 79         {
 80             StringBuilder ssb = new StringBuilder();
 81             for (int i = 0; i < 10; i++)
 82             {
 83                 ssb.Clear();
 84                 ssb.Append(@"select p from DALParty as p where p.OwnerID=:OwnerID");
 85                 ssb.Append(" and (p.Name like :Name  or p.Code like :Name or p.TaxCode like :Name)");
 86                 ssb.Append(" order by p.Name ");
 87             }
 88         }
 89         [TestMethod]
 90         public void StringBuilder100Test2()
 91         {
 92             StringBuilder ssb = new StringBuilder();
 93             for (int i = 0; i < 100; i++)
 94             {
 95                 ssb.Clear();
 96                 ssb.Append(@"select p from DALParty as p where p.OwnerID=:OwnerID");
 97                 ssb.Append(" and (p.Name like :Name  or p.Code like :Name or p.TaxCode like :Name)");
 98                 ssb.Append(" order by p.Name ");
 99             }
100         }
101         [TestMethod]
102         public void StringBuilder1000Test2()
103         {
104             StringBuilder ssb = new StringBuilder();
105             for (int i = 0; i < 1000; i++)
106             {
107                 ssb.Clear();
108                 ssb.Append(@"select p from DALParty as p where p.OwnerID=:OwnerID");
109                 ssb.Append(" and (p.Name like :Name  or p.Code like :Name or p.TaxCode like :Name)");
110                 ssb.Append(" order by p.Name ");
111             }
112         }
113         [TestMethod]
114         public void StringBuilder10000Test2()
115         {
116             StringBuilder ssb = new StringBuilder();
117             for (int i = 0; i < 10000; i++)
118             {
119                 ssb.Clear();
120                 ssb.Append(@"select p from DALParty as p where p.OwnerID=:OwnerID");
121                 ssb.Append(" and (p.Name like :Name  or p.Code like :Name or p.TaxCode like :Name)");
122                 ssb.Append(" order by p.Name ");
123             }
124         }
125     }

测试结果如下：

根据测试结果如下：

 如果 字符串拼接 次数很小 <= 1000次，两者性能几乎没有差别，只有在字符本身长度大，拼接次数很大的情况下，使用StringBuilder才有意义。

 通过第二次方法测试可表明，在循环体内 每次 new StringBuilder 时，是非常耗时的工作，并且new时预分配内存，也是占内存的，有时并没有使用到。

因此：使用string 还是 StringBuilder 还要看使用环境。

在大部分情况下，string 并不会对性能造成损失，使用string 即方便，也经济，仍然是字符串操作的首先。