C#:字符串连接(+=)与StringBuilder效率分析

在 C# 或 Java 中&＃xff0c;我们可以使用诸如 StringBuilder, StringBuffer 等方式对大量字符串进行拼接操作。当然&＃xff0c;我们也可以直接使用 字符串连接 (&＃43;&＃61;) 的方式进行拼接操作。但是&＃xff0c;两种主要方式在效率上有何区别呢&＃xff1f;我们是否需要针对这两类方式进行区别场景的使用呢&＃xff1f;针对于此&＃xff0c;我做了如下测试&＃xff0c;以证明两种不同方式连接字符串的效率临界值。&＃xff08;关于Java中StringBuilder和StringBuffer的区别&＃xff0c;可以参阅这篇文章&＃xff09;

测试方法是&＃xff1a;重复连接字符串 “Hello World!” 1次到40次&＃xff0c;在每次连接的过程中都分别采用 String Connection (&＃43;&＃61;) 和 StringBuilder 的 Append()方法进行1000次&＃xff0c;并分别计算出两种方法在这1000次运算过程中的获胜比率。通过多次试验&＃xff0c;得到如下统计&＃xff1a;

第一次&＃xff1a;

第二次&＃xff1a;

第三次&＃xff1a;

多次测试结果显示&＃xff0c;在少于8~9次字符串连接时&＃xff0c;String Connection (&＃43;&＃61;) 的效率要略胜一筹。这个结果与 Alois Kraus 给出的测试结果基本一致。

So, 该啥时候使用 &＃43;&＃61;&＃xff0c;想必大家可以了解了。在叠加次数已知的前提下&＃xff0c;若少于10次&＃xff0c;可以优先考虑 &＃43;&＃61;&＃xff0c;否则请不要犹豫的使用StringBuilder。

* 这里需要注意的是&＃xff0c;StringBuilder 的默认 Capacity 是 16&＃xff0c;当然&＃xff0c;测试结果还没到这个数值&＃xff0c;所以不会在较大程度上受此影响。
internal const int DefaultCapacity &＃61; 16;

相关测试代码如下&＃xff1a;
[csharp]
namespace StringEfficiencyTest
{
#region using directives

using System;
using System.Diagnostics;
using System.IO;
using System.Text;

#endregion using directives

internal class Program
{
private static readonly Stopwatch stopwatch &＃61; new Stopwatch();
private static readonly string resultFilePath &＃61; &＃64;"D:result.txt";

private static void Main()
{
try
{
LogFile("TimestStringConnectionWinRatetStringBuilderWinRate");
const int accuracyCorrection &＃61; 1000;

for (var innerTimes &＃61; 1; innerTimes <&＃61; 40; innerTimes&＃43;&＃43;)
{
var result &＃61; CalculateOnce(innerTimes, accuracyCorrection);
Console.WriteLine("Calculate Times: {0} {1}", innerTimes, result ? string.Empty : "&＃64;&＃64;&＃64;&＃64;&＃64;&＃64;&＃64;&＃64;&＃64;&＃64;&＃64;&＃64;");
}

Console.ReadKey();
}
catch (Exception ex)
{
Console.WriteLine(ex);
}
}

// If stringConnection win return true
private static bool CalculateOnce(int times, int accuracyCorrection)
{
var stringConnectionWinCounter &＃61; 0;
var stringBuilderWinCounter &＃61; 0;
for (var i &＃61; 0; i {
//Console.WriteLine("Stacking fold: " &＃43; times);

stopwatch.Reset();
var stringConnectionUsedTime &＃61; StringConnectionTest(times);
//Console.WriteLine("String Connection: " &＃43; stringConnectionUsedTime);

stopwatch.Reset();
var stringBuilderUsedTime &＃61; StringBuilderTest(times);
//Console.WriteLine("String Builder: " &＃43; stringBuilderUsedTime);

if (stringConnectionUsedTime {
stringConnectionWinCounter&＃43;&＃43;;
}

if (stringConnectionUsedTime > stringBuilderUsedTime)
{
stringBuilderWinCounter&＃43;&＃43;;
}
}

Console.WriteLine("---------------------");
var stringConnectionWinRate &＃61; stringConnectionWinCounter*100.0/
(stringConnectionWinCounter &＃43; stringBuilderWinCounter);
Console.WriteLine("String Connection Win Counter: {0}, rate: {1:0.0000}%.", stringConnectionWinCounter,
stringConnectionWinRate);
var stringBuilderWinRate &＃61; stringBuilderWinCounter*100.0/
(stringConnectionWinCounter &＃43; stringBuilderWinCounter);
Console.WriteLine("String Builder Win Counter: {0}, rate: {1:0.0000}%.", stringBuilderWinCounter,
stringBuilderWinRate);

Console.WriteLine("&＃61;&＃61;# {0} win. #&＃61;&＃61;",
stringConnectionWinRate > stringBuilderWinCounter ? "String Connection" : "String Builder");

LogFile(string.Format("{0}t{1}%t{2}%", times, stringConnectionWinRate, stringBuilderWinRate));

return stringConnectionWinCounter > stringBuilderWinCounter;
}

private static long StringConnectionTest(int times)
{
var str &＃61; string.Empty;

stopwatch.Start();

for (var i &＃61; 0; i {
str &＃43;&＃61; "Hello World!";
}

stopwatch.Stop();

return stopwatch.ElapsedTicks;
}

private static long StringBuilderTest(int times)
{
// internal const int DefaultCapacity &＃61; 16;
var str &＃61; new StringBuilder();
//var str &＃61; new StringBuilder(times);

stopwatch.Start();

for (var i &＃61; 0; i {
str.Append("Hello World!");
}

stopwatch.Stop();

return stopwatch.ElapsedTicks;
}

private static void LogFile(string content)
{
using (var fileStream &＃61; File.Open(resultFilePath, FileMode.Append))
{
var writer &＃61; new StreamWriter(fileStream);
writer.WriteLine(content);
writer.Flush();
}
}
}
}
[/csharp]

查看原文&＃xff1a;http://nap7.com/me/stringbuilder-and-stringconnection/