这些情况使用StringBuilder代替String（抄袭加翻译）_dont concatenate string in loop,use stringbuilder -优快云博客

本文探讨了String与StringBuilder在.NET中的不同之处，包括它们的可变性、内存分配方式及应用场景等。介绍了如何根据不同的需求选择合适的类型以提高程序效率。

String和StringBuilder的不同：

It belongs to String namespace	It belongs to String. Text namespace
String object is immutable	StringBuilder object is mutable
Assigning: String s= "something important";	Assigning: StringBuilder sbuild= new StringBuilder("something important");
We can use '+' operator or Concat method to concatenate the strings.	Here we are using Append method.
When string concatenation happens, additional memory will be allocated.	Here additional memory will be allocated when the string buffer capacity exceeds only.

对于时间关键的程序在以下情况使用StringBuilder代替String:

If the number of appends is unknown. （要连接的字符串数量不知道）
If appending is on string variables instead of string literals. （连接的是String对象而不是字符串）
If string concatenation is in loops. （字符串的连接在循环中）
Concatenating string objects returned by multiple methods.（连接被多个方法返回的String对象）

(from :http://www.c-sharpcorner.com/UploadFile/satisharveti/codeperpart108252009063227AM/codeperpart1.aspx)

（from: http://www.c-sharpcorner.com/UploadFile/jitendra1987/4169/）

static void Main(string[] args) { DateTime dt = DateTime.Now; string testString = ""; for (int i = 0; i < 10000; i++) { testString += "test"; } Console.WriteLine("String Performance Test: " + Math.Round(DateTime.Now.Subtract(dt).TotalSeconds,2) + " Seconds : " + Math.Round(DateTime.Now.Subtract(dt).TotalMilliseconds,2) + " Milliseconds"); dt = DateTime.Now; StringBuilder testSBuilder = new StringBuilder(); for (int i = 0; i < 10000; i++) { testSBuilder.Append("test"); } Console.WriteLine("StringBuilder Performance Test: " + Math.Round(DateTime.Now.Subtract(dt).TotalSeconds,2) + " Seconds : " + Math.Round(DateTime.Now.Subtract(dt).TotalMilliseconds,2) + " Milliseconds"); Console.ReadLine(); }