关于 string和StringBuilder的区别参考MSDN。本文用程序演示它们在内存中的区别,及其因此其行为不同。
//Demo string memory model
namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
        {
string a = "1234";
string b = a;//a,and b point to the same address
Console.WriteLine(a);
Console.WriteLine(b);
a = "5678";
Console.WriteLine(a);
Console.WriteLine(b);//That b's value is not changed means string's value cann't be changed
            Console.ReadKey();
        } 
            
    }
}
output:
1234
1234
5678;change a's value,b's value is not changed
1234
//Demo StringBuilder's memory model
namespace ConsoleApplication3
{
    class Program
    {
        static void Main(string[] args)
        {
  
            StringBuilder a = new StringBuilder("1234");
            StringBuilder b = new StringBuilder();
            b = a;
            a.Clear();
            a.Append("5678");
            Console.WriteLine(a);
            Console.WriteLine(b);
            Console.ReadKey();
        }
        
    }
}
output:
5678
5678