常用类库StringBuilder

1.使用StringBuilder拼接字符串实例：

string[] lines = File.ReadAllLines("sdjk.txt", Encoding.Default);

        //创建监视对象

Stopwatch watch = new Stopwatch();

StringBuilder str = new StringBuilder();

//监视开始

watch.Start();

for (int i = 0; i < lines.Length; i++)

{

str.Append(lines[i]);

}

//监视结束

watch.Stop();

//显示监视时间

Console.WriteLine(watch.Elapsed);