StringBuild

* StringBuild 初始容量是 32
* 1、属性：
* Length:现有内容长度；
* Capacity：StringBuild当前最大容量
*
* 2、
* 通过 设置Length=10,可以自动裁剪字符串，若原本不足10个时，用空格代替

                //1、默认容量（默认 最大容量=32）
                StringBuilder buffer = new StringBuilder();               
                Console.WriteLine(string.Format("StringBuild的Length={0}，Capacity={1}",buffer.Length,buffer.Capacity));

                //2、自动分配最大容量(2倍原则)
                buffer.Append("Hello,how are you?Hello,how are you?");
                Console.WriteLine(string.Format("StringBuild的Length={0}，Capacity={1}", buffer.Length, buffer.Capacity));


                //3、手动分配 最大容量；
                buffer.Capacity = 100;
                Console.WriteLine(string.Format("StringBuild的Length={0}，Capacity={1}", buffer.Length, buffer.Capacity));

                //4、通过Length截取字符串
                buffer.Length = 10;
                Console.WriteLine(string.Format("StringBuild的Length={0}，Capacity={1}", buffer.Length, buffer.Capacity));