.NET(C#)：中StringBuilder, List, MemoryStream 容量（Capacity屬性）的變化

今天看了一道微軟認證MCTS的樣題，考的是StringBuilder容量（Capacity屬性）的變化，暈……連這種題都有啊，呵呵，不過挺有意思的，為此我研究了一下一些常見的有Capacity屬性的容器，也就是題目上說的那三個，另外還有個ArrayList，不過它和List<T>工作原理一樣，就沒把他放在標題上。

 

  下面是我的電腦測試結果：

（32位，WinXP SP2家庭版，.NET Framework 3.5 SP1）

StringBuilder

16 32 64 128 256 512 1024

List<T>

0 4 8 16 32 64 128 256 512 1024

ArrayList

0 4 8 16 32 64 128 256 512 1024

MemoryStream

0 256 512 1024

 

 

 

 測試代碼

using System;

using System.Text;

using System.Collections.Generic;

using System.Reflection;

 

namespace Mgen.TTC

{

    class Program

    {

        static int count = 1000;

        static void Main()

        {

            test(typeof(StringBuilder), "Append", 'c');

            test(typeof(List<int>), "Add", 1);

            test(typeof(System.Collections.ArrayList), "Add", 2);

            test(typeof(System.IO.MemoryStream), "WriteByte", (byte)3);

        }

 

        static void test(Type type, string addMethod, object addObj)

        {

            var instance = Activator.CreateInstance(type);

            Console.Write("{0}: ", type.Name);

            int capacity = GetCapacity(instance);

            Console.Write(" {0}", capacity);

            for (int i = 0; i < count; i++)

            {

                CallAdd(instance, addMethod, addObj);

                int chk = GetCapacity(instance);

                if (chk != capacity)

                    Console.Write(" {0}", capacity = chk);

 

            }

            Console.WriteLine();

        }

 

        static void CallAdd(object instance, string method, object arg)

        {

            instance.GetType().GetMethod(method, new Type[] { arg.GetType() }).Invoke(instance, new object[] { arg });

        }

 

        static int GetCapacity(object obj)

        {

            return (int)obj.GetType().GetProperty("Capacity").GetValue(obj, null);

 

        }

    }

}