为什么我们使用的主要方法或内部类

为什么我们使用的是"使用"在类或函数的关键字，而"使用"关键字使用之前声明一个类。

像这样的

using System;

using System.IO;

using System.Text;

 

class MemStream

{

    static void Main()

    {

        int count;

        byte[] byteArray;

        char[] charArray;

        UnicodeEncoding uniEncoding = new UnicodeEncoding();

 

        // Create the data to write to the stream.

        byte[] firstString = uniEncoding.GetBytes(

            "Invalid file path characters are: ");

        byte[] secondString = uniEncoding.GetBytes(

            Path.GetInvalidPathChars());

 

        using(MemoryStream memStream = new MemoryStream(100))

        {

            // Write the first string to the stream.

            memStream.Write(firstString, 0 , firstString.Length);

 

            // Write the second string to the stream, byte by byte.

            count = 0;

            while(count < secondString.Length)

            {

                memStream.WriteByte(secondString[count++]);

            }

 

            // Write the stream properties to the console.

            Console.WriteLine(

                "Capacity = {0}, Length = {1}, Position = {2}\n",

                memStream.Capacity.ToString(),

                memStream.Length.ToString(),

                memStream.Position.ToString());

 

            // Set the position to the beginning of the stream.

            memStream.Seek(0, SeekOrigin.Begin);

 

            // Read the first 20 bytes from the stream.

            byteArray = new byte[memStream.Length];

            count = memStream.Read(byteArray, 0, 20);

 

            // Read the remaining bytes, byte by byte.

            while(count < memStream.Length)

            {

                byteArray[count++] =

                    Convert.ToByte(memStream.ReadByte());

            }

 

            // Decode the byte array into a char array

            // and write it to the console.

            charArray = new char[uniEncoding.GetCharCount(

                byteArray, 0, count)];

            uniEncoding.GetDecoder().GetChars(

                byteArray, 0, count, charArray, 0);

            Console.WriteLine(charArray);

        }

    }

}

 

 using(MemoryStream memStream = new MemoryStream(100))