将程序中的ascii码改为16进制应该怎么该！求指导

try
{

            // Translate the passed message into ASCII and store it as a Byte array.
            Byte[] data = System.Text.Encoding.ASCII.GetBytes(message);
            // Get a client stream for reading and writing.
            //  Stream stream = client.GetStream();

            NetworkStream stream = client.GetStream();

            // Send the message to the connected TcpServer. 
            stream.Write(data, 0, data.Length);

            Console.WriteLine("Sent: {0}", message);

            // Receive the TcpServer.response.

            // Buffer to store the response bytes.
            data = new Byte[256];

            // String to store the response ASCII representation.
            String responseData = String.Empty;

            // Read the first batch of the TcpServer response bytes.
            Int32 bytes = stream.Read(data, 0, data.Length);
            responseData = System.Text.Encoding.ASCII.GetString(data, 0, bytes);
            return responseData;
            //Console.WriteLine("Received: {0}", responseData);

            // Close everything.
            stream.Close();

        }
        catch (ArgumentNullException e)
        {

public class TestAscii {

public static void main(String[] s){
printAsciiHex('a');
printAsciiHex('1');

printHex(1);
printHex(16);
printHex(18);
printHex(255);
}

public static void printAsciiHex(char ch){
int i=(int)ch; //i=a的ASCII
System.out.println(ch + " ascii:" + i);

String str=Integer.toString(i,16); //十六进制
System.out.println(ch + " ascii 的十六进制:" + str);
}

//得到一个数的十六进制形式
public static void printHex(int i){
String str=Integer.toString(i,16); //十六进制
System.out.println(i + "的十六进制:" + str);
}
}

 public class StringToHex{

      public String convertStringToHex(String str){

      char[] chars = str.toCharArray();

      StringBuffer hex = new StringBuffer();
      for(int i = 0; i < chars.length; i++){
        hex.append(Integer.toHexString((int)chars[i]));
      }

      return hex.toString();
      }

      public String convertHexToString(String hex){

      StringBuilder sb = new StringBuilder();
      StringBuilder temp = new StringBuilder();

      //49204c6f7665204a617661 split into two characters 49, 20, 4c...
      for( int i=0; i<hex.length()-1; i+=2 ){

          //grab the hex in pairs
          String output = hex.substring(i, (i + 2));
          //convert hex to decimal
          int decimal = Integer.parseInt(output, 16);
          //convert the decimal to character
          sb.append((char)decimal);

          temp.append(decimal);
      }

      return sb.toString();
      }

      //504F533838383834  POS88884
      public static void main(String[] args) {

      StringToHex strToHex = new StringToHex();
      System.out.println("\n-----ASCII码转换为16进制 -----");
      String str = "POS88884"; 
      System.out.println("字符串: " + str);
      String hex = strToHex.convertStringToHex(str);
      System.out.println("转换为16进制 : " + hex);

      System.out.println("\n***** 16进制转换为ASCII *****");
      System.out.println("Hex : " + hex);
      System.out.println("ASCII : " + strToHex.convertHexToString(hex));
      }
    }