Java.net.UnkownHostException：mailHost

Question

这个教科书示例给了我一个UnknownHostException。我将我的电子邮件地址作为控制台参数，如下所示：java MailClient ivan.ivanhoe@yahoo.com 有人可以给我一个简短的解释，为什么它不可能，或建议我如何运行/重写应用程序，以便它可以发送邮件。谢谢xx

//MailClient.java
//Tries to send an email to my address : UnknownHostException. Trying to sort it now....

import java.net.*;
import java.io.*;

public class MailClient  {

    public static void main (String[] args)  {

        if (args.length == 0)  {
            System.err.println("Usage : java MailClient email@host.com");
            return;
        }

        try  {
            URL u = new URL ("mailto:" + args[0]);
            URLConnection uc = u.openConnection();
            uc.setDoOutput(true);
            uc.connect();
            OutputStream out = uc.getOutputStream();
            StreamCopier.copy(System.in, out);
            out.close();
        }  catch (IOException e)  {
            System.err.print(e);
        }

    } //end main
}



import java.io.*;

public class StreamCopier  {

    public static void main (String[] args)  {

        try  {
            copy (null, null);
        } catch (IOException e) {
            System.err.println(e);
        }
    }

    public static void copy (InputStream in, OutputStream out) throws IOException  {

        //do not allow other threads to read from the  input or
        //write to the output while copying is taking place.
        synchronized (in)  {
            synchronized (out)  {
                byte [] buffer = new byte [256];
                while (true)   {
                    int bytesRead = in.read(buffer);
                    if (bytesRead == -1) 
                        break;
                    out.write(buffer, 0, bytesRead);
                }
            }
        }
    }  //end copy()

}