UnknownHostException when trying to connect to localhost

[Sue Cavanaugh]

I'm a real greenhorn trying to run the DailyAdviceServer with DailyAdviceClient in two separate command windows on my computer. I started the server just fine in one cmd window and tried to run the client in another but got:

C:\sue\java_work\networking_and_threads>java DailyAdviceClient
java.net.UnknownHostException: 127,0,0,1
at java.net.PlainSocketImpl.connect(Unknown Source)
at java.net.SocksSocketImpl.connect(Unknown Source)
at java.net.Socket.connect(Unknown Source)
at java.net.Socket.connect(Unknown Source)
at java.net.Socket.<init>(Unknown Source)
at java.net.Socket.<init>(Unknown Source)
at DailyAdviceClient.go(DailyAdviceClient.java:9)
at DailyAdviceClient.main(DailyAdviceClient.java:25)

Here's all the code (from Head First Java, 2nd Edition):

// ----------------Client---------------------
import java.io.*;
import java.net.*;

public class DailyAdviceClient {

   public void go() {
      try {
         Socket s = new Socket("127,0,0,1", 4242);
         
         InputStreamReader streamReader = new InputStreamReader(s.getInputStream());
         BufferedReader reader = new BufferedReader(streamReader);

         String advice = reader.readLine();
         System.out.println("Today you should: " + advice);

         reader.close();
      } catch(IOException ex) {
          ex.printStackTrace();
      }
   }

   public static void main(String[] args) {
      DailyAdviceClient client = new DailyAdviceClient();
      client.go();
   }
}

// ----------------Server---------------------

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

public class DailyAdviceServer {

   String[] adviceList = {"Take smaller bites", "Go for the tight jeans.  No they do NOT make you look fat.",
      "One word: inappropriate", "Just for today be honest.  Tell your boss what you *really* think.",
      "You might want to rethink that haircut."};


   public void go() {

      try {
         ServerSocket serverSock = new ServerSocket(4242);
    
         while (true) {

            Socket sock = serverSock.accept();

            PrintWriter writer = new PrintWriter(sock.getOutputStream());
            String advice = getAdvice();
            writer.println(advice);
            writer.close();
            System.out.println(advice);
         }  
      } catch(IOException ex) {
          ex.printStackTrace();
      }
   }

   private String getAdvice() {

      int random = (int) (Math.random() * adviceList.length);
      return adviceList[random];
   }


   public static void main(String args[]) {
      DailyAdviceServer server = new DailyAdviceServer();
      server.go();
   }
}

Thanks in advance for your help!
Sue

[Joe Ess]

IPv4 addresses are usually represented in dot-decimal notation (four numbers, each ranging from 0 to 255, separated by dots, e.g. 208.77.188.166). Each part represents 8 bits of the address, and is therefore called an octet.

IP Address

[Sue Cavanaugh]

Thank you so much, Joe. I knew that's how IP addresses are formatted, but read the code
in the book wrong (need glasses) and didn't catch the inconsistency. I made the
change and my client is getting it's advice with no problem now!

Sue