Servers in java

Hey,

i am using the HeadFirst java book to study java. There is a simple program to
teach about sockets. There is two classes in the program. A client and a server.

When the client connects to the server, the server sends back a message.
here is the code for the classes. its straight from the book

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();
    }
}

and the server

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

public class DailyAdviceServer1
{
    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)
    {
        DailyAdviceServer1 server = new DailyAdviceServer1();
        server.go();
    }

}

The code works just fine if i run the server and then run the client on my own
pc. I tried entering my pc's ip address instead of 127.0.0.1 (which the book says is localhost) and got my friend to run to client on his own pc elsewhere.

Nothing happened!

What would i need to get this program to run on seperate machines? Is there alot more code to be done??