Hash Table Extract

Question

Hi,
I'm hoping that someone will be able to explain how I extract the first element (in this case the name) from the hashtable in the server code below (case N:).
import java.net.*;
import java.io.*;
import java.util.*;
public class Server{
  private PrintWriter pw;
  private BufferedReader bf;
  private ServerSocket ss;
  private Socket s;
  //Hashtable used to store test data
  //Set up hash table with test data
  private Hashtable emails;
  public Server() throws Exception{
    emails = new Hashtable();
    emails.put("Ince","[email protected]");
    emails.put("Roberts","[email protected]");
    emails.put("Timms","[email protected]");
    emails.put("Rowlands","[email protected]");
    emails.put("Eustace","[email protected]");
    emails.put("Lord","[email protected]");
      System.out.println("...Setting up server socket");
      ss = new ServerSocket(1200);
      System.out.println("..waiting for connection ");
      s = ss.accept();
      System.out.println("..connection made");
      InputStream is = s.getInputStream();
      bf = new BufferedReader(new InputStreamReader(is));
      OutputStream os = s.getOutputStream();
      pw = new PrintWriter(os, true);
    public void  Run() throws Exception
    boolean cont = true;
    while(cont == true)//server runs while true
      String clientLine = bf.readLine();
      System.out.println( clientLine ); //used to check the connection
      switch(clientLine.charAt(0))
      case'E':
        String Name = "";
        String staffName = null;
        Name = clientLine.substring(1,clientLine.length());
        staffName = (String) emails.get(Name);
        pw.println(staffName);
        break;
      case'N':
        String email = "";
        String emailAddress = null;
        email = clientLine.substring(1,clientLine.length());
        emailAddress = (String) emails.get(email);
        pw.println(emailAddress);
        break;
      case'U':
        String number = (String) emails.get(clientLine);
        if(number == null)
        pw.println(number);
        break;
      case'Q':
        pw.close();
        bf.close();
        s.close();
        cont = false;
      break;
    public static void main(String[]args) throws Exception{
      Server serv = new Server();
      serv.Run();
}

Answer 1

1) Use HashMap if possible, rather than Hashtable.
2) HashMap and Hashtable don't have a "first" element. You can call entrySet(), keySet(), or values() and get the first element from the resulting collection's iteration, but that could be any element from the map--first added, last added, middle. It has no relation to the order added or to any sorting.
If you want to retrieve in the order added, use LinkeHashMap.
If you want to retrieve in a sorted order, use a SortedMap, such as TreeMap.
Make sure you implement equals and hashCode correctly, and if you want to sort, implement Comparable or provide a Comparator.
http://developer.java.sun.com/developer/Books/effectivejava/Chapter3.pdf
Making Java Objects Comparable
http://java.sun.com/docs/books/tutorial/collections/interfaces/order.html
http://www.javaworld.com/javaworld/jw-12-2002/jw-1227-sort.html