请帮忙解释以下这个方法的意思？

import java.io.*;
import java.net.*;public class JabberServer {  
  public static final int PORT = 10000;
  public static void main(String[] args) 
      throws IOException {
                  ServerSocket s = new ServerSocket(PORT);
                  System.out.println("Started: " + s);
               try {
                       Socket socket = s.accept();
                      
                         try {
                                System.out.println("Connection accepted: "+ socket);
                                BufferedReader in = new BufferedReader(
                                                  new InputStreamReader(
                                                   socket.getInputStream()
                                                                       )
                                            );                                PrintWriter out = new PrintWriter(
                                                  new BufferedWriter(
                                                  new OutputStreamWriter(
                                                    socket.getOutputStream()
                                                                        )
                                                                     )
                                                            ,true);
                       while (true) {  
                        String str = in.readLine();   //  这句什么意思？
                           if (str.equals("END"))
                             break;
                           System.out.println("Echoing: " + str);
                                out.println(str);    //  这句什么意思？
                            }
                           
                            } 
                            finally {
                              System.out.println("closing...");
                                socket.close();
                                 }
                }
                 finally {
                   s.close();
                         }
                         } 
} 
--------------------------------------------
str = in.readLine();   //  这句什么意思？
 out.println(str);    //  这句什么意思？这两个在这里分别发挥什么作用？