怎么在android中利用Socket实现一个聊天小程序

package org.hwq.echo;  import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.io.PrintWriter; import java.net.ServerSocket; import java.net.Socket;  public class TalkServer {   public static void main(String[] args) throws IOException{     ServerSocket server = null;     Socket client = null;     BufferedReader in = null;     PrintWriter out = null;     try{       server = new ServerSocket(4700);       client = server.accept();       out = new PrintWriter(client.getOutputStream());       in = new BufferedReader(new InputStreamReader(client.getInputStream()));       String line = in.readLine();       while(!"bye".equals(line)){         System.out.println("client:"+line);         out.println("echo:"+line);         out.flush();         line = in.readLine();       }     }catch (Exception e) {       e.printStackTrace();       if(client !=null)         client.close();       if(server != null)         server.close();     }   } }