import java.io.*;
import java.net.*;
class TextServer
{
public static void main(String argv[])
{
  int port=1000;
  Socket Client;
String msg;
BufferedReader in;
BufferedReader input;
PrintWriter out;
try
{
Client=new Socket("163.net",110);
input=new BufferedReader(new InputStreamReader(System.in));
  in=new BufferedReader(new InputStreamReader(Client.getInputStream()));
out=new PrintWriter(Client.getOutputStream(),true);
System.out.println(in.readLine());
System.out.println("Please Input Your UserName:");
msg=input.readLine();
out.println("USER "+msg);
System.out.println(in.readLine());
System.out.println("Please Input Your Password:");
msg=input.readLine();
out.println("PASS "+msg);
msg=in.readLine();
System.out.println(msg);
out.println("RETR 1");
msg=in.readLine();
         while(msg!="")
        {
System.out.println(msg);
         msg=in.readLine();
         }
}catch(IOException e){System.exit(-1);};

}

}
这是我写的一个程序，想收163邮箱的第一封信件，但是这个循环

         while(msg!="")
        {
System.out.println(msg);
         msg=in.readLine();
         }
总是不能终止，请教高手这是为什么？还有就是我想让输入密码的时候不显示，该怎么写？谢谢！

while(msg!=null)