我在后面加上一点东西后就好啦,我也不知道为什么
DataOutputStream out1=new DataOutputStream(telnet.getOutputStream());
           out1.writeChars("BYE\n");
           out1.flush();
 
 BufferedReader in = new BufferedReader(new InputStreamReader(telnet.getInputStream()));
     PrintWriter out =  new PrintWriter(new BufferedWriter(new OutputStreamWriter(telnet.getOutputStream())), true);
           String  str = in.readLine();
           System.out.println(str);
 out.println("sdfewrw");
 str = in.readLine();
           System.out.println(str);
 out.println("BYE");
 
 str = in.readLine();
           System.out.println(str);