public ClientHandler(String addr, int port) {
        try {
            client_socket = new Socket(addr, port);
            os = new PrintStream(client_socket.getOutputStream());
            is = new DataInputStream(client_socket.getInputStream());
            inputLine = new DataInputStream(new BufferedInputStream(System.in));
        } catch (UnknownHostException e) {
            JOptionPane.showMessageDialog(null, "Cannot find host...", "ERROR",
                    JOptionPane.ERROR_MESSAGE);
        } catch (IOException e) {
            JOptionPane.showMessageDialog(null, "Cannot connect to host...",
                    "ERROR", JOptionPane.ERROR_MESSAGE);
        }
    }