text_root_username = new JTextField();
       text_root_username.addKeyListener(this);//////
        text_root_password = new JPasswordField();
        text_root_password.addKeyListener(this);

@Override
    public void keyTyped(KeyEvent e) {


          if(text_root_password.getText().length()>=8){
        e.consume();
        }
         if(text_root_username.getText().length()>=8) {
        e.consume();
          }
    }