ResultSet rs = stmt.executeQuery(sql); 返回值问题判断

  ResultSet rs = stmt.executeQuery(sql);  //查询返回的结果集
              if(rs.next()==false){    //查不到数据 sql执行false
                     new LoginError().setVisible(true);  
                     this.setVisible(false);
                   }
              
              else  {
              
               String MyID = rs.getString(2);
               String Mypwd  = rs.getString(3);
  
               if(t1.equals(MyID)&&t2.equals(Mypwd)){

                   new ChooseChatTypes().setVisible(true);
                   this.setVisible(false);
                 }
            }