当用户单击加入按钮时，应该出现类似“您已经加入此事件”的错误。如何控制它？

模型=（DefaultTableModel）table1.getModel（）; table1是事件总数 model2 =（DefaultTableModel）mytable.getModel（）; mytable是用户的事件

int selected_row=table1.getSelectedRow();*selected row to join*
    String username=User_Login.username.getText();*taking username from user login page to write joinedevent txt*

    if(table1.getRowCount()==0)
    info.setText("There is no event yet !!");
    else
    {
        if(selected_row==-1)
        info.setText("Select a row to join an event !!");
        else
        {

            int event_id=(int) model.getValueAt(selected_row,0);
            String event_name=(String) model.getValueAt(selected_row, 1);
            String event_loc=(String) model.getValueAt(selected_row, 2);
            String date=  (String) model.getValueAt(selected_row, 3);

            UserInfo.joinedEventWriter(username, event_id, event_name, event_loc, date);
            Object [] row_data={event_id,event_name,event_loc,date};
            model2.addRow(row_data);



            info.setText("You joined "+event_name+ " event successfully ## 

            table1.clearSelection();
        }
    }