class ISBNFocusListener extends FocusAdapter
{
    public void focusLost(FocusEvent e)
    {
        if(!Dao.selectBookInfo(ISBN.getText().trim()).isEmpty());
        {
            JOptionPane.showMessageDialog(null,"添加书号重复");
            return;                
        }
    }
}                                                                          错误  错误 错误
public static int Insertbook(String ISBN,String typeid,String 
        bookname,String writer,String translator,String publisher,Date date,Double price)
{
    int i=0;
    try
    {
        String sql="insert into bookinfo(ISBN,typeid,bookname,writer,translator,"+
          "publisher,date,price)values('"+ISBN+"','"+typeid+"','"+bookname+"','"+writer+"'," +
                  "'"+translator+"'," +
                  "'"+publisher+"','"+date+"','"+price+"')";
                  i=Dao.executeUpdate(sql);                                        //执行插入操作
    }
    catch(Exception e)
    {
        System.out.println(e.getMessage());
    }
    Dao.close();                                                                //关闭连接对象
    return i;                                                                    //返回更新记录数
}                            错误  错误 错误