java - 如何获得表中两列的乘积？

Question

我正在使用 Netbeans 开发 GUI 桌面应用程序。我已经对总数做了一个验证，但没有显示结果。请检查编码天气是否有需要更改或是否有错误。当我执行它时，在第 3 列中它显示错误并且没有结果

private void jButton15ActionPerformed(java.awt.event.ActionEvent evt) {                                          
    Connection con;
    Statement stmt;
    try {
      Class.forName("sun.jdbc.odbc.JdbcOdbc");
    } catch (ClassNotFoundException ex) {
        JOptionPane.showMessageDialog(null, ex);
    }
    try {
        con= DriverManager.getConnection("Jdbc:Odbc:food");
        stmt= con.createStatement();

        String st= JcbSub.getSelectedItem().toString();
        String qt= quantity.getText().toString();
        String query;

        Double u_p= (Double) jTable3.getValueAt(row, 1);
        Integer qut= (Integer) jTable3.getValueAt(row, 2);
        Double tot= u_p * qut; //product of column 1 & column 2


        query="select i_price from food where i_name='"+JcbSub.getSelectedItem()+"'";
        ResultSet rs= stmt.executeQuery(query);

        while(rs.next()){
        jTable3.setValueAt(st, row, 0);
        jTable3.setValueAt(rs.getString("i_price"), row, 1); 
        jTable3.setValueAt(qt, row, 2);
        jTable3.setValueAt(tot, row, 3);  //result column

        row ++;
        }

       } catch (SQLException ex) {
        JOptionPane.showMessageDialog(null, ex);
    } 
}

Answer 1

actually the values in column 1 is selected from the database table and and column 2 values are entered manually using jTextField and transferred to column 2

扩展您的 TableModel 并重写 setValueAt() 方法。

只要第 1 列或第 2 列中的值发生变化(并且都包含非空值)，您就应该计算乘积并更新第 3 列。