java - 执行 SELECT 查询时，PreparedStatement 和 ResultSet 出现问题？

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UPDATE和INSERT查询没有问题，只有SELECT有问题，这里是所有代码:

try {
        String nCard = jTextField1.getText();
        String deprecate = jTextField2.getText();
        DriverManager.registerDriver(new com.mysql.jdbc.Driver());
        String url = "jdbc:mysql://localhost:3306/visits";
        Connection conn1 = DriverManager.getConnection(url, "root", "");

        PreparedStatement pstmt = conn1.prepareStatement("INSERT INTO `visits`.`transaction` (`numbercard`, `deprecate`) VALUES (?, ?)");
        pstmt.setString(1, nCard);
        pstmt.setString(2, deprecate);
        pstmt.executeUpdate();

        DrawTable();

        PreparedStatement pstmt1 = conn1.prepareStatement("SELECT `balance` FROM `visitor` WHERE `cardID`=?");
        int nCardInt = Integer.parseInt(nCard);
        pstmt1.setInt(1, nCardInt);
        ResultSet rs1 = pstmt1.executeQuery();
        int tempBonus=rs1.getInt(1);
        tempBonus-=Integer.parseInt(deprecate);
        String bonusString = String.valueOf(tempBonus);

        PreparedStatement pstmt2 = conn1.prepareStatement("UPDATE `visitor` SET `balance`=? WHERE cardID=?");
        pstmt2.setString(1, bonusString);
        pstmt2.setString(2, nCard);
        pstmt2.executeUpdate();
    } catch (SQLException ex) {
        Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
    }

我只需要 1 个 ID 单元格即可对其进行操作，“SELECT balance FROM visitor WHERE cardID =？”。如果有人提出更简单的方法，我将非常感激。

Answer 1

您忘记调用 next() ，这会将光标前进到第一行(如果存在)。

A ResultSet cursor is initially positioned before the first row; the first call to the method next makes the first row the current row; the second call makes the second row the current row, and so on.

if (rs1.next())
{
    int tempBonus=rs1.getInt(1);
}