java修改数据库代码

try {
    Class.forName("com.mysql.cj.jdbc.Driver");
    Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/mydb", "username", "password");
} catch (ClassNotFoundException | SQLException e) {
    e.printStackTrace();
}

String sql = "UPDATE users SET age = ? WHERE id = ?";
try (PreparedStatement pstmt = conn.prepareStatement(sql)) {
    pstmt.setInt(1, 30);
    pstmt.setInt(2, 1);
    pstmt.executeUpdate();
} catch (SQLException e) {
    e.printStackTrace();
}

conn.setAutoCommit(false);
try {
    String sql1 = "UPDATE users SET balance = balance - 100 WHERE id = 1";
    String sql2 = "UPDATE users SET balance = balance + 100 WHERE id = 2";
    try (PreparedStatement pstmt1 = conn.prepareStatement(sql1);
         PreparedStatement pstmt2 = conn.prepareStatement(sql2)) {
        pstmt1.executeUpdate();
        pstmt2.executeUpdate();
        conn.commit();
    } catch (SQLException e) {
        conn.rollback();
        e.printStackTrace();
    }
} catch (SQLException e) {
    e.printStackTrace();
} finally {
    conn.setAutoCommit(true);
}