Java resultSet getInt() 无返回值

Question

Here, resultSet.getInt() doesn't work, but I do not know what is wrong with my code.

I want to increment the value of the column (with the name as the variable 'attendance'). Using the SELECT statement I want to read the current value and by using UPDATE I want to increment the corresponding value by 1. But the problem is that int a = r.getInt("'" + attendance + "'"); doesn't work. It always returns the value 0 although the current value isn't 0 (eg 1). What is wrong with my code?

try {
                Class.forName("org.sqlite.JDBC");
                     c = DriverManager.getConnection("jdbc:sqlite:"+ x +".db");
                     s = c.createStatement();
                     r = s.executeQuery("SELECT '" + attendance + "' FROM viewer WHERE name = '" + name + "' AND year = '" + year + "'");
                     while (r.next()){
                         int a = r.getInt("'" + attendance + "'");
                         int b = 1 + a;
                         String sql = "UPDATE viewer SET '" + attendance + "' = ? WHERE name = ? AND year = ? ";
                         p = c.prepareStatement(sql);
                         p.setInt (1,b);
                         p.setString (2,name);
                         p.setInt (3,year);
                         p.executeUpdate();
                     }
                     p.close();
                     c.close();
                     // r.getInt()  value always 0
            }
            catch (ClassNotFoundException | SQLException e) {
                JOptionPane.showMessageDialog(null, e);
            }

Answer 1

since you only have 1 column, you can use column index , instead of column names

int a = r.getInt(0);

Answer 2

Since you wrap the name of the column in single quotes, it is considered as the string literal 'attendance' and not the name of the column which is the value of the variable attendance .
Change to:

"SELECT " + attendance + " FROM viewer WHERE name = '" + name + "' AND year = '" + year + "'"

(why do you concatenate the arguments name and year ? Use placeholders ? just like the UPDATE statement)
and

"UPDATE viewer SET " + attendance + " = ? WHERE name = ? AND year = ? "

and

int a = r.getInt(attendance);