PreparedStatement接口的补充问题——占位符

PreparedStatement接口继承于Statement接口，所以它拥有Statement接口中的方法，详情见
在实际开发中我们在编写SQL语句的时候可能会用到占位符？，它可以代替SQL语句的参数，然后通过setXXX()方法对SQL语句的参数进行赋值。例如

public List<Employee> selectEmp(int firstResult, int pageSize) {
        Connection con = null;
        List<Employee> list = new ArrayList<Employee>();
        try {
            con = DBCon.getCon();
            String sql = "select  * from tb_employee order by id limit ?,?";
            PreparedStatement pstmt = con.prepareStatement(sql);
            pstmt.setInt(1, firstResult);//调用PreparedStatement接口中的setInt方法
            pstmt.setInt(2, pageSize);
            ResultSet rs = pstmt.executeQuery();
            while (rs.next()) {
                Employee emp = new Employee();
                emp.setEmpId(rs.getInt("id"));
                emp.setEmpName(rs.getString("name"));
                emp.setEmpSex(rs.getString("sex"));
                emp.setEmpAge(rs.getInt("age"));
                emp.setTelephoneNo(rs.getString("telephoneNo"));
                emp.setAddress(rs.getString("address"));
                list.add(emp);
            }
            rs.close();
        } catch (Exception ex) {
            ex.printStackTrace();
        } finally {
            try {
                con.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        return list;
    }