DDF- How to write excel sheet while executing test case

I am using exact same framework from Module 20. Its working perfect at my workplace. While executing test case I am capturing actual results from application and storing in to string example..final amount and interest rate . I have two columns in excel sheet to write it back.
there are 200 testcases same workflow with different set of data.
Do I need create again xls object for each and every testcase to write in to xls sheet or is there any way I can write in to excel.
Can you please explain how write it back.

With Regards
Sankara