tablesorting for table

I am trying to sort a table using table sorter class and i have followed each and every step from the below link

http://www.sdn.sap.com/irj/servlet/prt/portal/prtroot/com.sap.nw.wpc.runtime.docs/library/web-dynpro-java/_web-dynpro-java/WDJava%20archive/Developing%20with%20Tables%20in%20Web%20Dynpro.pdf

I am getting table output and am able to view sort icon symbols but the sorting is not working when i click on sort symbols.Please help me with the issue.

For comparator am passing null.Does it anyway relate to my issue.

Thanks,

Anusha