SUM with condition in ireport 4.0

Im using ireport I finish the report but I need to do a SUM with condition dunno how to that im been searching but no result

I guess this if statement would be right one but I dunno how to use

If ($f{pallet}==''){

/*SUM IN VAR BUNDLES */

}else {

/*SUM IN VAR PALLET*/

}

this my details of the ireport

 ----------------------
|pallet|bundles| cant  |
|------|-------|-------- 
|  1   |       |  1000 |
|  2   |       |  2000 |
|      |   1   |  3000 |
|      |   2   |  1000 |
|  3   |       |  1000 |
|------|-------|-------|

I would like something like this.

/* FOOTER */

---------------------------------------------------------
|Total PALLET:3000|TOTAL BUNDLES:4000| TOTAL UNIT:8000  |
|-----------------|------------------|------------------|