Worksheet

Hi.
Am getting unable to resolve error class for worksheet.I need to fecth multiple sheets in one scripts.

The scripts on which am getting error is as follows
Workbook worksheet = Workbook.getWorksheets(workbook);

for (int i = 0; i < worksheet.size(); i++)
{
Worksheet worksheet = (Worksheet)worksheet.get(i);
//some actions....
higlighted part is wr am getting error......should there b any jar files to be added for using worksheets.