how to write a custom prompt for begin and end date parameters

I created a begin date parameter setting my default value expression as

new net.sf.jasperreports.types.date.DateRangeBuilder("MONTH-1").toDateRange()

and an end date parameter setting the default value expression as

new net.sf.jasperreports.types.date.DateRangeBuilder("DAY").toDateRange()

The parameters have "MONTH-1" and "DAY" in the fields that are to be entered. How can I set my own custom writing/message for the field?