passing in start/end date results in java exception

[patricia.williams]

My postgres db has a date field and pgadmin query 

    select * from contribution_info where contribution_dt between '2015-01-01' and '2015-12-31'

results in a dt field like "2015-06-15" .  When I try to preview my studio report i get prompts for StartDate and EndDate and I fill those in with 2015-01-01 and 2015-12-31 respectively.  However, I get the java exception then that says net.sf.jasperreports.engine.JRException: java.lang.ClassCastException: java.lang.String cannot be cast to java.util.Date

What am I doing wrong?  Here's the snippet of dataset query that has the date clause 

  and c.contribution_dt between $P{StartDate} and $P{EndDate}

[patricia.williams]

also I setup StartDate and EndDate as java.sql.date 

[patricia.williams]

here's what the server shows on the where clause when I push it over to the server and run it there

    from contribution_info c

    inner join contribution_persent cp on  c.contribution_info_id=cp.contribution_info_id

    inner join persent_info p on cp.persent_info_id=p.persent_info_id

    inner join persent_address pa on p.persent_info_id=pa.persent_info_id

    inner join address_info a on pa.address_info_id=a.address_info_id

   inner join report_info r on c.report_info_id=r.report_info_id

   where 1=1

   and c.contribution_dt between ? and ?

   and (lower(p.name_last) like 'vandergrif' or lower(p.name_organization) like 'vandergrif')