Matching types

Does anybody know how to get BigDecimal from numeric and how to put
BigDecimal to numeric using jdbc?
The first thing seems to work automaticaly.
BigDecimal seems to be converted into double precision when put in a
query. Then it can't be compared with a numeric value.

ERROR:  Unable to identify an operator '=' for types 'numeric' and
'double precision'
  You will have to retype this query using an explicit cast

Can it be done without doing an explicit cast?

Thanks in advance.