Last time I checked you couldn't use sequence.nextval outside of a SQL statement (even in PL/SQL). You could do a:
select sequence.nextval from dual
to get the value into a Java variable and then bind it in your call. Or you could do as the previous poster suggested and get the nextval in your PL/SQL. If you need the value back in Java, then either return it as an OUT variable or do a:
select sequence.currval from dual
to get it after.