I think you need to fully qualify the class name with it's package name.
Try changing
CREATE PROCEDURE GetAllSeatS(OUT sid varchar(5), out loc varchar(15), OUT ext char(4))
PARAMETER STYLE JAVA READS SQL DATA LANGUAGE JAVA EXTERNAL NAME
'WorkPlace_Seat_Allocation.View_All_Seats';
to
CREATE PROCEDURE GetAllSeatS(OUT sid varchar(5), out loc varchar(15), OUT ext char(4))
PARAMETER STYLE JAVA READS SQL DATA LANGUAGE JAVA EXTERNAL NAME
'workplace_seat_allocation.WorkPlace_Seat_Allocation.View_All_Seats';
Hope this helps,
Fredrik