Supermarket operation support system - Software Development Case Studies in Java - page 368

public double getPrice( long code){
Item it # dbm.getItem(code);
if (it ## null ) return -1;
return it.price;
}
public long startTransaction( long customer,
long employee)
throws Exception {
return dbm.startTransaction(customer, employee);
}
public void buy( long item, long quantity,
long transaction)
throws Exception {
dbm.buy(item,quantity,transaction);
}
public void endTransaction( long transaction)
throws Exception {
dbm.closeTransaction(transaction);
}
}
The interface DBManager defines the operations offered by a database. It
is similar to the Market interface but is more data oriented.
package MarketDB;
public interface DBManager {
// return information about an employee
Employee getEmployee( long code);
// return information about a customer
Customer getCustomer( long code);
// return information about a product
Item getItem( long code);
// start a new transaction and return its code
long startTransaction( long customer, long employee)
throws Exception;
// record the acquisition of a product
// in a transaction
void buy( long item, long quantity, long transaction)
throws Exception;
// close a transaction
void endTransaction( long code) throws Exception;
}
The information stored in the database is handled through four data
classes: Item , Customer , Employee , Transaction . These classes hold information
in public attributes.
package MarketDB;
public class Item {