Connie's Convenience Store - About Peter Coad

52 Connie’s Convenience Store Establishing Responsibilities for Problem-Domain Objects
A return line item knows what a sale line item knows, plus:
– return price
– reason code
– sale date
– sale price.
Sounds like a great use of gen-spec. It’s domain-based. Some responsibilities are
the same; some are different.
#67. “Common Attributes” Strategy establishing responsibilities /
what I know (consider and challenge)
• Classes with common attributes?
• If the attributes have the same name and meaning, and if you can find a generalizationspecialization
that makes good sense, then add a generalization class and factor out the
commonality.
#120. “Common Services” Strategy establishing responsibilities /
what I do (consider and challenge)
• Classes with common services?
If the services have the same name and meaning, and if you can find a generalizationspecialization
that makes good sense, then add a generalization class and factor
out whatever commonality you discovered.
If the service name is the same, yet the details of the service are different, then
show the service name in both the generalization and the specialization.
Add a return line item, a specialization of a sale line item (Figure 1–34):
SaleLineItem
quantity
taxStatus
calcSubTotal
ReturnLineItem
salePrice
returnPrice
reasonCode
saleDate
calcSubTotal
1
Figure 1–34: Sale line items and return line items: what’s the same, what’s different.
n
Item