Java Reference
In-Depth Information
Figure 23.2. Implementations of the
Advisor
interface provide the strategic
recommend()
operation, relying on off-the-shelf engines.
To provide a strategy for a client, you can pass it a particular implementation of the
Advisor
interface. Interfaces can define only instance methods, so
GroupAdvisor
and
ItemAdvisor
must be instantiated to support the
Advisor
interface. However, only one
such object is ever necessary, and so these classes define publicly accessible singletons.
The advisor classes translate calls to
recommend()
into the interfaces that the underlying
engines require. For example, the
GroupAdvisor
class translates calls to
recommend()
into the
advise()
interface that the
Rel8
engine requires:
public Firework recommend(Customer c)
{
return (Firework) Rel8.advise(c);
}
CHALLENGE 23.1
In addition to S
INGLETON
and S
TRATEGY
, what pattern appears in
the
GroupAdvisor
and
ItemAdvisor
classes?
