Java Reference
In-Depth Information
CHALLENGE 13.3
Complete the class diagram in Figure 13.3 to show a refactored
Substance
class
and a new, immutable
Chemical_1
class. Include a
getMoles()
method in
the
Chemical_1
class, so that classes other than
Substance
can check
a chemical batch's molality.
Figure 13.3. Complete this diagram to extract the immutable aspects of
Substance
into the
Chemical_1
class.
Sharing Flyweights
Extracting the immutable part of an object is half the battle in applying the F
LYWEIGHT
pattern. The remaining work includes creating a flyweight factory that instantiates flyweights
and that arranges for clients to share them. You also have to ensure that clients will use your
factory instead of constructing instances of the flyweight class themselves.
To make chemicals flyweights, you need a factory, perhaps a
ChemicalFactory_1
class,
with a static method that returns a chemical given its name. You might store chemicals in
a hash map, creating known chemicals as part of the factory's initialization. Figure 13.4 shows
a design for a
ChemicalFactory_1
. The code for
ChemicalFactory_1
can use a static
initializer to store
Chemical_1
objects in a hash map:
