ActionScript 3.0 Design Patterns.pdf - VideoTutorials-bg.com

Employing Flexibility in the Template Method
Now that you have a better idea of how the Template Method design pattern’s structure
works, let’s see how it can be usefully employed. In this next example, you’ll see
an implementation that uses the same template method for two different concrete
classes. Figure 9-4 shows the class diagram:
WoodShed
doDesign()
determineSupplies()
ShedMaker
templateMethod()
doDesign()
determineSupplies()
storeTools()
doDesign()
determineSupplies()
storeTools()
Figure 9-4. Template method with two concrete classes
SteelShed
doDesign()
determineSupplies()
The main abstract class, ShedMaker, includes three operations in the templateMethod( )
function. Two are abstract and will be overridden by the subclasses where the details
will be supplied. The third operation is a final function, not to be overridden, and will
be used in all subclasses.
The example looks at what you may need in creating a shed in general, and what
different types of sheds may need. The example develops an algorithm that does the
following:
• Designs the shed
• Determines which supplies will be required
• Stores tools in the completed shed
All sheds can use these steps, but depending on the kind of shed, the details will vary
in certain aspects. In this case, we’re supposing that one shed will be made of wood
and the other of corrugated steel. Because designing with wood is different than
designing for steel, the design operation (doDesign( )) is abstract. Likewise, determining
which supplies you need is different as well, and so the determineSupplies( )
function is also abstract. However, no matter what kind of shed is built, storing tools
is the same, and so that function is locked so it won’t be overridden.
To get started, open three new ActionScript files, and enter the code in Examples 9-4
to 9-6. Use the caption names as the filenames, and save all files in the same directory.
Employing Flexibility in the Template Method | 341