ActionScript 3.0 Design Patterns

338 | Chapter 9: Template Method Pattern

Minimalist Example: Abstract Template Method

Even though it may not make a lot of sense to use a Template Method design pattern

when you have only a single subclass, doing so helps reveal the design pattern’s struc-

ture. So, in this minimalist example, you should be able to easily see the underlying

structure used in the Template Method. We don’t need much, just two main classes:

• Abstract class with the algorithm for the template method


• At least one concrete class as a subclass of the abstract class

Look for the operations that will be detailed by the subclasses, and the one opera-

tion that will be constant throughout the subclasses.

Bare Bones Template Method

Examples 9-1 and 9-2 show the two classes we need to get started with this simple

but useful pattern. Save each class using the caption name as the filename.

Figure 9-3. Hollywood principle

Example 9-1. AbstractClass.as

package
{
//Abstract Class
class AbstractClass
{
public final function templateMethod( ):void
{
primitiveA( );
primitiveB( );

Abstract Class

operationA()

operationB()

template method()

operationA()

operationB()

(locked algorithm)

Responsible for order of

operations in algorithm

Tucked inside of

locked algorithm

Concrete Class

operationA()

operationB()

Concrete Class

operationA()

operationB()

Specification of operations, but not algorithm.

Calls from template method, but not subclass