Factory Method

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Factory Method

• By Judith Mziray
• And
• Jerry Cipolla

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Overview

• Big picture view of the Factory Method
• Participants of the Factory Method
• Case study/hypothetical
• Defining or classifying the elements within the
  hypothetical
• Pros and Cons of the Factory Method
• Hypothetical applied to a diagram/structure
• Questions ??

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Factory Method Big Picture

• Creates or manufactures objects, just like a real
  factory.
• The factory method is used when its just not
  possible for a CLASS to predict what CLASS of
  OBJECTS will be needed and what exact
  INSTANTIATION or action is needed.
• Class DELEGATES to a SUBCLASS which picks the
  appropriate object to instantiate, given the
  specific circumstances.

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Participants

• Product defines the interface of objects the
  factory method creates
• ConcreteProduct implements the Product
  interface
• Creator declares the factory method, which
  returns an object of type Product
• ConcreteCreator overrides the factory method to
  return an instance of a ConcreteProduct

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Factory Method- getting rid of the beauracracy

• Hypothetical Imagine you are a special forces
  soldier in a far off country. Intelligence and
  the politicians know something is going to happen
  within the operation. However, what specifically
  needs to happen must be decided on a split second
  decision. You can shoot your gun, you can shoot
  your bazooka, or you can throw a grenade. It
  just depends on what the enemy is doing, which
  cannot be predicted.

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Hypothetical continued

• Intelligence and the politicians must rely on
  your judgment.
• Look at it this way, intelligence and the
  politicians are the classes, and you, the special
  forces soldier in the field, are the creator.
  Intelligence has delegated to you to pick the
  appropriate subclass that will instantiate the
  correct object. In other words, you pick the
  subclass to make the correct instantiation such
  as a gun that will shoot, a grenade and pull the
  pin, or a bazooka to shoot.

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Hypothetical defined

• Class - Politicians delegating authority down
  the line
• Class - Intelligence delegating authority to
  you
• Delegating Subclass/Creator You, the special
  forces soldier, are the delegating subclass or
  creator that chooses which object to pick, the
  gun, the grenade, or the bazooka, which all will
  be instantiated.

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Object and Instantiation

• Gun (object) -- shoot (instantiation)
• Grenade (object) - pull the pin (instantiation)
• Bazooka (object) shoot (instantiation)

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Pros and Cons -Factory Method

• Lets a class defer instantiation to subclasses
• Eliminates the need to bind application-specific
  classes into your code
• Disadvantage is sub-classing may become too
  complex or tedious for the client in later
  additions to the code.

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Structure
instantiation
class
Intelligence Politicians
Pull pin
Special forces (YOU)
Grenade
Sub-class
object
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Questions ?????