Mid-Level Design Patterns Categories

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Mid-Level Design Patterns Categories
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Objectives

• To propose a classification scheme to help
  remember patterns
• To present the three categories in the scheme

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Topics

• The need for classification
• Pattern categories

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The Need for Classification

• Since their introduction in the mid-1990s,
  hundreds of mid-level design patterns have been
  published.
• How can designers keep them all in mind?
• Many are not that important or have narrow
  application.
• A pattern classification scheme can help
  designers remember many important patterns.

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Pattern Categories

• Broker patterns have a client that needs a
  service from a supplier, and a broker that
  mediates the interaction between client and
  supplier.
• Generator patterns have a client who needs a new
  instance of a product, and a generator class that
  supplies the instance.
• Reactor patterns have a client that needs to
  respond to an event in a target. The client
  delegates this responsibility to a reactor.

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Category Analogies

• Brokers are like stock brokers who mediate
  interactions between an investor (client) and the
  stock market (supplier).
• Generators are like interior designers who obtain
  material from manufacturers (products) on behalf
  of their clients.
• Reactors are like lawn service companies that
  respond to conditions in a lawn (target) on
  behalf of a homeowner (client).

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Summary

• There are hundreds of design patterns and they
  are hard to remember.
• One way to help remember them is to classify
  them.
• Our pattern collection is classified into three
  categories
• Broker patterns
• Generator patterns
• Reactor patterns