Design Patterns and Components

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Design Patterns and Components

• Prepared by Mehmet Bilsay KARADENIZ

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Design Patterns

• Reusable solutions to recurring design problems
  in OO systems.
• It describes the problem, the solution, when to
  apply the solution, and its consequences.
• It also gives implementation hints and examples.
• The solution is a general arrangement of objects
  and classes that solve the problem.

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Others

• Anti-Patterns
• Things you souldnt do.
• AbstractionInversion(From less to more complex)
• Analysis Paralysis (Too much analyse)
• ...

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Desing Patterns
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CreationalPatterns
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StructuralPatterns

• Patterns that use various language mechanisms for
  structuring code and assembling objects .

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Behavioral Patterns
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Singleton

• If a system only needs one instance of a class,
  and that instance needs to be accessible in many
  different parts of a system, you control both
  instantiation and access by making that class a
  singleton.
• Impementation
• Static GetInstance
• Private Constructor
• Monostate All functions are static

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Singleton
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AbstractFactory
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AbstractFactory
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Adapter

• Lets classes with incompatible interfaces work
  together.
• Convert the interface of some class b into an
  interface a that some client class c understands.
• Implementation
• Create a class that has the desired interface
  from some other class.

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Adapter
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Facade

• Defines a higher-level interface that makes the
  subsystem easier to use.
• Provide a unified interface to a set of
  interfaces in a subsystem.
• Hides complexity.
• Implementation
• Create a class that has the desired simple
  interface from more complicated classes that has
  more detailed interfaces.

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Facade
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Other Practices

• Implement according to interfaces.
• Dont use inheritance. It breaks abstraction.
• Use delegation instead of inheritance.
• Generics are hard to understand use with caution.
• Applications are hard to design, toolkits (class
  libraries) are harder, and frameworks are the
  hardest to design.

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Design Patterns Criticism

• Dont let enoug code reuse.
• In practise it is not always efficient.
• Most of them are missing language features (16 of
  23).
• Do not solve a problems, gives tools.

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Component Orientation

• Uses most core practises of design patterns.
• Adresses most of the drawbacks.
• ClassFactory, Adapter, ... etc can be widely used
  in component oeriented software design.
• Component Design Patterns. Not meature enough.

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Component Design Patterns

• Distribution Patterns
• DistributionOfComponents
• LayeredComponentFramework
• BypassableAbstraction
• LocationAbstraction
• ReplicatedObject
• FacadeAtTheDistributionBoundary
• ChokePoint
• Connection Patterns
• InterfaceDiscovery
• ConnectionSingleton
• ConnectionFlyweight
• ConnectionObserver
• Interaction Patterns
• AbstractInteractions
• ThirdPartyBinding
• ComponentGlue

• Behavior Patterns
• ContainerIndependence
• EnvironmentalAcquisition
• ContainerManagedBehavior
• ComponentManagedBehavior
• DistributedCommand
• InterruptibleCommand
• TransactionalCommand
• CommandConcurrency
• Deployment Patterns
• IndividualPackaging
• GroupPackaging
• PrebuiltFunctionality
• AutomatedAssembly

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Component Orientation Criticism

• Dependency to other firms.(interface and
  strategy)
• Development of components are harder.
• Non-Standart (and possibly incompatible)
  component protocols.
• (COM,XPCOM,CORBA,...)
• High learning delta.(coupled with big projects)

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Component Orientation and Patterns

• High learning delta and dependecy to other firms
  and component technologies can be reduced with
  adapter and bridge.
• Design what you need or design with what you have
  ?
• Which direction should we take ?

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Thank you
Questions ?
Referances
http//www.c2.com/cgi/wiki?AreDesignPatternsMissin
gLanguageFeatures http//en.wikipedia.org/wiki/Des
ign_pattern_(computer_science) Gamma, Erich,
Richard Helm, Ralph Johnson, and John Vlissides
(1995). Design Patterns Elements of Reusable
Object-Oriented Software, Addison-Wesley. ISBN
0-201-63361-2. http//www.dofactory.com/Patterns/P
atterns.aspx
Prepared by Mehmet Bilsay KARADENIZ