Design Pattern Implementation in Java and AspectJ

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Design Pattern Implementation in Java and AspectJ

• Jan Hannemann, Gregor Kiczales
• OOPSA 2002

2003. 5. 27 Presented by Cheolho Kim
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Contents

• Introduction
• Experiment Format
• Result 1 Observer Pattern
• Result 2 Other Patterns
• Analysis
• Related Work
• Conclusion

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Introduction(1/3)

• GoF(Gang Of Four) Design Patterns
• E. Gamma, R. Helm, R Johnson, J. Vlissides
• Collected 23 design patterns
• Conveys the essence of a proven solution to a
  recurring problem
• Regarded as useful solution to certain type of
  design problems

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Introduction(2/3)

• Three most important challenges of patterns
• disappearing into the code problem
• This make it hard to distinguish between the
  pattern and the object model involved
• Documentation problem
• Because of invasive nature of pattern code, it is
  difficult to trace a particular instance if
  multiple patterns are used
• Pattern composition problem
• It is difficult to reason about systems with
  multiple patterns involving the same classes

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Introduction(3/3)

• Initial experiment to develop and compare Java
  and AspectJ implementations of the GoF patterns
• Crosscutting structure between roles and
  participant classes exists
• Modularizing the crosscutting structure improves
  the implementation of patterns
• 17 of 23 patterns implemented in AspectJ are
  improved in reusability, composability and
  (un)pluggability

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Experiment Format

• Comparative analysis of Java and AspectJ
  implementation of the GoF design patterns
• Java implementations corresponds to the sample
  C implementation in the GoF book
• AspectJ implementations are selected among 57
  different implementations to fully investigate
  the design space of each pattern

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Result 1 Observer Pattern(1/4)

• What is observer pattern?

The Observer pattern describes how to establish
these relationships - Subject may have any number
of dependent observers. - All observers are
notified whenever the subject undergoes a change
in state. - Each observer will query the subject
to synchronize its state with the subject's state.
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Result 1 Observer Pattern(2/4)

• Implementation in Java

1. Code for implementation is spread across the
classes 2. All participants have to know about
their role in the pattern

• Changes requires modification in all
  participating classes
• adding or removing a role
• using alternative notification mechanism

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Result 1 Observer Pattern(3/4)

• Implementation in AspectJ

Specific parts to each instantiation
1. Give each role to a class 2. Set of changes of
interest on the Subject 3. Means of updating each
Observer
Concrete subaspect
Abstract aspect
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Result 1 Observer Pattern(3/4)
Abstract aspect

• Implementation in AspectJ

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Result 1 Observer Pattern(3/4)

• Implementation in AspectJ

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Result 1 Observer Pattern(4/4)

• Improved properties of implementation in AspectJ
• Locality
• All the code that implements the pattern is in
  the abstract and concrete aspects
• No coupling between the participant classes
  exists
• Reusability
• Core pattern code(ObserverProtocol) is abstracted
  and reusable
• For each pattern instance, only define one
  concrete aspect
• Composition transparency
• Even if a class takes part in multiple observing
  relationships, codes of the class and pattern are
  not confused
• (Un)pluggability
• Participants need not be aware of their role
• It is easy to switch between using a pattern or
  not using it

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Result 2 Other Patterns

• Composite, command, mediator, chain of
  responsibility
• Roles only used within pattern aspect
• Singleton, prototype, memento, iterator,
  flyweight
• Aspects as object factories
• Adapter, decorator, strategy, visitor, proxy
• Language constructs
• Abstract factory, factory method, template
  method, builder, bridge
• Multiple inheritance
• State, interpreter
• Parts of scattered code can be modularized
• Façade
• No benefit from AspectJ

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Analysis (1/4)

• Analysis is broken into three parts
• General improvements observed in many pattern
  re-implementation
• Specific improvements associated with particular
  patterns
• Origins of crosscutting structure in patterns
• Observed improvements correlate with the presence
  of crosscutting structure

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Analysis (2/4)

• General improvements
• Locality
• 17 of 23 GoF patterns
• All dependencies between patterns and
  participants are localized in the pattern code
• Reusability
• 12 of 17 localized patterns
• By separating pattern-specific code, participant
  and pattern can be reusable in other contexts
• Transparent composability
• 14 of 17 localized patterns
• A class or object can have different roles in
  different pattern instances without confusion
• (Un)pluggability
• Reusability and adaptability of patterns

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Analysis (3/4)

• Specific improvements
• Singleton case
• AspectJ provides design choices
• Singleton property is implemented as inherited
• Constructor instead of a devoted factory method
  can be used
• Multiple inheritance and Java
• AspectJ provides a way of implementing patterns
  having multiple-inheritance with transparent
  composability
• Breaking cyclic dependencies

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Analysis (4/4)

• Crosscutting structure of design patterns
• Crosscutting in pattern structure is caused by
  different kinds of roles and their interaction
  with participants
• Roles
• Defining roles - define the participants
  completely
• Superimposed roles - assigned to classes
• Roles crosscut participant classes
• Conceptual operations of interest crosscut
  methods
• Roles from multiple patterns crosscut each other

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Related Work (1/2)

• Design patterns and language paradigms
• Investigation of pattern applicability in other
  language paradigm
• Pattern libraries and tool support
• Automation of design and code generation
• Pattern classification
• Classifying existing patterns in order to reduce
  the number of distinct patterns or to pinpoint
  relationships

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Related Work (2/2)

• Roles and pattern composition
• Approaches to model roles and their relationship
  to the concrete classes playing those roles
• Alternative pattern representations
• Approaches to design pattern notation

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Conclusion

• Improvement from using AspectJ manifest
  themselves as a set of properties related to
  modularity
• Reusability, composition transparency,
  (un)pluggability
• Improvement is directly correlated to the
  presence of crosscutting structure in the
  patterns
• Future work
• Applying AspectJ to other patterns
• Comparing the results with the use of other AOP
  techniques

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