GRASP

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GRASP
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GRASP

• GRASP an acronym that stands for
• General
• Responsibility
• Assignment
• Software
• Patterns
• I think a RAP is a better acronym.
• Do the words general software pull their
  weight?
• Referring to the 9 heuristics as patterns is a
  stretch.

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The 9 GRASP

• Information Expert
• Information expert the class that has the
  information necessary to fulfill the
  responsibility.
• Assign a responsibility to the information
  expert.
• Creator
• Who creates instances of class A?
• Class B when
• B has As
• B is an information expert for A (has the
  constructor arguments).

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The 9 GRASP

• Controller
• Who handles a system event?
• The systems façade controller class.
• Low coupling
• Minimize inter-class coupling
• High cohesion
• Maximize intra-class cohesion

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The 9 GRASP Polymorphism

• To vary a general behavior by class, extend a
  base class.
• Example Command pattern.
• The Lectures page links to the java files below
• These classes illustrate bad as well as good
  style.
• Cell.java CellImpl.java
• ActionItem.java
• ExpressItem.java
• APTSpawn.java

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The 9 GRASP Pure Fabrication

• Assign a highly cohesive set of responsibilities
  to a class that is
• Not in the application domain
• Created to support OOD
• High cohesion
• Low coupling
• Examples
• Façade, adaptor, bridge patterns are pure
  fabrications that lower coupling.
• PersistentStorage class (books example).

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The 9 GRASP Indirection

• Mediate
• Acting through an intervening agent.
• To interpose between parties, esp. for the
  purpose of effecting an agreement as, to mediate
  between nations.
• A client/service mediator class.
• Lowers coupling
• Examples Façade, Adaptor, Bridge
• (Sound familiar? ? )

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The 9 GRASP Protected Variations

• Define a stable interface to hide an area of
  instability.
• Yes
• List list new ArrayList() // java.util.List
  not java.awt.List
• No
• ArrayList list new ArrayList()
• Yes
• for ( Iterator i c.iterator() i.hasNext() )
  
• doSomething( i.next() )
• Yes
• Java List, Map interfaces.
• Yes
• Create protected variations only around an area
  of instability.