1. GRASP

2. 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.

3. The 9 GRASP Information Expert Creator
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 A[s]
B is an information expert for A (has the constructor arguments).

4. The 9 GRASP … Controller Low coupling High cohesion
Who handles a system event?
The system’s façade [controller] class.
Low coupling
Minimize inter-class coupling
High cohesion
Maximize intra-class cohesion

5. 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

6. 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 (book’s example).

7. 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?  )
Client
Mediator
Service

8. 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();
for ( Iterator i = c.iterator(); i.hasNext(); ) {
doSomething( i.next() ); }
Java List, Map interfaces.
Create protected variations only around an area of instability.