Æliens

behavioral patterns

deal with algorithms and the assignment of responsibilities between objects

class

• template method -- the skeleton of an algorithm
• interpreter -- to evaluate expressions

object

• mediator -- provides indirection for loose coupling
• chain of responsibility -- connect objects to interact
• observer -- to handle dependencies

encapsulating behavior

• strategy -- algorithm
• command -- request
• state -- object state -> behavioral change
• visitor -- to extract behavior from class
• iterator -- access and traversal

observer

structure

consequences

• abstract coupling between subject and observer
• support for broadcast
• deals with unexpected updates

implementation

• mapping subjects to observers
• observing more than one subject?
• who triggers the update - subject or client of subject
• dangling references to subject
• consistency of subject (before notification)
• adding observer-specific update protocols (push / pull)
• specifying modifications of interest (aspects)
• how to encapsulate update semantics