SOFTWARE DESIGN AND ARCHITECTURE LECTURE 31. Review Creational Design Patterns – Singleton Pattern...
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Transcript of SOFTWARE DESIGN AND ARCHITECTURE LECTURE 31. Review Creational Design Patterns – Singleton Pattern...
SOFTWARE DESIGN AND ARCHITECTURE
LECTURE 31
Review
• Creational Design Patterns– Singleton Pattern– Builder Pattern
Outline
• Behavioral Patterns– Observer Pattern– Chain of command
Behavioral Patterns
• characterize the ways in which classes or objects interact and distribute responsibility.
• Behavioral class patterns:– use inheritance to describe algorithms and flow of
control• Behavioral object patterns:– describe how a group of objects cooperate to
perform a task that no single object can carry out alone.
OBSERVER
Observer Design Pattern
Intent– Define a one-to-many dependency between objects so
that when one object changes state, all its dependents are notified and updated automatically.
• Encapsulate the core (or common or engine) components in a Subject abstraction, and the variable (or optional or user interface) components in an Observer hierarchy.
• The "View" part of Model-View-Controller.
Chain of Responsibility• Intent:– Avoid coupling the sender of a request to its receiver by
giving more than one object a chance to handle the request.
– Chain the receiving objects and pass the request along the chain until an object handles it.
• The pattern chains the receiving objects together, and then passes any request messages from object to object until it reaches an object capable of handling the message.
• The number and type of handler• objects isn't known a priori, • they can be configured dynamically.
Summary
• Behavioral Patterns– Observer Pattern– Chain of command