Design Patterns

COMP 310 Java Resources Eclipse Resources

Design patterns as expressions of CS principles:

Question: Why are there only a few types of bridges in use today? There are only 4-6 different types of bridges, depending on who you ask: See for instance:. http://en.wikipedia.org/wiki/Bridge or http://library.thinkquest.org/J002223/types/types.html.

Design Pattern	CS Principle(s)
Union	Polymorphism, inheritance
Composite	Recursive data structures
Visitor	Decoupled data and algorithms
Extended Visitors	Decoupled data and algorithms with variant hosts
Strategy	Delegation to abstract processes/behaviors with known semantics
Command	Delegation to abstract processes/behaviors with unknown semantics
State	Dynamic reclassification -- objects that have changeable states and hence changeable behaviors. Also, encapsulation barriers to decouple changes.
Model-View-Controller	Decomposition of a system into interacting, yet decoupled modules
Adapter	Use of indirection layers for decoupling and communication via syntactic translations
Intepreter	Data-driven algorithms, polymorphic dispatching, and recusion.
Abstract Factory	Abstraction of the creation process of an entity
Template	Concrete process involving abstract behaviors.
Singleton	Uniqueness
Null Object	Concept of "zero" (something that represents nothingness)
Observer-observable	Decoupled communications from a single sender to multiple receivers.
Decorator	Encapsulation barriers/indirection layers to intercept and modify processing paths.
Flyweight	Resource pooling

To look for design patterns in the problem is to look for the underlying CS principles that are driving it. The design patterns and the abstract notions that they represent comprise the "chunks" into which a problem is decomposed in order to understand it -- "Abstract decomposition"