System Design Patterns Flashcards
WHat can be represented by a class?
- real-world, external entities
- information entities
- abstract ‘metahpors’ and ideas
What are the 3 main design principles to aim for?
- Distribtuion of behaviours (decentralisation)
- Even granularit (components to have similar levels of complexity)
- Loose coupling (objects can be reused in another context)
Briefly describe CRC Card prototyping
+ low tech strategy for prototyping useful object concepts
+ flexible; allows the concept set to change
How do we write a CRC card? 3 steps
- Name concept accroding to main purpose
- Identify (up to 7) responsibilities: knowing, doing, enforcing (physical size constraints force decomposition)
- Identify collaborators (classes on which this one depend)
What do we put on the reverse side of a CRC card?
- categorise the card
- attributes (no remote get/set methods)
- constraints (business rules for attributes)
What are 3 ways to split a CRC card?
- 2 peer concepts; if responsibilties handle disjoint subset of attributes or collaborators.
- Parent-child concepts; if some responsibilties handle a subset of attributes or collaborators
- Subcontractor concepts; no obvious splitting move
Why focus on responsibilty for Responsibilty-Driven Design?
want to identfy objects which bear some responsibility for the system
- better than passive records which ancapsulate data
- better than abstract data types with just set/get methods
What are 3 methods of Transformation to reorganise communication-paths between subsystems?
- Delegation
- Encapsulation
- Refactoring
What is a design pattern?
reusable element of object oriented design
ready made solution to common design problems
Describe 3 typical uses of design pattern
- look out for problems in design; apply pattern
- design from scratch using patterns to get high-quality design
- retrofit extensions/adaptionsusing patterns
Describe the Bridge design pattern
reducing a number of specialised variants of a concept by encapsulating one varying dimension inside another
Describe the Mediator design pattern
introduce objects which handle communication between other objects
- removes need to couple objects directly
Describe the Chain of Responsibilty design pattern
give multiple objects the chance to handle a request
pass request along the chain
Describe the Command design pattern
encapsulate a funciton as an object with a single execture method, to add functions to a system incrementally
Describe the State design pattern
allows an object to alter its behaviour when its internal state changes
Describe the Template Method design pattern
generalise control algorithms to common skeleton code with dynamically bound subroutines
WHat problem does the abstract factory design pattern solve?
dependency among components
What are the benefits of having the mediator pattern?
good for uncoupling, simplifying communication paths
What design patterns indicate loose coupling?
Mediator, composite
What patterns indicate generic behaviour?
Command, template method, state, factory method
What patterns indiciate late design fixes?
Observer, Facade, Adapter
What are the benefits of having the command pattern?
indiciates modular system with extensible behaviour
what are the benefits of have the template method pattern?
indicates reusable basis for algorithmic design
What are the benefits of having the chain of responsibilty pattern?
indicates devolved responsibilty (single purpose objects)
