Design Patterns

Question 1

What kind of Design Patterns can generally be differentiated?

Answer 1

• Constructural Patterns
• Behavioral Patterns
• Creational Patterns

Question 2

Name examples for Structural Patterns

Answer 2

• Adapter
• Proxy
• Decorater
• Bridge
• Facade

Question 3

Name examples for Behavioral Patterns

Answer 3

• State Pattern
• Mediator
• Observer
• Strategy

Question 4

Name examples for Creational Patterns

Answer 4

• Factory Pattern
• Builder Pattern

Question 5

Describe the Adapter Pattern

Answer 5

• when two not compatible interfaces need to be connected an Adapter can be used
• wraps the one interface offering an compatible api to the other
• transforms the input into a format compatible to the wrapped interface

Question 6

Describe the Observer Pattern

Answer 6

• behavioral pattern
• if one components should be aple to notify other components about changes without needing to know who these other components are
• object should react to changes in subject without the subject knowing the observers
• subject only knows, that they implement the observer interface
• observer can register or unregister at any time
• subjects contains a list of observers of type observer interface
• subscribe method of subject takes interface type observer

Question 7

Describe the Decorater Pattern

Answer 7

• adds dynamically and transparently new functionality to a component without expanding the component itself
• base-component declares central interface for wrapper and wrappe, will be implemented by everyone
• concrete base-component is the wrappe, wrapped by one or multiple potential decoraters
• base decorater extend the base component and its method, and are implemented by concrete decoraters
• wrapped component does not care about being wrapped and has no knowledge of it
• decoraters have a field for the wrappee of the abstract type base-component

Question 8

Describe the Proxy Pattern

Answer 8

• structural pattern
• instead of communicating directly with a service, communication runs through a proxy that redirects requests to target service
• both service and proxy implement the same interface
• proxy has a field for the real service

Question 9

Describe the Facade Pattern

Answer 9

• Structural pattern
• a facade encapsulate logic and interfaces and makes specific information and functionality visible to the outside
• presents a simpified interface to a complex subsystem
• can also be used when a lot of technicall classes are used that are of no use for outside systems

Question 10

Describe the Bridge Pattern

Answer 10

• structural pattern
• seperates implementation from its interface allowing both to change independently
• switches from inheritance to object composition
• one dimension then contains the other dimension as an object
• both abstraction and implementation are interfaces, where abstraction contains an implementation
• both can be seperately implemented, decoupling them from each other
• usually abstraction declares complex interface methods that then call multiple implementation functions

Question 11

Describe the State Pattern

Answer 11

• Behavioral Pattern
• instead of being only an attribute the state becomes its own object
• these objects follow the same interface but have state-specific logic implemented in their overriding methods

Question 12

Describe the Mediator pattern

Answer 12

• behavioral pattern
• mediator controls how objects interact with each other
• instead of speaking with each other the objects only communicate with the mediator
• mediator decides what to do with communication and what other objects need to be contacted
• concrete mediators often keep list of all relevant objcets to be connected
• each component receives reference to mediator from abstract component interface

Question 13

Describe the Factory Pattern

Answer 13

• creational pattern
• instead of instancing new objects of certain types on their own components use an abstract factory of the abstract interface type of all these objects
• factory itself can be implemented to cover expandable type of object list

Question 14

Describe the Combinator Pattern

Answer 14

• allows to change multiple primitive operations of the same type together
• allows to create clear and reusable code