Design Patterns

Question 1

Advantages of Object Oriented Programming

Answer 1

Each Object easier to implement, maintain and reuse
- divide and conquer
Flexible combinations possible
- Versatility

Question 2

Disadvantages of Object Oriented Programming

Answer 2

Behavior distributed across multiple objects
- lack of clarity (Unübersichtlichkeit)
Any change of one object my affect many others
- interdependence

Question 3

Design Patterns - Observer Pattern
Communication without coupling

How and Why?

Answer 3

Decouple data model from parties/ observers that are interested in changes of its internal state

• Subject shouldnt know details of observers
• identity and number of observers may vary
• polling is inappropriate and inefficient (nachfrage obs ein update im subject gibt)

Question 4

Advantages of the Observer Pattern

Answer 4

• abstract coupling between subject and observer

- support for broadcast communication

Question 5

Disadvantages of the Observer Pattern

Answer 5

• update cascades
• update for all observers even though they may not be interested
• missing details about change
• limited communication interface -> subject cannot send optional parameters

Question 6

Observer Pattern - Implementation

who should inform observer of state change?

Answer 6

Method that changes the state notifies the observers
-> direct notification after change of state

Client triggerst update
-> if several changes performed at once only one notification needed

Question 7

Design Patterns - Factory Method

Participants

Answer 7

Product
- interface of objects created by factoryMethod()
ConcreteProduct
- implements product interface
Creator
- declares factory method that returns object of product
ConcreteCreator
- overrides factoryMethod() to return instance of conreteProduct

Question 8

Factory Methods - Consequences and Variants

Answer 8

• client code only knows product interface -> works with any specific concreteproduct class
• provides hook for subclasses

Variants

• creator abstract
• creator is concrete and provides default implementation

Question 9

Design Patterns - Abstract Factory

Motivation

Answer 9

For complete abstraction of the database
- clients only needs to interact with interface
avoid knowing the concrete type at creation time

Question 10

Abstract Factory - Consequences

Answer 10

+ abstracts away from concrete products
+ changing product families is easy
+ ensures consistency among products

• adding unforeseen kinds of products difficult
• client needs to know hot to use factory (interface) instead of constructor