Chapter 4 - Design Patterns

Question 1

Which kinds of Patterns are there?

Answer 1

Idioms: Usage of programming language features, Design Patterns: teams of interacting objects and classes, Architecture Patterns: building blocks of software architecture

Question 2

What is good Class Design?

Answer 2

minimize visibility of classes and members (private as default), minimize mutability, single responsibility (class should only do one thing), naming (simple & expressive names)

Question 3

What is SOLID?

Answer 3

SRP, OCP, LSP, ISP, DIP

Question 4

What is SRP?

Answer 4

Single Responsibility Principle: separation of concerns, changes to a class should have only a single reason

Question 5

What is OCP?

Answer 5

Open-Closed Principle: classes closed for modifications, but open for extensions

Question 6

What is LSP?

Answer 6

Liskov Substitution Principle: derived class must fulfill the contract of its base class

Question 7

What is ISP?

Answer 7

Interface Segregation Principle: clients should not depend on interfaces they don’t need, if possible many small interfaces instead of one big

Question 8

What is DIP?

Answer 8

Dependency Inversion Principle: high level components should not depend on low-level components, changes in lower level must not impact higher layers

Question 9

what is the motivation of design patterns?

Answer 9

reuse is a main incentive, design can be best reused of all thing

Question 10

Name types of Design Patterns

Answer 10

creational patterns: encapsulate creation process, Structural patterns: compositions of classes and objects, Behavioral Patterns: how do objects work together? collaboration patterns

Question 11

Define the Singleton Pattern

Answer 11

ensure that there is only a single instance of a class, provides global access point to this instance

Question 12

Define Factory Method

Answer 12

defines interface for creating an object, subclass decides what objects are being created

Question 13

Define Abstract Factory

Answer 13

provides an interface for creating families of related or dependent objects without specifying their concrete classes

Question 14

Define Adapter

Answer 14

convert interface of a class into an interface expected by clients (also known as Wrapper)

Question 15

Define Bridge

Answer 15

decouple abstraction from its implementation such that both can vary independently, avoid strong coupling between abstraction and implementation

Question 16

Define Decorator

Answer 16

attach additional responsibilities to an object dynamically, decorator delegates operations to component object

Question 17

Define Observer

Answer 17

changing the state of an objects notifies all dependent so they can update, subject knows all its observers and notifies them or Observer defines updating interface

Question 18

what is FCoI?

Answer 18

Favour Composition over Inheritance: erwendet man Funktionalität wieder durch das Ableiten von einer Klasse, so ist die Subklasse abhängig von der Elternklasse. Dies macht ein System in vielen Fällen unnötig komplex, schlechter testbar und erschwert das Austauschen von Funktionalität zur Laufzeit.Bei der Komposition verwendet eine Klasse eine andere. Verwendet man dazu eine klar definierte Schnittstelle, fördert das die Entkopplung. Auch können verschiedene Implementationen einfach ausgetauscht werden. Bevor man sich also der Liskov Substitution stellt, fordert Favour Composition over Inheritance, sich die Frage zu stellen, ob man der Komposition nicht Vorrang geben kann.