Design Patterns

Question 1

What is a design pattern?

Answer 1

A design pattern is a way of reusing abstract knowledge about a problem and its solution. The pattern is a description of the problem and the essence of its solution.

Question 2

(True or False) Design patterns should not be abstract. They need to be specific to be used in a variety of settings.

Answer 2

False! They actually need to be abstract to be applied in different settings.

Question 3

What, in particular, are patterns?

Answer 3

Patterns (and pattern languages) are ways to describe bes praticies, good designes, and capture experience in a way that is possible for other to reuse this experience.

Question 4

What are pattern elements?

Answer 4

1. Name
2. Problem description
3. Solution description (not an actual design byt a template for a solution that can be instantiated in different ways)
4. Consequences (the rults and trade-offs of applying the pattern.

Question 5

What is the Observer Pattern?

Answer 5

The Observer pattern is a behavioral design pattern that establishes a one-to-many relationship between a subject and its observers, allowing multiple observers to automatically receive updates when the subject’s state changes. It promotes loose coupling, enabling observers to react to changes without tightly binding them to the subject.

Question 6

What is pub-sub?

Answer 6

Pub sub is a subscribing system. It can also bee seen as real-time updates from the source to the application. This pairs most with the observer pattern.

Question 7

What are the design pattern classes?

Answer 7

1. Creational design patterns (dealing with class instantiation and object creation, effective inheritance, object delegation)
2. Structural design patterns (defines inheritance to compose interfaces, construction of objects to obtain new functionality)
3. Behavioral Design Patterns (explores class and object communication, interaction between objects)

Question 8

(Creational Design Patterns) What is Abstract Factory?

Answer 8

Creates an instance of several families of classes.

Question 9

(Creational Design Patterns) What is Builder?

Answer 9

Separates object construction from its representation.

Question 10

(Creational Design Patterns) What is Factory Method?

Answer 10

Creates an instance of several derived classes

Question 11

(Creational Design Patterns) What is Object Pool?

Answer 11

Avoid expensive acquisition and release of resources by recycling objects that are no longer in use. (Library pre-creates instances of books for checkout)

Question 12

(Creational Design Patterns) What is Prototype?

Answer 12

A fully initialized instance to be copied or cloned. This helps us to see what kind of edits we want. When we decide, we create a copy and then edit that.

Question 13

(Creational Design Patterns) What is Singleton?

Answer 13

A class of which only a single instance can exist.

Question 14

(Creational Design Patterns) What is Adapter?

Answer 14

Match interfaces of different classes. We make two things work together like an adapter. An adaptor creates an intermediary abstraction that translates, or maps, the old component to the new system.

Question 15

(Creational Design Patterns) What is Decorator?

Answer 15

Add responsibilities to objects dynamically. (You add functionality to existing objects like scroll bars)

Question 16

(Creational Design Patterns) What is Facade?

Answer 16

A single class that represents and entire subsystem. (Hides complexity and acts like a wrapper)

Question 17

(Creational Design Patterns) What is Proxy?

Answer 17

An object representing another object. (EX: a check is a proxy for the actual money. The bank checks the proxy and then puts the money in your account.)

Question 18

(Creational Design Patterns) What is Iterator?

Answer 18

Sequentially access the elements of a collection. (An example is a map program. Once you’ve hit this step, this is your next direction)

Question 19

(Creational Design Patterns) What is Memento?

Answer 19

Capture and restore an objects internal state. (There are two examples; Google Docs, and Google pages.

Google docs - Lockbox is the current state of the document and the caretakers are the editors.
Google pages - Google asking if you want to restore the pages when they suddenly closed.

Question 20

In what interface is proxy most commonly used?

Answer 20

In layered architecture. We can get the information we need without breaking the interface.

Question 21

What is the difference between adapter, proxy, and decrator?

Answer 21

Adapter provides a dofferent interface.
Proxy provides the same interface.
Decorator is more transparent to the client.