Design Patterns

Question 1

Is “separate the parts of the code that changes from what stays the same” a design principle?

Answer 1

Yes

Question 2

Is “Program to an interface, not an implementation” a design principle?

Answer 2

Yes. Could be also program to a super type which can be replaced by something else

Question 3

Is “Favor composition over inheritance” a design principle? Why?

Answer 3

Composition makes it easier to swap behavior. Inheritance is good to avoid code dup but maintenance is shitty

Question 4

Is Strategy Pattern a design pattern? What does it say?

Answer 4

Yes. It defines a family of Algorithms, encapsulates them and makes them interchangeable.

Question 5

What else does design patterns offer other than better maintenability?

Answer 5

Gives a shared vocabulary among developers. Patterns allow you to say more with less.

Question 6

What does the observer pattern do?

Answer 6

The Observer Pattern defines a one-to-many dependency between objects so that when one object changes state, all of its dependents are notified and updated automatically.

Question 7

What does the Decorator pattern do?

Answer 7

Wraps alike classes one on top of the other to compound results. Example sum the cost of add-ons of the milkshake

Question 8

What does the The Factory Method Pattern do?

Answer 8

defines an interface for creating an object, but lets subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses.

Example: build new customer() passed as argument to a class.

Question 9

What does The Dependency Inversion Principle say? Is it OO?

Answer 9

Depend upon abstractions. Do not depend upon concrete classes. Yes

Question 10

What does the command Pattern say?

Answer 10

The Command Pattern encapsulates a request as an object, thereby letting you parameterize other objects with different requests, queue or log requests, and support undoable operations.

Question 11

What does the adapter pattern say?

Answer 11

The Adapter Pattern converts the interface of a class into another interface the clients expect. Adapter lets classes work together that couldn’t otherwise because of incompatible interfaces.

Question 12

What does the facade pattern do?

Answer 12

The Facade Pattern provides a unifi ed interface to a set of interfaces in a subsytem. Facade defi nes a higherlevel interface that makes the subsystem easier to use.

Question 13

What’s the Template Method Pattern?

Answer 13

The Template Method Pattern defi nes the skeleton of an algorithm in a method, deferring some steps to subclasses. Template Method lets subclasses redefi ne certain steps of an algorithm without changing the algorithm’s structure.

Example: OnCalculate ()

Question 14

What is the Hollywood principle and what design pattern implements it?

Answer 14

The Hollywood Principle Don’t call us, we’ll call you. The template Method Pattern

Question 15

What does the iterator pattern do?

Answer 15

The Iterator Pattern provides a way to access the elements of an aggregate object sequentially without exposing its underlying representation.

Question 16

What’s the single responsability principle say?

Answer 16

A class should have only one reason to change.

Question 17

What is the composition pattern?

Answer 17

The Composite Pattern allows you to compose objects into tree structures to represent part-whole hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly.

Example: tree of objects

Question 18

What does the state pattern say?

Answer 18

The State Pattern allows an object to alter its behavior when its internal state changes. The object will appear to change its class.

Question 19

What is the chain of responsibility design pattern?

Answer 19

Chain of Responsibility is behavioral design pattern that allows passing request along the chain of potential handlers until one of them handles request. The pattern allows multiple objects to handle the request without coupling sender class to the concrete classes of the receivers.