Ch 7: Object Oriented Design

Question 1

Important Concepts

Answer 1

• Object Oriented Programming
• Class Diagrams
• Inheritance
• OOP Design Steps
• Design Patterns

Question 2

What are Design Patterns?

Question 3

Goal of good Object Oriented Design

Answer 3

To create elegant, maintainable code arranged into objects.
Design is NOT about regurgitating known Design Patterns.

Question 4

Object Oriented Design Steps

Answer 4

1. Handle Ambiguity
2. Define Core objects
3. Analyze Relationships
4. Investigate Actions

Question 5

Object Oriented Design Steps:
1. Handle Ambiguity

Answer 5

Questions/Problems are often vague(intentionally in interviews, less intentionally in real life)

Ask Clarifying questions:
* Use the “Six W’s”:
- WHO is going to use it
- WHAT
- WHY
- WHERE will it be used
- WHEN will it be used (time, frequency of use, etc)
- HOW are they going to use it

Question 6

Object Oriented Design Steps:
2. Define Core Objects

Answer 6

• Determine what the most fundamental objects should be, can be revised as the process goes on
• Objects may represent real world counterparts(user, company, building, etc)
• Objects may be abstract: (session, time block, requests, etc)

Question 7

Object Oriented Design Steps:
3. Analyze Relationships

Answer 7

• Consider the relationships between the objects created so far
• Which are “members” of other objects
• Which objects inherent from a parent object(or could)
• Is the relationship many-to-one, many-to-many, one-to-one?

Question 8

Object Oriented Design Steps:
4. Investigate Actions

Answer 8

Assess the Key Actions that objects take, and how they relate to other objects.
Likely to have forgotten some objects

Question 9

Design Patterns:
Two Extremely Common Design Patterns in Interviews

Answer 9

• Singleton
• Factory Pattern

(Note: you should know many more design patterns than these)

Question 10

Singleton Pattern:
Overview

Answer 10

• Ensures that a class has only one instance
• Ensures access to the instance through the application
• Useful for “global” objects with exactly one instance
• Many people dislike the Singleton design pattern
  
  • Sometimes called an “anti-pattern”
  • Can sometimes interfere with Unit Testing

Question 11

Factory Design Pattern:
Overview

Answer 11

• Offers an interface for creating an instance of a class
• Subclasses decide WHICH class to instantiate
• Factory method takes a parameter representing WHICH class to instantiate
  
  • Constructs and returns an instance of the specified class
• Typically has a Creator class
  
  • Either abstract or concrete with an implementation of the Factory method

Question 12

OOP Design Principles:
10 Key Principles

Answer 12

• DRY (Don’t Repeat Yourself)
• Encapsulate What Changes
• Open Closed Design Principle
• Single Responsibility Principle(SRP)
• Dependency Injection or Inversion Principle
• Favor Composition over Inheritance
• Liskov Substitution Principle (LSP)
• Interface Segregation Principle (ISP)
• Programming for Interface not Implementation
• Delegation Principles

Page: https://hackernoon.com/10-oop-design-principles-every-programmer-should-know-f187436caf65