Tuesday, 4 February 2014

Skimmer's Guide - Head First Design Patterns - Welcome To Design Patterns

“The best way to use patterns is to load your brain with them and then recognize places... where you can apply them. Instead of code reuse, with patterns you get experience reuse.”


I'm reading Head First Design Patterns along with a few others in the LJC Book Club. As we read, I'll produce a series of Skimmer's Guide posts for each significant section of the book. The previous section, on the Introduction, is here. If you are interested, please join the discussion on our Google+ community.


Continuing from the introduction, we now take a deep dive into the world of design patterns. Emphasis is on the ethos that "someone had already solved your problems" and how we can reuse the experience of others. Design patterns are our way of standing on the shoulders of giants!

Keeping with the Head First method, there are many lessons and even more ways to make the knowledge stick inside your brain. We may only cover the Strategy Pattern and general design concepts but you can rest assured you will remember all of it!


Exercise - Coding Ducks! (Strategy Pattern - p.18)
This simple exercise gives us our first opportunity to get our hands dirty :) It is a very straightforward problem and does an excellent job of teaching you the Strategy Pattern. I've pushed my work to Github: https://github.com/arkangelofkaos/head1st_designpatterns_duck

Exercise - Design Puzzle (p.25)
Make sure you have mastered the basics by trying your hand at organising the entity/class diagram in this exercise. Everyone remembers their UML arrows, right? ;)

Exercise - Crossword (p.33)
I know what you are thinking, we are learning and ain't nobody got time for messing around with a crossword! Rather surprisingly however, it is very valuable for seeing if you have been paying attention. Doing it exercises a different part of the brain and in the very least helped me notice I missed a page! Nevertheless it is incredibly frustrating if you're bad at crosswords!


Shared Vocabularly (p.26)
Communicating is one of the greatest challenges facing developers and learning to succintly transfer thoughts from your head to another person's is invaluable. Part of this is using the right language, which in our case is the language of Design Patterns. Learning all of this enables us to communicate faster as well as code faster!

Object Oriented Principles (p.30)

At the very heart of everything we are trying to do, there must be a firm foundation of solid object orientated principles. Design patterns work in tandem with these tenants, you must learn the practice and understand the wisdom behind it. All of this is reassuringly woven into the theme of the book: from subtly highlighting how "Inheritance is evil" to explicit recommendations (program to an interface!)


If you have little to no experience with the Strategy pattern, this chapter is a fantastic way for you to master the art of encapsulating varying behaviour. Even for those with some experience on the topic, the exercises both amuse and tax you, helping to reinforce our knowledge :)

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