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.”

FOREWORD

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.

WHAT IS THE ABOUT? 

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!

WHAT STOOD OUT? 

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!

IF YOU READ NOTHING ELSE... 

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!)

CONCLUSION

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 :)

London Code Dojo 30

Monday was London Code Dojo 30 and this time we were back in Barbican with the lovely people at valtech. 

WHAT WENT DOWN

The kata for the evening was based upon Fibonacci numbers... but with a twist! The problem was centred around Fibonaccimal Numbers (link) which use the Fibonacci numbers as a base for representing numbers. So taking 1, 2,3,5 and 8 as a base, we can represent 9 as 10001 or 01101. As you can see, some numbers can have multiple representations and this added to the complexity of the problem. For the majority of the evening I paired with Rob and I found it really valuable getting his insight into the problem! The code we produced for the night can be found here: https://github.com/arkangelofkaos/CodeDojo30_Fibonacci

MY IMPRESSIONS

Nothing beats a good plan

More so then anything else, I came to appreciate the value of having a solid plan. Having a high level design which everyone agrees will solve the problem is incredibly important. Test driving code doesn't magically produce well designed algorithms.

LESSONS LEARNT

Decompose complexity into simple functions

Functional concepts supplement object oriented coding in a fantastically seamless way. When dealing with collections or calculations it is surprising how  higher order functions like map and reduce translate to how you naturally think about the problems.

For instance, to produce all the Fibonaccimal representations of a number, you can use a two step process:

1. Find all unique ways to express that number as a sum of different Fibonacci numbers 
• For example: 3 is [3] and [2+1]
2. Translate each way into the corresponding Fibonaccimal 
• [3] is 100 and [2+1] is 011

These steps are both mapping a number to a list of lists, then each list to a String. This is reflected in the code below:

return sumsCalculator.fibonacciSumsFor(number) // Step 1

                             .parallelStream()

                             .map(toStringCalculator::fibonacciSumToString); // Step 2

Suddenly I've decomposed an abstract problem into two concrete functions which I understand and can test drive!

Perhaps this is the crux behind solving all problems. Reduce the complexity until the solution is series of simple steps. Needless to say, making things simple is not simple... But there in lies the rub :)

Skimmer's Guide - Head First Design Patterns - Introduction

“Our goal was to make the book weigh less than the person reading it... Our focus is on the core patterns that matter...”

FOREWORD

I've recently started reading this book along with a few others in the LJC Book Club. As we read the book, I will be producing a series of Skimmer's Guide posts for each significant section of the book. Introduction to Design Patterns, the next section, is here. If you are interested, please join the discussion on our Google+ community. 

WHAT IS THE ABOUT? 

We start our reading of Head First Design Patterns with a gentle and enlightening introduction to the Head First world. Their approach is really intriguing and it is refreshing how much they are vested in helping the reader learn. Everything is to the point and we are immediately told who this book is and isn't for. Our goal in reading this book is stately clearly: learning that design patters are all about reusing experience and creating flexible code.

Despite the daunting size of this book (it is very heavy), the writing style and format makes it very easy and enjoyable to read. If you have experience with Head First books in the past, the introduction could be skipped although I highly recommend giving it a quick skim in the least.

WHAT STOOD OUT? 

Taster - Table of contents

Surprisingly enough, the novel table of contents work really well as a taster for things to come. Much like the rest of the book, the entertaining writing style brings the book to life :)

IF YOU READ NOTHING ELSE... 

Tricking your brain into retaining knowledge

One of the very first concepts covered in the book, this is the art of learning how to best learn. Absolute must read as the techniques covered are applicable to learning in all walks fo life.

CONCLUSION

Beginning to read this book has been a wonderful foray into the Head First world and has whetted my appetite for more. Looking forward to sinking my teeth into the world of design patterns in the next part :D