Head First Design Patterns: A Brain-Friendly Guide

Head First Design Patterns is an excellent introductory text for design patterns, plus object oriented design in general. Each chapter in the main part of the book covers one or two of the most common design patterns in great depth, including motivation, sample code, exercises, as well as answering many of the questions a reader is likely to have. Additionally, one of the things that makes the book great is that each chapter uses the context of the design pattern to introduce one or two important object oriented design principles such as the Open-Closed Principle and the Principle of Least Knowledge. Less common patterns are covered in the appendix, although in much less depth.I bought this book for my 17-year-old nephew -- who is in the second year of a high school computer programming course -- as a companion to the Gang of Four book. I think the two books work well together, with Head First Design Patterns working as a more accessible introduction to design patterns, and the Gang of Four book serving as a reference for later on. He definitely finds the Head First book easier to read as a beginner. Even I, with a college degree in Computer Science and 20 years in the software development industry, find it valuable, at least as a review.For those wondering about which edition they will get, I bought this book through Amazon and received the tenth anniversary edition, updated for Java 8. The main difference is that it takes advantage of the newly-introduced Lambda Expressions. Although the book uses Java throughout, C# developers will have little if any trouble with the examples. In many cases, the code is identical.Slight nitpick: Some of the patterns in the appendix are given short shrift in the interest of space. For example, the section on the Visitor Pattern leaves out the important fact that one of the main motivations for the pattern is to overcome the limitations of languages that support only single dispatch. Said another way, the Visitor Pattern is trivial to implement in languages that support multiple dispatch. For more detail on these design patterns, I recommend the Gang of Four book, or online resources.

I purchased this book about a year ago and devoted a number of hours each week going through it. I am a software developer by trade, but never took a computer science course in my life, mostly because I was self-taught as a kid and all of this pre-dated the Web by about 20 years.In any event, one area where I knew I was lacking was a formal understanding of design patterns. I was in the middle of a fairly large enterprise application, and while I was fully versed in Object Oriented Programming (and had even taught it in the past), I realized that everyone we were hiring out of college "spoke" a different language than I did, talking about singletons, factories, MVC, etc.This book covers those and many, many more, in a completely involving and revolutionary way. It's basically designed with the Java language in mind, but I'm a .Net developer, never having learned Java. However, the book is so thorough and intuitive, that I decided to do all of the examples in C# (close enough to Java that in many cases, there's almost a 1-to-1 relationship between my home-grown example and the one in the book.So for me, the book's benefit was two-fold: exposure to both design patterns and the Java language. In many cases, I was able to ".Net-ify" the examples to take advantage of specific features of .Net. A good example was in the Observer pattern where you have an object that changes over time, and other objects ("observers") need to be aware of this change. The book presents a language-agnostic approach, where the observable object registers all of its observers, and cycles through them notifying each one that it has changed. With .Net, it's much easier (and more appropriate) to implement this using events, where the observable object doesn't care who's watching, it just announces "I've changed!" and each observer can then decide how to handle that event.But I digress... ultimately, I just threw myself into this book, doing every example as written, and then modifying those examples to function with the .Net mentality. I even did all the pencil exercises, puzzles, etc. It's all part of the learning process, right?So, in a nutshell, if you need to learn design patterns, get this book. It's a lot of fun, and chock full of great information and examples that you'll be able to apply to your own projects right away.