Holub on Patterns

James Edward Gray II writes "Apress sent me a copy of Holub on Patterns for review, and for that I'm extremely grateful, because this is a gem of a book I would not have liked to miss. Odds are, most object-oriented programmers will feel the same, so allow me to share the highlights." Read on for the rest of Gray's review. Holub on Patterns: Learning Design Patterns by Looking at Code author Allen Holub pages 414 publisher Apress rating 9 reviewer James Edward Gray II ISBN 159059388X summary Design Patterns taught through Real World Programs.

If I can level any complaint against this book, it's probably that the title doesn't properly convey the goodness locked within. Holub on Patterns is short for Allen Holub on Design Patterns. Allen Holub is a long time expert on Design and Design Patterns, so he's the man you want to learn it from. Still, if I could name this book, it would be Object Oriented Design Voodoo. (Note: This is probably why I don't work for Apress or any other publisher.)

The book's subtitle is "Learning Design Patterns by Looking at Code." That probably conveys the work's focus a little better and it also gives away one of the book's best features: sensational examples. (These examples are in Java, another area where Holub is a well-known authority, but the concepts taught apply to Object Oriented Programming in any language.)

Titles aside, this book really is the best work I've read on design patterns. If you don't already know, design patterns are the recurring patterns of object-oriented software implementations. Luckily, you don't have to know anything about them to read this book. The author covers many patterns in rich detail from the beginning. Even if you do know your design patterns well, I'll wager Holub still has a trick or two to impress you with.

Holub discusses patterns in their ideal pure form, but much more importantly he shows them as they occur "in the wild," with multiple variations. He covers the downside of each pattern, weights the trade-offs of using them, and even gives a handful of cases where he felt they were impractical. He does all this right in the middle of complex real-world examples so you can see each point he's making. That's actual programming, folks. The good, the bad and the choices we programmers make are well presented, and that's rare in a programming text.

The book opens with two chapters that more or less cover why we need design patterns at all. Did you know getters/setters are bad? Did you know that subclassing is dangerous? If you said No to either question, you need this book and these two chapters in particular will get you up to speed on good OO practices. This section of the book is mostly theory, light on examples.

The next two chapters (covering over 250 pages) make up the heart of the book. Holub examines two examples in exhaustive detail. The first is his implementation of The Game of Life. You've probably implemented that on your TI calculator, but Holub sure didn't. He admits that his implementation is "Toy Code," but it's a robust example that involves eleven design patterns. The second example is production code, a mini database complete with SQL interpreter. This code is also swimming in pattern usage, and Holub gives you the guided tour.

I've already said these examples are great, but that claim begs some elaboration. First, we're talking about hundreds of lines of code in many of these listings. These aren't the usual contrived junk. What's more, one class may be participating in multiple patterns. Making any sense of these examples would be almost impossible if the author wasn't flawless in explaining the key points and always dropping hints about what you need to notice. This isn't light reading. It's work, but the rewards are there and it'll pay off if you really spend the effort to understand how the code works.

Finally, the book closes with an appendix that gives more typical recipe-card style listings of all the design patterns discussed throughout the text. This is a nice reference after you've finished the tricky stuff. If you're new to design patterns, you might start here, before the book throws you into the lion's den with its massive examples.

Just in case I haven't sold you on this title yet, I better mention the gorgeous hard back binding. Brilliant and sexy. How can you beat that?

Holub on Patterns is a very approachable way to learn a lot about design patterns. If you already know how much patterns can improve your object-oriented programming, you'll really enjoy Holub's presentation of the topic. If you don't yet grasp Design Patterns or haven't enjoyed other works on the subject, you'll just have to trust me: You want this book.

You can purchase Holub on Patterns: Learning Design Patterns by Looking at Code from bn.com. Slashdot welcomes readers' book reviews -- to see your own review here, read the book review guidelines, then visit the submission page.

Comments

Official site

[the_mighty_$]

The official site is located here.

Getters/setters bad?

[d_jedi]

The book opens with two chapters that more or less cover why we need design patterns at all. Did you know getters/setters are bad? Did you know that subclassing is dangerous? If you said No to either question, you need this book and these two chapters in particular will get you up to speed on good OO practices.

Can someone explain why accessor and mutator methods (I assume this is what he means by "getters/setters") are bad?

Re:Getters/setters bad?

[philci52]

In the first case, you don't need getters and setters because the members are already public.

Having public members is generally a bad idea and gives me nightmares of old C structures. Here is the reason that you should use set/get methods:

1. Debugging - Try and trace a variable every time it is set when the variables are public. Wonder why you can't figure where it is going wrong? Adding 100 break points? Using set/get here can save hours of debugging.

2. No loss of Speed - most compilers will optomize your set/get functions if they are inline, so there is no performance penalty (atleast for c++).

3. Maintainance - Suppose that when data member A is updated, now a count needs to be kept. Using a setter function allows you to change code in one 1 place. Also, suppose a variable type changes from an int to a double. You can still keep around the integer setters/getters for older classes and use new accessor for the new methods for objects that need it.

From the article, its not that setters/getters are bad themselves, but that overuse of them is bad. Here is the key quote: Don't ask for the information you need to do the work; ask the object that has the information to do the work for you.

Another pompous "expert"?

[Anonymous Coward]

Before perusing this discussion, you may want to get some perspective by reading Unskilled and Unaware of It: How Difficulties in Recognizing One's Own Incompetence Lead to Inflated Self-Assessments by Justin Kruger and David Dunning (Journal of Personality and Social Psychology,

Well, I didn't know much about this guy. But anybody who defends his position by referring to this psychology paper doesn't score too high in my book. If you're not familiar with the paper, it basically asserts that stupid people don't realize how stupid they are. So referring to this paper is a subtle way of saying "you're stupid, and you don't know it".

But I'll give him the benefit of the doubt.. after all some other pompous experts have referred to that paper yet raise important points based on sound theory. I.e., there is not necessarily a correlation between being an assmunch and being *wrong*.

So now I read his papers on getters/setters and he claims this is "bad" because it assumes an implementation of the underlying value:

double orderTotal;
Money amount = ...;
//...
orderTotal += amount.getValue(); // orderTotal must be in dollars

Excuse me but having to declare orderTotal to be any particular type is a *JAVA* thing, and not universal to OO programming. In Ruby for instance:

orderTotal += amount.value

No types or assumptions here. Since Ruby is fully OO, this will work even if amount.value returns a Fixnum, a Float, or a SomethingElseEntirely.

He says a "better" way is:

total.increaseBy(amount );

But this is just syntax. In Ruby I would just write:

total += amount

And it doesn't matter what the types (classes) are.

Poor guy is stuck in a statically typed Java hell, with distinctions between primitive types and objects, of course he's gonna think getters/setters are evil and he's gonna become obsessed with keeping his data hidden in a box or behind opaque methods! I can just imagine his code filled with thousands of builder objects with 2-3 levels of abstraction .. and it will just be a grotesque simulation of a true dynamic language in the end, with everything completely decoupled.

I don't know if I should bother reading any more of his writings since I don't use Java.... is the rest of his work "how to get around Java's shortcomings" or is there something a general purpose OO practitioner might find useful???

Intuitive

[roman_mir]

I didn't find it in many programmers I worked with, but personally I find all of the advices in this book intuitive. What I did find in many programmers is the rigidness they assume when someone questions their position on some specifics. I remember a few conversations I had where I questioned the entire OO paradigm, the people look at you as if you are mad.

But the reason why I questioned the OO paradigm was not the paradigm in its purity, but the implementations that I so often saw in real life. Some of the architectural designs that I witnessed did not make any sense and were artificially created to be more complex than the problem at hand required. What is worse, I have seen 'architects' who got into those positions without any merit. I have witnessed architects who think their position is justified because they spend another 4 weeks in the beginning of every project 'rethinking' the ACLs. I have witnessed an 'architect' that was supposed to design a system, but who instead sat down with a programmer, did a bunch of handwaving, and left the programmer without any idea and without documentation on how things are supposed to be done, and it was not a simple thing for that guy who was still a beginner. I cannot count the number of times where I (as a contractor) in different companies was put into a position where I had to solve the problems created by these 'architects' as well as by 'managers' and the marketting people.

Yes, I remember having a conversation about getters, setters about 4 years ago, I was convinced that those things are a horrid idea as well as extends (for almost the same reasons given in the article). I was attacked on more than just the techno-level. It is hard, it is not easy at all to work around bad design decisions, where someone just does something because it is either a pattern they read, or the marketting says it has to be done that way because there was this meeting with an IBM guy, who bought all the managers year-long golf memberships.

What I appreciate in people is the ability to think for themselves and to make decisions on when something is appropriate. I am also a realist, I know that noone on this planet can be perfect 100% of the time. We get tired, we have schedules, we just want to do things fast and dirty, we resist structure because it is easier that way. But those of us who are good enjoy going through all of this nonsense and figuring out sensible ways to still deliver a good system.