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

Re:Getters/setters bad?

[Misch]

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

My guess is that in some instances, publically accessible getter/setter methods can be construed to be "exposing the underlying implementation" of a class. Of course, that just means you need to judiciously use getter and setter methods.

That's my guess at least. I suppose I should read the book.

Re:Getters/setters bad?

[emiddlec]

The article Why getter and setter methods are evil (from above) includes the following:

1. A fundamental precept of OO systems is that an object should not expose any of its implementation details. This way, you can change the implementation without changing the code that uses the object. It follows then that in OO systems you should avoid getter and setter functions since they mostly provide access to implementation details.

Apparently the argument against getter / setter functions goes..

1. OO systems should not expose implementation
2. Getter and setter functions mostly expose access to implementation details
3. Therefore, OO systems should avoid getter and setter functions

While the logic is sound, I think that item #2 is debatable.. If you design an object and mindlessly add get/set functions for every piece of private data in the object, then you're probably guilty of exposing the implementation. But if you design the object's public interface first, and decide on the private data afterwards, I would guess that you're probably in the clear to have used get/set functions "correctly." IMO it's not the functions themselves that are the problem, but rather the adherence to correct design principles.

Should be titled "Holub on Java Patterns"

[pammon]

The dirty unacknowledged secret of design patterns is that they're strongly coupled to a language. For example, switching from a statically typed language like Java to a dynamic one with forwarding substantially changes the approach to Factory, Proxy, Singleton, Observer and others. In fact, they're often rendered trivial. The claim that the approaches described in the book apply to any language is just not true. These patterns are for Java and Java-like languages.

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.