Excellent book, everything is explained in detail and presented in a user-friendly manner. Special thanks for supporting multiple formats and providing the readers with the ability to read the book on the go. I would like to note right away that the book is beautifully illustrated The information about SOLID, and in particular, about the principle of Barbara Liskov, is presented very well and in a user-friendly manner. I found some new information for myself about the private members of the base classes and the fact that you explicitly separate the restrictions on preconditions by type and attribute values.
It is really easier to figure everything out this way. The book is great. Excellent illustrations and examples. I am now preparing a report on Design Patterns at work. Everything that is explained using cats is always clear, and the more allegories the better.
I haven't finished the book yet, but the first impression is rather good, thank you! I confirm that I bought this book, and am satisfied with the purchase, otherwise I would not have bought it :. I was looking to find some information on the most widely used patterns builder and factory , and I ended up finding the materials on the website. Your website is by far the BEST of all that I have come across on this topic, and that's why I bookmarked it and added the PDF version to the offline library on my tablet.
I almost finished reading the book. I will say right away that I liked it; the book offers real-life examples, the descriptions and the pseudocode are good. The material is interesting, even though it was a bit unusual to learn on examples with pseudocode. For pros, this approach is, of course, quite acceptable.
In general, the book is definitely worth its price. An ebook in human-friendly, natural language. Written with minimal jargon and technicalese, maximal code samples and illustrations.
Not bound to a specific programming language. Code examples are in pseudocode, applicable to most modern OOP languages. Readable on any device. The eBook is available in four formats:. Always handy and searchable. The ebook is a convenient reference guide. Unlike a paperback, it is searchable and impossible to leave behind somewhere. Pleasant reading when commuting or relaxing. Where else can you learn in peace these days, if not during flights and on the bus or subway?
Well, maybe in bed…. Easy reading day or night. Good news for night owls! The eBook looks great on a light background for day-reading or a dark one for night-reading. Send us a forum message or email support refactoring. We usually respond within a few hours. Hey, I have just reduced the price for all products. Check it out ». Buy as a gift Buy for my team. Open in browser Download PDF. Satisfaction guaranteed Risk nothing by buying now. Your personalized copy of Dive Into Design Patterns pages of great technical writing !
What others say? Facebook Add a review. I think what you have currently is well done and the organization is superb! All and all I give your book a solid 5 stars. No suggestion as of now I am still in between and I am happy with my purchase. Overall, thank you very much for the high-quality material. The author did a great job creating this book. Note: the book is supplied with C examples since spring, Thank you for your work, and good luck in your endeavors!
Note: the book is now supplied with PHP and Python examples. I liked the book; from time to time I apply the solutions from the book in my work.
I'm pleased with the book and very thankful for your work. It seemed strange that the book is over 30mb, though. What can be added: examples with Anti-Patterns, what not to do. I do really enjoy your book. And would like to buy printed version to have it on my work place. I confirm that I bought this book, and am satisfied with the purchase, otherwise I would not have bought it : I was looking to find some information on the most widely used patterns builder and factory , and I ended up finding the materials on the website.
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Communicate better with colleagues. Just share the name of the pattern rather than wasting an hour explaining the details of your cool design and its classes to other programmers. Get the glory without the sweat. Pattern Beginners. If you have never studied patterns, the book explains the basic principles of object-oriented programming with real-life examples. Before diving into the patterns, we look at the design values and principles on which the patterns are built.
Pattern Refreshers. If you studied patterns a while ago, but have forgotten things, the ebook can refresh your memory as serve as a handy reference.
Quickly find sections of interest without having to read it from start to finish. Language Switchers. Check out the quality of the book for yourself. The demo includes the table of contents, several introductory chapters, three design principles, and the Factory Method design pattern.
Risk nothing by buying now. If within a month of purchase you decide that the book is not helpful, all your money will be returned.
No questions asked. The only improvement I see is making printed version available I prefer paper to pdf and maybe in another languages french, spanish, chinese? Your book is great. I am junior level developer and certainly happy with the purchase!
I like the structure of how each pattern is presented, and the UML and examples really clarify things. I also like the "vibe", which keeps it fun yet on-point. I can't think of a con. Thanks for this! The book is awesome, easy-understanding and well-written. Just have a little suggestion to organize the content not in alphabetical order but by categories would be better. And also put some code in it [rather than having it in separate archive] so that it would be easier to read on an iPad when travel.
I read it the same day I got it, I mostly use it as a refresher on on when I dont see the woods for the trees. I think it's fine the way it is. I have been really busy with work recently. The info you have on design patterns has been a huge help and an excellent reference! I only had time to glance at the book but it seems really amazing. I hope to have time since next month to read it.
About the things that made me to buy it are the cartoons and UML diagrams that simplifies the understanding of each pattern. I really like them! I would like to suggest you to do something similar including cartoons with the most famous programming antipatterns.
I have just read the book and I think it is amazing. I have bought both of your patterns books and refactoring course and if you need me to buy from you again I will :. I wish you could have the code written in Java. I am loving the book so far. I'm currently reading it on my Kindle. I'll use it to make dojos with some friends of mine so that we practice the principles of the book.
As for suggestions, maybe it's a bit too soon to say since I'm still at the beginning and I'm a slow reader, but maybe exercises? I don't even know if the book presents exercises. Maybe it does and I didn't get there yet. The book is great and makes all the patterns more easier to understand than the books or examples i found on the internet. You are going from the problem to the solution and that process give me the best understanding about pattern. Comparations betweem patterns are helpful alot.
Maybe the UML diagrams should have cardinality and the role that a class plays in the relationship because it's difficult for the first reading for every problem follow all properties from the code or from the text. Maybe for some patters you should use the same problem, saving time to understand the new problem but to concentrate just on pattern, and make good comparision of new pattern with the old one. Well it's good to have more different problems for diversity but it's more time consuming and little blury the pattern.
I have already started reading the book, though I'm not quite half way yet. My impressions so far is that I like it! I enjoy the UML diagrams high diagrams explaining the connections and the coding examples. I also appreciate the explanation on when to use a particular pattern and what are it's strengths and weaknesses. There is a lot of good information and I have been re-reading sections to make sure I have a firm understanding as to why a particular pattern is beneficial and how to properly implement it before moving on.
The book is great! I discovered your site a few months ago in my ongoing quest to design better code. I'm a big fan of the illustrations - they're funny and do a good job of illustrating the concepts. I'm a long-term user of your website refactoring.
I have to say the website refactor. It's the for me to learn how to improve my code in a higher level than just learning grammars and best practices of programming languages. Although I've purchased the old Design Patterns book long before and put it on my bookshelf, I seldom read it. In this case, you can use a different builder each time you produce something with the director. The example of step-by-step construction of cars and the user guides that fit those car models.
A car is a complex object that can be constructed in a hundred different ways. This class has a set of methods for configuring various parts of a car. If the client code needs to assemble a special, fine-tuned model of a car, it can work with the builder directly.
On the other hand, the client can delegate the assembly to the director class, which knows how to use a builder to construct several of the most popular models of cars. You might be shocked, but every car needs a manual seriously, who reads them?
The manual describes every feature of the car, so the details in the manuals vary across the different models. This class implements the same building methods as its car-building sibling, but instead of crafting car parts, it describes them.
By passing these builders to the same director object, we can construct either a car or a manual. The final part is fetching the resulting object. A metal car and a paper manual, although related, are still very different things.
Hence, we obtain the result of the construction from the builder which performed the job. Calling such a beast is very inconvenient; therefore, you overload the constructor and create several shorter versions with fewer parameters. These constructors still refer to the main one, passing some default values into any omitted parameters. Creating such a monster is only possible in languages that support method overloading, such as C or Java. The Builder pattern lets you build objects step by step, using only those steps that you really need.
The base builder interface defines all possible construction steps, and concrete builders implement these steps to construct particular representations of the product. Meanwhile, the director class guides the order of construction. You could defer execution of some steps without breaking the final product. You can even call steps recursively, which comes in handy when you need to build an object tree. This prevents the client code from fetching an incomplete result.
Make sure that you can clearly define the common construction steps for building all available product representations. Declare these steps in the base builder interface. Create a concrete builder class for each of the product representations and implement their construction steps. Think about creating a director class. It may encapsulate various ways to construct a product using the same builder object.
The client code creates both the builder and the director objects. Before construction starts, the client must pass a builder object to the director. The director uses the builder object in all further construction.
The construction result can be obtained directly from the director only if all products follow the same interface. Otherwise, the client should fetch the result from the builder. You can isolate complex construction code from the business logic of the product. How would you do it? First, you have to create a new object of the same class.
Then you have to go through all the fields of the original object and copy their values over to the new object. The pattern declares a common interface for all objects that support cloning. This interface lets you clone an object without coupling your code to the class of that object.
Usually, such an interface contains just a single clone method. The implementation of the clone method is very similar in all classes. The method creates an object of the current class and carries over all of the field values of the old object into the new one. You can even copy private fields because most programming languages let objects access private fields of other objects that belong to the same class. Pre-built prototypes can be an alternative to subclassing. When your objects have dozens of fields and hundreds of possible configurations, cloning them might serve as an alternative to subclassing.
The division of a cell. After mitotic division, a pair of identical cells is formed. The original cell acts as a prototype and takes an active role in creating the copy. The Prototype interface declares the cloning methods. The Concrete Prototype class implements the cloning method.
The Client can produce a copy of any object that follows the prototype interface. Prototype registry implementation 1.
It stores a set of pre-built objects that are ready to be copied. However, if you need better search criteria than a simple name, you can build a much more robust version of the registry. Cloning a set of objects that belong to a class hierarchy. All shape classes follow the same interface, which provides a cloning method.
X 16 this. Y 17 this. The Prototype pattern provides the client code with a general interface for working with all objects that support cloning.
This interface makes the client code independent from the concrete classes of objects that it clones. Somebody could have created these subclasses to be able to create objects with a specific configuration. Instead of instantiating a subclass that matches some configuration, the client can simply look for an appropriate prototype and clone it. Create the prototype interface and declare the clone method in it. Or just add the method to all classes of an existing class hierarchy, if you have one.
A prototype class must define the alternative constructor that accepts an object of that class as an argument. The constructor must copy the values of all fields defined in the class from the passed object into the newly created instance. The constructor is a more convenient place to do this because it delivers the resulting object right after you call the new operator.
The cloning method usually consists of just one line: running a new operator with the prototypical version of the constructor. Note, that every class must explicitly override the cloning method and use its own class name along with the new operator. Otherwise, the cloning method may produce an object of a parent class.
Optionally, create a centralized prototype registry to store a catalog of frequently used prototypes. This method should search for a prototype based on search criteria that the client code passes to the method. The criteria might either be a simple string tag or a complex set of search parameters. After the appropriate prototype is found, the registry should clone it and return the copy to the client. Applying the pattern lets you clone complex structures instead of re-constructing them from scratch.
Ensure that a class has just a single instance. Why would anyone want to control how many instances a class has? The most common reason for this is to control access to some shared resource—for example, a database or a file. Note that this behavior is impossible to implement with a regular constructor since a constructor call must always return a new object by design. Remember those global variables that you all right, me used to store some essential objects? Just like a global variable, the Singleton pattern lets you access some object from anywhere in the program.
However, it also protects that instance from being overwritten by other code. Nowadays, the Singleton pattern has become so popular that people may call something a singleton even if it solves just one of the listed problems. All following calls to this method return the cached object. So whenever that method is called, the same object is always returned. A country can have only one official government. Calling the getInstance method should be the only way of getting the Singleton object.
This method caches the first created object and returns it in all subsequent calls. This method either creates a new object or returns an existing one if it has already been created. Nothing, except for the Singleton class itself, can replace the cached instance. Note that you can always adjust this limitation and allow creating any number of Singleton instances. The only piece of code that needs changing is the body of the getInstance method. Add a private static field to the class for storing the singleton instance.
Declare a public static creation method for getting the singleton instance. It should create a new object on its first call and put it into the static field. The method should always return that instance on all subsequent calls.
Make the constructor of the class private. The static method of the class will still be able to call the constructor, but not the other objects. The pattern solves two problems at the time. Since the constructor of the singleton class is private and overriding static methods is impossible in most languages, you will need to think of a creative way to mock the singleton.
But there are two fundamental differences between these patterns: 1. There should be only one Singleton instance, whereas a Flyweight class can have multiple instances with different intrinsic states. The Singleton object can be mutable. Flyweight objects are immutable. The app downloads the stock data from multiple sources in XML format and then displays nice-looking charts and diagrams for the user. At some point, you decide to improve the app by integrating a smart 3rd-party analytics library.
You could change the library to work with XML. However, this might break some existing code that relies on the library. This is a special object that converts the interface of one object so that another object can understand it. An adapter wraps one of the objects to hide the complexity of conversion happening behind the scenes. For example, you can wrap an object that operates in meters and kilometers with an adapter that converts all of the data to imperial units such as feet and miles.
Adapters can not only convert data into various formats but can also help objects with different interfaces collaborate. The adapter gets an interface, compatible with one of the existing objects. Upon receiving a call, the adapter passes the request to the second object, but in a format and order that the second object expects. To solve the dilemma of incompatible formats, you can create XML-to-JSON adapters for every class of the analytics library that your code works with directly.
Then you adjust your code to communicate with the library only via these adapters. When an adapter receives a call, it translates the incoming XML data into a JSON structure and passes the call to the appropriate methods of a wrapped analytics object. The power plug and sockets standards are different in different countries. The problem can be solved by using a power plug adapter that has the American-style socket and the European-style plug. It can be implemented in all popular programming languages.
The Client is a class that contains the existing business logic of the program. The Client Interface describes a protocol that other classes must follow to be able to collaborate with the client code. The Service is some useful class usually 3rd-party or legacy.
The adapter receives calls from the client via the adapter interface and translates them into calls to the wrapped service object in a format it can understand.
Thanks to this, you can introduce new types of adapters into the program without breaking the existing client code. This can be useful when the interface of the service class gets changed or replaced: you can just create a new adapter class without changing the client code.
Class adapter This implementation uses inheritance: the adapter inherits interfaces from both objects at the same time. The adaptation happens within the overridden methods. The resulting adapter can be used in place of an existing client class.
Adapting square pegs to round holes. The much more elegant solution would be to put the missing functionality into an adapter class.
Then you would wrap objects with missing features inside the adapter, gaining needed features dynamically. This approach looks very similar to the Decorator pattern. Declare the client interface and describe how clients communicate with the service.
Create the adapter class and make it follow the client interface. Leave all the methods empty for now. Add a field to the adapter class to store a reference to the service object. One by one, implement all methods of the client interface in the adapter class. The adapter should delegate most of the real work to the service object, handling only the interface or data format conversion.
Clients should use the adapter via the client interface. This will let you change or extend the adapters without affecting the client code. You can separate the interface or data conversion code from the primary business logic of the program. You can introduce new types of adapters into the program without breaking the existing client code, as long as they work with the adapters through the client interface.
On the other hand, Adapter is commonly used with an existing app to make some otherwise-incompatible classes work together nicely. Adapter usually wraps just one object, while Facade works with an entire subsystem of objects. Indeed, all of these patterns are based on composition, which is delegating work to other objects. However, they all solve different problems. It can also communicate to other developers the problem the pattern solves.
Sound scary? Say you have a geometric Shape class with a pair of subclasses: Circle and Square. You want to extend this class hierarchy to incorporate colors, so you plan to create Red and Blue shape subclasses. Number of class combinations grows in geometric progression. Adding new shape types and colors to the hierarchy will grow it exponentially. And after that, adding a new color would require creating three subclasses, one for each shape type. The further we go, the worse it becomes.
The Bridge pattern attempts to solve this problem by switching from inheritance to composition. What this means is that you extract one of the dimensions into a separate class hierarchy, so that the original classes will reference an object of the new hierarchy, instead of having all of its state and behaviors within one class.
You can prevent the explosion of a class hierarchy by transforming it into several related hierarchies. The Shape class then gets a reference field pointing to one of the color objects. Now the shape can delegate any color-related work to the linked color object.
That reference will act as a bridge between the Shape and Color classes. In my opinion, the terms sound too academic and make the pattern seem more complicated than it really is. Abstraction also called interface is a high-level control layer for some entity. It should delegate the work to the implementation layer also called platform. In a worst-case scenario, this app might look like a giant spaghetti bowl, where hundreds of conditionals connect different types of GUI with various APIs all over the code.
Making even a simple change to a monolithic codebase is pretty hard because you must understand the entire thing very well. Making changes to smaller, well-defined modules is much easier. The class hierarchy will grow exponentially because adding a new GUI or supporting a different API would require creating more and more classes.
One of the ways to structure a cross-platform application. The abstraction object controls the appearance of the app, delegating the actual work to the linked implementation object. Moreover, adding support for another operating system only requires creating a subclass in the implementation hierarchy.
The Abstraction provides high-level control logic. It relies on the implementation object to do the actual low-level work. The abstraction may list the same methods as the implementation, but usually the abstraction declares some complex behaviors that rely on a wide variety of primitive operations declared by the implementation. Concrete Implementations contain platform-specific code. Refined Abstractions provide variants of control logic. Like their parent, they work with different implementations via the general implementation interface.
Usually, the Client is only interested in working with the abstraction. The Device classes act as the implementation, whereas the Remote s act as the abstraction.
The base remote control class declares a reference field that links it with a device object. All remotes work with the devices via the general device interface, which lets the same remote support multiple device types. You can develop the remote control classes independently from the device classes. For example, a basic remote control might only have two buttons, but you could extend it with additional features, such as an extra battery or a touchscreen. The changes made to one of the variations of functionality may require making changes across the whole class, which often results in making errors or not addressing some critical side effects.
The Bridge pattern lets you split the monolithic class into several class hierarchies. After this, you can change the classes in each hierarchy independently of the classes in the others. This approach simplifies code maintenance and minimizes the risk of breaking existing code. The original class delegates the related work to the objects belonging to those hierarchies instead of doing everything on its own. By the way, this last item is the main reason why so many people confuse the Bridge with the Strategy pattern.
Remember that a pattern is more than just a certain way to structure your classes. It may also communicate intent and a problem being addressed. Identify the orthogonal dimensions in your classes.
See what operations the client needs and define them in the base abstraction class. Determine the operations available on all platforms.
Declare the ones that the abstraction needs in the general implementation interface. For all platforms in your domain create concrete implementation classes, but make sure they all follow the implementation interface. Inside the abstraction class, add a reference field for the implementation type. If you have several variants of high-level logic, create refined abstractions for each variant by extending the base abstraction class.
After that, the client can forget about the implementation and work only with the abstraction object. You can introduce new abstractions and implementations independently from each other. You can focus on high-level logic in the abstraction and on platform details in the implementation.
Design Patterns for Humans. Coding in Delphi, Nick Hodges. Dependency Injection in Delphi, Nick Hodges. Design Patterns for Humans, Kamran Ahmed. Your code has fewer mistakes because you are using a proven, standard solution covering all hidden problems. Communicate better with colleagues. Just share the name of the pattern rather than wasting an hour explaining the details of your cool design and its classes to other programmers.
Get the glory without the sweat. Who is this book for?
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