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How Design Patterns Solve Design Problems . 23 .. With this book, the Gang of Four have made a seminalcontribution to software engineering . edsebooks/ebooks/Design Patterns, Elements of Reusable Object-Oriented tetraedge.info Find file Copy path. erbicca primeiro commit a0eef73 on Jul 1, . Branch: master. ASD/ASD/Docs&books/Design-patterns-elements-of-reusable- object-oriented-software-Erich-Gamma-Richard-Helm(tetraedge.info).epub.


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The GoF Design Patterns Reference presents the up-to-date version of the standard GoF design patterns in a compact and memory friendly way so that they can. Gang of Four Design Patterns pdf - Download as PDF File .pdf), Text File .txt ) or read online. Programming Patterns. Design Patterns: Elements of Reusable Object-Oriented Software (Addison- Wesley Professional Computing Series) eBook: Erich Gamma, Richard Helm, Ralph.

Capturing a wealth of experience about the design of object-oriented software, four top-notch designers present a catalog of simple and succinct solutions to commonly occurring design problems. Previously undocumented, these 23 patterns allow designers to create more flexible, elegant, and ultimately reusable designs without having to rediscover the design solutions themselves. The authors begin by describing what patterns are and how they can help you design object-oriented software. They then go on to systematically name, explain, evaluate, and catalog recurring designs in object-oriented systems. With Design Patterns as your guide, you will learn how these important patterns fit into the software development process, and how you can leverage them to solve your own design problems most efficiently.

Eric Freeman. The Robert C. Robert C. The Pragmatic Programmer: From Journeyman to Master. Andrew Hunt. Martin Fowler. Clean Code: Product description Amazon. This book isn't an introduction to object-oriented technology or design. See all Product description. Product details Format: Would you like to tell us about a lower price?

Customers who viewed this item also viewed. The Gang of Four. Peeling Design Patterns: Narasimha Karumanchi. Patterns of Enterprise Application Architecture: Frank Buschmann. Share your thoughts with other customers. Write a product review. Customer images. See all customer images. Read reviews that mention design patterns object oriented must read print quality page quality quality of the book looks like book is very good best book book on design pages examples java software developer edition pearson poor reference thin.

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Paperback Verified Purchase. Same as most reviewers I got cheap and faulty copy with only pages. Noticed it very late, one cannot expect to check each n every page of book. Now that replacement window is over I am stuck with faulty copy.

Received and duplicate pre-owned product with poor print quality. The book i received has previous owners name. Great revised edition. Everything is explained in a simple manner which makes it possible for even beginners to pick it up fast. The print is not original. It does not at all looks like a original Pearson print. The print is low quality. The book looks used with crease by the side. The book I received looks like a fake print although it seems to have all the content and should suffice my learning requirements.

Papers used in the book is very thin and does not feel good also the print quality isn't well. The review is only for the physical product, but content wise the book is really good. I know this book is very good for understanding Design Patterns. Amazon's delivery on time is exceptionally good as it does everytime. Book is in good condition except some small marks in some papers. Real life or real-world examples and comparisons like when should we use which structure could have made the book much better.

See all 86 reviews. Would you like to see more reviews about this item? Go to Amazon. Back to top. Get to Know Us. Enhanced Typesetting: Page Flip: Here an elegant. Thread safety is guaranteed by the compiler. The Singleton pattern simply uses a private constructor and a static readonly instance variable that is lazily initialized.

Server lists are created using collection initialization. Only a single instance the singleton of the class should ever exist because servers may dynamically come on-line or off-line. NET specific solution is offered. Server instances are created using object initialization. The Server class has automatic properties.

In addition. The responsibilities of these objects often require that there be just one instance of the class. Page 23 of Other areas in the application rely on these special objects and they need a way to find them. A Singleton removes the need to constantly create and destroy objects. Using the Singleton pattern you centralize authority over a particular resource in a single object.

A common scenario is when you have a stateless object that is created over and over again. Global variables are frowned upon as a bad coding practice. An example follows: This is where the Singleton design pattern comes in.

Using Singleton you can hold one or more global variables and this can be really handy. The intent of the Singleton pattern is to ensure that a class has only one instance and to provide a global point of access to this instance. Other reasons quoted for using Singletons are to improve performance. Be careful though as the Singleton may not be the best solution in this scenario.

One of the activation modes of server objects is called Singleton and their behavior is in line with the GoF pattern definition. NET Framework uses the Singleton pattern is with.

Page 24 of NET Remoting when launching server-activated objects. NET Framework An example where the. Definition Convert the interface of a class into another interface clients expect.

Adapter lets classes work together that couldn't otherwise because of incompatible interfaces. Structural sample code The structural code demonstrates the Adapter pattern which maps the interface of one class onto another so that they can work together. These incompatible classes may come from different libraries or frameworks. Real-world sample code The real-world code demonstrates the use of a legacy chemical databank.

Chemical compound objects access the databank through an Adapter interface. NET optimized code demonstrates the same code as above but uses more modern, built-in. This will allow the derived class to access these variables via properties rather than directly.

Finally, two enumerations Chemical and State were added for increased type safety. NET developers write classes that expose methods that are called by clients.

Most of the time they will be able to control the interfaces, but there are situations, for example, when using 3rd party libraries, where they may not be able to do so. The 3 rd party library performs the desired services but the interface methods and property names are different from what the client expects.

This is a scenario where you would use the Adapter pattern. The Adapter provides an interface the client expects using the services of a class with a different interface. Adapters are commonly used in programming environments where new components or new applications need to be integrated and work together with existing programming components.

Adapters are also useful in refactoring scenarios. Say, you have two classes that perform similar functions but have different interfaces. The client uses both classes, but the code would be far cleaner and simpler to understand if they would share the same interface. You cannot alter the interface, but you can shield the differences by using an Adapter which allows the client to communicate via a common interface.

The Adapter handles the mapping between the shared interface and the original interfaces. Adapter in the. NET Framework The. NET Framework uses the Adapter pattern extensively by providing the ability for.

As you know, there are significant differences between COM and. NET expects an Exception to be thrown in case of an error.

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The Adapter adapts the COM interface to what. NET clients expect. Bridge Definition Decouple an abstraction from its implementation so that the two can vary independently. Page 29 of The implementation can evolve without changing clients which use the abstraction of the object. Page 30 of The DataObject implementations can evolve dynamically without changing any clients. Typically the Implementation interface provides only primitive operations.

The DataObject abstract class has been replaced by an interface because DataObject contains no implementation code. Structural Real-world sample code The real-world code demonstrates the Bridge pattern in which a BusinessObject abstraction is decoupled from the implementation in DataObject. This interface doesn't have to correspond exactly to Abstraction's interface.

Structural sample code The structural code demonstrates the Bridge pattern which separates decouples the interface from its implementation. Applications that rely on these drivers are abstractions that work with any database SQL Server. The ODBC architecture decouples an abstraction from its implementation so that the two can vary independently — the Bridge pattern in action.

The overall system. The abstraction decouples the client. Most developers are not aware of this. NET Framework Bridge is a high-level architectural pattern and as such is not exposed by the. NET libraries themselves. A Bridge pattern is created by moving a set of abstract operations to an interface so that both the client and the service can vary independently. A classic example of the Bridge pattern is when coding against device drivers. Interestingly enough. Bridge in the.

If you build an application that uses a driver to communicate with a database. It is important to realize that the client application is the abstraction. NetOptimized Bridge: A driver is an object that independently operates a computer system or external hardware device. Page 31 of Bridge is a high-level architectural patterns and its main goal is through abstraction to help. NET developers write better code. Composite Definition Compose objects into tree structures to represent part-whole hierarchies.

Page 32 of Composite lets clients treat individual objects and compositions of objects uniformly. Leaf PrimitiveElement o o represents leaf objects in the composition. Page 33 of Structural sample code The structural code demonstrates the Composite pattern which allows the creation of a tree structure in which individual nodes are accessed uniformly whether they are leaf nodes or branch composite nodes.

Structural Real-world sample code The real-world code demonstrates the Composite pattern used in building a graphical tree structure made up of primitive nodes lines. A leaf has no children.

The composite pattern is a great candidate for generics and you will find these used throughout this example. Forms namespace and the other for ASP.

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NET apps in the System. Page 34 of Composite in the. This code demonstrates much of the power that generics offer to. Numerous interesting language features are used in this example. This is an open type which has the ability to accept any type parameter.

This common interface greatly facilitates the design and construction of recursive algorithms that iterate over each object in the Composite collection. All nodes in the Composite pattern share a common interface which supports individual items as well as groups of items.

The class named Shape does implement this generic interface so that comparisons can be made between shape objects. UI namespace. NetOptimized Composite: The nodes of the tree either contain an individual object leaf node or a group of objects a subtree of nodes. It is used like any other collection. A tree control is a good example of a Composite pattern. NET developers.

Examples are the two Control classes one for Windows apps in the System. This facilitates the process of adding and removing shapes from the list of tree nodes. Page 35 of WPF also has many built-in controls that are Composites.

NET framework. The built-in. Page 36 of Decorators provide a flexible alternative to subclassing for extending functionality. Decorator Definition Attach additional responsibilities to an object dynamically. ConcreteComponent Book. A NET 3. Page 37 of NET optimized code demonstrates an example of the Decorator design pattern that uses generics.

Decorator Decorator maintains a reference to a Component object and defines an interface that conforms to Component's interface. ConcreteDecorator Borrowable o adds responsibilities to the component. Structural Real-world sample code The real-world code demonstrates the Decorator pattern in which 'borrowable' functionality is added to existing library items books and videos.

NetOptimized Decorator: Structural sample code The structural code demonstrates the Decorator pattern which dynamically adds extra functionality to an existing object. It is polymorphic with the original class so that clients can invoke it just like the original class.

Flush and others.

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Decorator classes usually have a constructor with an argument that represents the class they intent to decorate: The Stream class is an abstract class that reads or writes a sequence of bytes from an IO device disk. Decoration is a flexible technique because it takes place at runtime. Page 38 of The BufferedStream class is a Decorator that wraps the Stream class and reads and writes large chunks of bytes for better performance.

Decorator in the. NET Framework include a set of classes that are designed around the Stream class. In most cases. As an aside. Subsystem classes Bank. Page 39 of Loan implement subsystem functionality. Facade Definition Provide a unified interface to a set of interfaces in a subsystem. Structural Real-world sample code The real-world code demonstrates the Facade pattern as a MortgageApplication object which provides a simplified interface to a large subsystem of classes measuring the creditworthiness of an applicant.

NET optimized sample code This code is essentially the same as the real-world example. Structural sample code The structural code demonstrates the Facade pattern which provides a simplified and uniform interface to a large subsystem of classes. The only difference is the use of. Page 40 of NET Framework In the. Calls into the business layer take place via a well defined service layer.

To discuss this properly we need to distinguish high-level architectural Facades from lower level component type facades. This service layer. It exposes a simple API to the client. In a 3-tier application the presentation layer is the client. Page 41 of Facade in the. Facades themselves are often implemented as singleton abstract factories. An example of an aggregate component is System. It is used in scenarios where there is a need to present a simplified view over more complex set of types.

Complex operations. Facades may reduce the expressiveness of the API. WebClient which provides a high-level interface for sending and retrieving data from a network resources identified by a general URI.

MessageQueue which provides access to a queue on a Message Queue server. NET Framework libraries are no exception. SmtpMail to send mail messages. Page 42 of SerialPort which is a powerful serial port class. NET developer can see. The objective of the. A ConcreteFlyweight object must be sharable. Any state it stores must be intrinsic. All rights reserved Page 43 of CharacterZ o implements the Flyweight interface and adds storage for intrinsic state.

ConcreteFlyweight CharacterA. Flyweigth Definition Use sharing to support large numbers of fine-grained objects efficiently. Page 44 of When a client requests a flyweight. Structural sample code The structural code demonstrates the Flyweight pattern in which a relatively small number of objects is shared many times by different clients.

It is common for UnsharedConcreteFlyweight objects to have ConcreteFlyweight objects as children at some level in the flyweight object structure as the Row and Column classes have. Structural Real-world sample code The real-world code demonstrates the Flyweight pattern in which a relatively small number of Character objects is shared many times by a document that has potentially many characters.

The Flyweight interface enables sharing. Shared flyweight objects are immutable. Page 45 of Flyweight in the. Examples include. The stateless flyweights refer to the same memory location that holds the immutable string. NET Framework as a string management technique to minimize memory usage for immutable strings. NET uses Flyweights for strings that are declared at compile time and have the same sequence of characters.

NetOptimized Flyweight: They are rarely used in data-driven business type applications. You will find flyweights mostly in utility type applications word processors. Flyweights are usually combined with the Factory pattern as demonstrated in the. NET optimized code uses a generic Dictionary collection to hold and quickly access Flyweight Character objects in memory.

NET Optimized code sample. NET Framework As mentioned above. The generic collection increases the type-safety of the code.

GoF Design Patterns Reference

Flyweights are used internally in the. Proxy Definition Provide a surrogate or placeholder for another object to control access to it. Page 46 of Proxy may refer to a Subject if the RealSubject and Subject interfaces are the same.

Structural sample code The structural code demonstrates the Proxy pattern which provides a representative object proxy that controls access to another similar object.

This code demonstrates the Remote Proxy pattern which provides a representative object i. Page 47 of Structural Real-world sample code The real-world code demonstrates the Proxy pattern for a Math object represented by a MathProxy object. Page 48 of NetOptimized Proxy: The Proxy forwards the request to a target object.

The interface of the Proxy object is the same as the original object and clients may not even be aware they are dealing with a proxy rather than the real object. Typically this occurs when there is a dependency on a remote resource a call to another computer for example or when an object takes a long time to load.

The proxy pattern is meant to provide a surrogate or placeholder for another object to control access to it. A Smart Reference is a proxy for a pointer. Clients of these objects expect this work to be done quickly and efficiently. There are 3 different types of proxies: As is common with proxies. Page 49 of NET Framework In. NET the Proxy pattern manifests itself in the Remoting infrastructure.

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Clients of WCF services also rely heavily on auto-generated proxy objects. NET Remoting. Chain or Responsibility Definition Avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request. President handles requests it is responsible for can access its successor if the ConcreteHandler can handle the request.

Chain the receiving objects and pass the request along the chain until an object handles it. Page 50 of Structural Real-world sample code The real-world code demonstrates the Chain of Responsibility pattern in which several linked managers and executives can respond to a purchase request or hand it off to a superior. Page 51 of The Purchase and other classes use. The Successor settings are simplified by using properties. Each position has can have its own set of rules which orders they can approve.

The chain of responsibility pattern is frequently used in the Windows event model in which a UI control can either handle an event for example a mouse click or let it fall through to the next control in the event chain. The delegates are implemented using generics in which event handlers are type safe and not restricted to senders of type object but rather to types that are appropriate for the event — in the sample code type Approver see.

NET you can identify a Chain of Responsibility in the Windows event model where each UI control can decide to process an event or let it fall through to the next control in the event chain.

Note that Chain-of-Responsibility is not commonly used in business application development. Page 52 of This search is usually modeled according to the specific needs of the application domain. NET Remoting in which a message between a client and a server passes through one or more so-called message sinks. Occasionally you may run into a Chain of Responsibility implementation in which a chain of objects process a message between a sender and a receiver.

Message sinks form a chain as each sink has a reference to the next sink in the chain. The Chain of Responsibility design pattern offers an opportunity to build a collection of loosely coupled objects by relieving a client from having to know which objects in a collection can satisfy a request by arranging these objects in a chain.

This pattern requires a way to order the search for an object that can handle the request. NetOptimized Chain of Responsibility: Loosely coupled objects have the advantage that they are easier to maintain and easier to change compared to systems where there is tight coupling between objects i. This is slightly different from the GoF definition in which just one object in a chain decides to handle the request. Chain of Responsibility in the. Command Definition Encapsulate a request as an object.

Page 53 of Structural sample code The structural code demonstrates the Command pattern which stores requests as objects allowing clients to execute or playback the requests. Prefixing it with ' ' allows using it as an identifier. In this example the abstract Command class has been replaced by the ICommand interface because the abstract class had no implementation code at all.

Structural Real-world sample code The real-world code demonstrates the Command pattern used in a simple calculator with unlimited number of undo's and redo's. Page 54 of Note that in C the word 'operator' is a keyword.

We would have expected that the Command pattern would be exposed in. The classic usage of this pattern is a menu system where each command object represents an action and an associated undo action.

NET as part of a unified WinForms command routing architecture. Page 55 of Menu actions include menu items such as File Open. All Commands implement the same interface. Edit Copy. Areas where you find Command patterns are: Typically their interface includes methods such as Do and Undo or Execute and Undo.

Command in the. File Save. OneExpression o o implements an Interpret operation associated with terminal symbols in the grammar.

Page 56 of Interpreter Definition Given a language. Page 57 of The abstract syntax tree is assembled from instances of the NonterminalExpression and TerminalExpression classes o invokes the Interpret operation Structural sample code The structural code demonstrates the Interpreter patterns. Interpret typically calls itself recursively on the variables representing R1 through Rn. All rights reserved.. Structural Real-world sample code The real-world code demonstrates the Interpreter pattern which is used to convert a Roman numeral to a decimal.

Rn in the grammar maintains instance variables of type AbstractExpression for each of the symbols R1 through Rn. Certain types of problems lend themselves to be characterized by a language. Grammars are usually hierarchical tree-like structures that step through multiple levels but end up with terminal nodes also called literals. For an example visit: This type of problem. VBScript comes to mind. The well-known Towers of Hanoi puzzle is an example of the type of problem that can be encoded by a simple grammar and implemented using the Interpreter design pattern.

The truth is that if you really need this type of control it is probably easier and faster to use an existing command interpreter or expression evaluator tool out of the box. The Interpreter design pattern solves this particular problem — that of creating a scripting language that allows the end user to customize their solution. This language describes the problem domain which should be well-understood and welldefined.

Here the abstract classes have been replaced by interfaces because the abstract classes have no implementation code.

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NET Dynamic Languages. Page 58 of NetOptimized Interpreter: NET Framework libraries. Interpreter in the. Page 59 of Just like State and Strategy. It also has similarities with the Composite pattern. Page 60 of Iterator Definition Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation. ConcreteIterator Iterator implements the Iterator interface.

C offers built-in iterator support with the yield return keyword which makes implementing the IEnumerable and IEnumerator interfaces even easier even iterating over trees and other more complex data structures. Page 61 of NET's built-in generic Iterator design pattern.

Structural Real-world sample code The real-world code demonstrates the Iterator pattern which is used to iterate over a collection of items and skip a specific number of items each iteration. In this example the IEnumerable and IEnumerator interfaces are implemented using. Two looping methods are demonstrated: While and For Each. NET libraries. The Iterator design pattern solves this problem by separating the collection of objects from the traversal of these objects by implementing a specialized iterator class.

Page 62 of Both languages have a built-in construct that facilitates iterating over collections: Not only do you find the Iterator design pattern deep into the. NetOptimized Iterator: These collections may be stored as an array. WriteLine vote. Page 63 of Page 64 of Mediator promotes loose coupling by keeping objects from referring to each other explicitly. Mediator Definition Define an object that encapsulates how a set of objects interact.

Page 65 of The Chatroom is the central hub through which all communication takes place. At this point only one-to-one communication is implemented in the Chatroom. Here the abstract classes have been replaced with interfaces because there is no implementation code.

NetOptimized Mediator: The mediator is a central hub through which all interaction must take place. Structural Real-world sample code The real-world code demonstrates the Mediator pattern facilitating loosely coupled communication between different Participants registering with a Chatroom.

Page 66 of Mediator in the. When selecting custom options for your computer. Another area where Mediator is used is in complex configuration scenarios.

For example a particular graphics card may not work with a Sony monitor. The Mediator is the pattern that flags these kinds of incompatibilities. Take for example a dialog in which you enter options to make a flight reservation. A simple Mediator rule would be: Mediator patterns are frequently used in the development of complex dialog boxes. Its main role is to determine whether a particular combination of hardware components work together or not. Page 67 of The memento may store as much or as little of the originator's internal state as necessary at its originator's discretion.

Caretaker sees a narrow interface to the Memento -. Mementos have effectively two interfaces. Memento Definition Without violating encapsulation. Structural Real-world sample code The real-world code demonstrates the Memento pattern which temporarily saves and then restores the SalesProspect's internal state Code in project: Note that this approach is not necessarily the most efficient because of the relatively expensive serialization and deserialization steps.

In this example the Memento is more general. The Originator class is decorated with the Serializable attribute. Page 68 of Structural sample code The structural code demonstrates the Memento pattern which temporary saves and restores another object's internal state Code in project: It will take any serializable object and save and restore it.

Deserialization is the process of taking in stored information and recreating objects from it. Storage options include memory for example Session. Memento in the. NET Framework Serialization is the process of converting an object into a linear sequence of bytes for either storage or transmission to another location.

NET offers and therefore qualifies as an example of Memento in the. Page 69 of Scenarios in which you may want to restore an object into a state that existed previously include: In an abstract sense you can view a database as an implementation of the Memento design pattern. This is what the serialization architecture of.

Any number of Observer objects may observe a subject provides an interface for attaching and detaching Observer objects. Observer Definition Define a one-to-many dependency between objects so that when one object changes state. Structural Real-world sample code The real-world code demonstrates the Observer pattern in which registered investors are notified every time a stock changes value Code in project: Page 71 of NET multicast delegates which are an implementation of the Observer pattern.

Generic delegates allow for event handler-specific arguments. Delegates are type safe function pointers that have the ability to call a method.