Leblanc Bass Clarinet 0 0 8 0 Disc. The document is 'an arrangement of basic graphical elements' such as characters, lines, other shapes, etc.
The structure of the document contains a collection of these elements, and each element can in turn be a substructure of other elements. A recursive composition is a hierarchical structure of elements, that builds 'increasingly complex elements out of simpler ones' pp. Each node in the structure knows of its own children and its parent.
If an operation is to be performed on the whole structure, each node calls the operation on its children recursively. This is an implementation of the composite pattern, which is a collection of nodes. The node is an abstract base class, and derivatives can either be leaves singular , or collections of other nodes which in turn can contain leaves or collection-nodes. When an operation is performed on the parent, that operation is recursively passed down the hierarchy. Formatting differs from structure.
Formatting is a method of constructing a particular instance of the document's physical structure. This includes breaking text into lines, using hyphens, adjusting for margin widths, etc.
A Compositor class will encapsulate the algorithm used to format a composition. Compositor is a subclass of the primitive object of the document's structure. A Compositor has an associated instance of a Composition object.
When a Compositor runs its Compose , it iterates through each element of its associated Composition, and rearranges the structure by inserting Row and Column objects as needed. The Compositor itself is an abstract class, allowing for derivative classes to use different formatting algorithms such as double-spacing, wider margins, etc.
The Strategy Pattern is used to accomplish this goal. A Strategy is a method of encapsulating multiple algorithms to be used based on a changing context. In this case, formatting should be different, depending on whether text, graphics, simple elements, etc. The ability to change the graphical interface that the user uses to interact with the document. The use of a transparent enclosure allows elements that augment the behaviour of composition to be added to a composition.
These elements, such as Border and Scroller, are special subclasses of the singular element itself. This allows the composition to be augmented, effectively adding state-like elements. Since these augmentations are part of the structure, their appropriate Operation will be called when the structure's Operation is called.
This means that the client does not need any special knowledge or interface with the structure in order to use the embellishments. This is a Decorator pattern, one that adds responsibilities to an object without modifying the object itself. Look-and-feel refers to platform-specific UI standards. These standards 'define guidelines for how applications appear and react to the user' pp. Since object creation of different concrete objects cannot be done at runtime, the object creation process must be abstracted.
This is done with an abstract guiFactory, which takes on the responsibility of creating UI elements. The abstract guiFactory has concrete implementations, such as MotifFactory, which creates concrete elements of the appropriate type MotifScrollBar. In this way, the program need only ask for a ScrollBar and, at run-time, it will be given the correct concrete element.
This is an Abstract Factory. A regular factory creates concrete objects of one type. An abstract factory creates concrete objects of varying types, depending on the concrete implementation of the factory itself. Its ability to focus on not just concrete objects, but entire families of concrete objects 'distinguishes it from other creational patterns, which involve only one kind of product object' pp.
Just as look-and-feel is different across platforms, so is the method of handling windows. Each platform displays, lays out, handles input to and output from, and layers windows differently.
It is possible to develop 'our own abstract and concrete product classes', because 'all window systems do generally the same thing' p. An abstract base Window class can be derived to the different types of existing windows, such as application, iconified, dialog.
These classes will contain operations that are associated with windows, such as reshaping, graphically refreshing, etc. Each window contains elements, whose Draw functions are called upon by the Window 's own draw-related functions. In order to avoid having to create platform-specific Window subclasses for every possible platform, an interface will be used.
The Window class will implement a Window implementation WindowImp abstract class. This class will then in turn be derived into multiple platform-specific implementations, each with platform-specific operations. Hence, only one set of Window classes are needed for each type of Window , and only one set of WindowImp classes are needed for each platform rather than the Cartesian product of all available types and platforms.
In addition, adding a new window type does not require any modification of platform implementation, or vice versa.
This is a Bridge pattern. Window and WindowImp are different, but related. Window deals with windowing in the program, and WindowImp deals with windowing on a platform. One of them can change without ever having to modify the other. 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. The DataObject implementations can evolve dynamically without changing any clients.
The DataObject abstract class has been replaced by an interface because DataObject contains no implementation code. NetOptimized Bridge: when and where use it The Bridge pattern is used for decoupling an abstraction from its implementation so that the two can vary independently. Bridge is a high-level architectural patterns and its main goal is through abstraction to help. NET developers write better code. 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.
The abstraction decouples the client, the interface, and the implementation. A classic example of the Bridge pattern is when coding against device drivers. A driver is an object that independently operates a computer system or external hardware device.
It is important to realize that the client application is the abstraction. Interestingly enough, each driver instance is an implementation of the Adapter pattern. The overall system, the application together with the drivers, represents an instance of a Bridge. Bridge in the. NET Framework Bridge is a high-level architectural pattern and as such is not exposed by the.
NET libraries themselves. Most developers are not aware of this, but they use this pattern all the time. The ODBC architecture decouples an abstraction from its implementation so that the two can vary independently — the Bridge pattern in action. Composite Definition Compose objects into tree structures to represent part-whole hierarchies.
Composite lets clients treat individual objects and compositions of objects uniformly. A leaf has no children. Composite CompositeElement o defines behavior for components having children. Client CompositeApp o manipulates objects in the composition through the Component interface. 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, circles, etc and composite nodes groups of drawing elements that make up more complex elements. The composite pattern is a great candidate for generics and you will find these used throughout this example. This is an open type which has the ability to accept any type parameter.
The class named Shape does implement this generic interface so that comparisons can be made between shape objects. This facilitates the process of adding and removing shapes from the list of tree nodes. This code demonstrates much of the power that generics offer to. NET developers. Numerous interesting language features are used in this example, including generics, automatic properties, and recursion the Display method.
NetOptimized Composite: when and where use it The Composite design pattern is an in-memory data structures with groups of objects, each of which contain individual items or other groups. A tree control is a good example of a Composite pattern. The nodes of the tree either contain an individual object leaf node or a group of objects a subtree of nodes.
All nodes in the Composite pattern share a common interface which supports individual items as well as groups of items. This common interface greatly facilitates the design and construction of recursive algorithms that iterate over each object in the Composite collection. Fundamentally, the Composite pattern is a collection that you use to build trees and directed graphs.
It is used like any other collection, such as, arrays, list, stacks, dictionaries, etc. Composite in the. Examples are the two Control classes one for Windows apps in the System. Forms namespace and the other for ASP. NET apps in the System. UI namespace. The built-in. NET framework. WPF also has many built-in controls that are Composites.
Decorator Definition Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality. Decorator Decorator o maintains a reference to a Component object and defines an interface that conforms to Component's interface. Structural sample code The structural code demonstrates the Decorator pattern which dynamically adds extra functionality to an existing object.
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.
NET optimized code demonstrates an example of the Decorator design pattern that uses generics; the collection of borrowers is represents in a type-safe collection of type List List Of String in VB. A NET 3. It is polymorphic with the original class so that clients can invoke it just like the original class. In most cases, method calls are delegated to the original class and then the results are acted upon, or decorated, with additional functionality. Decoration is a flexible technique because it takes place at runtime, as opposed to inheritance which take place at compile time.
Decorator in the. NET Framework include a set of classes that are designed around the Stream class. The Stream class is an abstract class that reads or writes a sequence of bytes from an IO device disk, sockets, memory, etc. The BufferedStream class is a Decorator that wraps the Stream class and reads and writes large chunks of bytes for better performance.
Similarly, the CryptoStream class wraps a Stream and encrypts and decrypts a stream of bytes on the fly. Decorator classes usually have a constructor with an argument that represents the class they intent to decorate: for example: new BufferedStream Stream stream. As an aside, the new. Similarly, attached properties and attached events which are used in WPF, also allow extending classes dynamically without changing the classes themselves.
Facade Definition Provide a unified interface to a set of interfaces in a subsystem. Subsystem classes Bank, Credit, Loan o implement subsystem functionality. Structural sample code The structural code demonstrates the Facade pattern which provides a simplified and uniform interface to a large subsystem of classes. 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. The only difference is the use of. In fact, its use will only increase with the shift towards Web Services and Service Oriented Architectures.
In a 3-tier application the presentation layer is the client. Calls into the business layer take place via a well defined service layer. Facades themselves are often implemented as singleton abstract factories. Facade in the. NET Framework In the. It is used in scenarios where there is a need to present a simplified view over more complex set of types. To discuss this properly we need to distinguish high-level architectural Facades from lower level component type facades.
An example of an aggregate component is System. Complex operations, including opening and closing read-and-write handles are totally hidden from the client. SmtpMail to send mail messages, System. SerialPort which is a powerful serial port class, System. MessageQueue which provides access to a queue on a Message Queue server, and System. WebClient which provides a high-level interface for sending and retrieving data from a network resources identified by a general URI. NET Framework libraries are no exception.
The objective of the. NET developer can see. Flyweigth Definition Use sharing to support large numbers of fine-grained objects efficiently. A ConcreteFlyweight object must be sharable. Any state it stores must be intrinsic, that is, it must be independent of the ConcreteFlyweight object's context. The Flyweight interface enables sharing, but it doesn't enforce it.
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. When a client requests a flyweight, the FlyweightFactory objects supplies an existing instance or creates one, if none exists. 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.
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. However, it is valuable as a memory management technique when many objects are created with similar state. NET uses Flyweights for strings that are declared at compile time and have the same sequence of characters.
The stateless flyweights refer to the same memory location that holds the immutable string. Flyweights are usually combined with the Factory pattern as demonstrated in the. NET Optimized code sample. NET optimized code uses a generic Dictionary collection to hold and quickly access Flyweight Character objects in memory. The generic collection increases the type-safety of the code. NetOptimized Flyweight: when and where use it The intent of the Flyweight design pattern is to share large numbers of fine-grained objects efficiently.
Shared flyweight objects are immutable, that is, they cannot be changed as they represent the characteristics that are shared with other objects.
Examples include, characters and line-styles in a word processor or digit receivers in a public switched telephone network application. You will find flyweights mostly in utility type applications word processors, graphics programs, network apps. They are rarely used in data-driven business type applications. Flyweight in the. NET Framework as a string management technique to minimize memory usage for immutable strings. Proxy Definition Provide a surrogate or placeholder for another object to control access to it.
Proxy may refer to a Subject if the RealSubject and Subject interfaces are the same. For example, the ImageProxy from the Motivation caches the real images's extent.
Structural sample code The structural code demonstrates the Proxy pattern which provides a representative object proxy that controls access to another similar object. Structural Real-world sample code The real-world code demonstrates the Proxy pattern for a Math object represented by a MathProxy object.
This code demonstrates the Remote Proxy pattern which provides a representative object i. In fact, the 'math' member variable in the MathProxy object is the 'hidden'. NetOptimized Proxy: when and where use it In object-oriented languages objects do the work they advertise through their public interface. Clients of these objects expect this work to be done quickly and efficiently. However, there are situations where an object is severely constrained and cannot live up to its responsibility.
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 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.
The proxy pattern is meant to provide a surrogate or placeholder for another object to control access to it. Actually, there is another type, called Smart References. A Smart Reference is a proxy for a pointer, but since there are few uses for pointers in. NET Framework In. NET the Proxy pattern manifests itself in the Remoting infrastructure. NET Remoting, whenever an object requires access to an object in a different address space app domain, process, or machine a proxy is created that sends the request to the remote object and any data it needs.
As is common with proxies, the client is frequently not even aware that a proxy is at work. Clients of WCF services also rely heavily on auto-generated proxy objects. 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. Chain the receiving objects and pass the request along the chain until an object handles it. 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.
Each position has can have its own set of rules which orders they can approve. The Successor settings are simplified by using properties.
Furthermore, this example uses an event driven model with events, delegates, and custom event arguments. 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, for example, the first argument in the DirectorRequest event handler.
The Purchase and other classes use. 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. NetOptimized Chain of Responsibility: when and where use it An important goal of object-oriented design is to keep objects loosely coupled by limiting their dependencies and keeping the relationships between objects specific and minimal.
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. 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. This search is usually modeled according to the specific needs of the application domain. Note that Chain-of-Responsibility is not commonly used in business application development. Chain of Responsibility in the.
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.
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, in which each object does some processing on the message as it travels through the chain from the sender to the receiver. This is slightly different from the GoF definition in which just one object in a chain decides to handle the request.
NET Remoting in which a message between a client and a server passes through one or more so-called message sinks. Message sinks form a chain as each sink has a reference to the next sink in the chain.
Command Definition Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations. Structural sample code The structural code demonstrates the Command pattern which stores requests as objects allowing clients to execute or playback the requests. 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.
Note that in C the word 'operator' is a keyword. 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.
The classic usage of this pattern is a menu system where each command object represents an action and an associated undo action. Menu actions include menu items such as File Open, File Save, Edit Copy, etc each of which gets mapped to its own command object. All Commands implement the same interface, so they can be handled polymorphically.
Typically their interface includes methods such as Do and Undo or Execute and Undo. Areas where you find Command patterns are: menu command systems and in applications that require undo functionality word processors, and sometimes in business applications that need database undo functionality. Command in the. NET, use the Command pattern to support their menus, toolbars, shortcuts, and associated undo functionality.
We would have expected that the Command pattern would be exposed in. NET as part of a unified WinForms command routing architecture, but they are not.
So, until recently the Command patterns was not generally used in the. Interpreter Definition Given a language, define a representation for its grammar along with an interpreter that uses the representation to interpret sentences in the language.. Rn in the grammar o maintains instance variables of type AbstractExpression for each of the symbols R1 through Rn. Interpret typically calls itself recursively on the variables representing R1 through Rn. 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, which using a defined grammer, provides the interpreter that processes parsed statements Code in project: DoFactory.
Structural Real-world sample code The real-world code demonstrates the Interpreter pattern which is used to convert a Roman numeral to a decimal. Here the abstract classes have been replaced by interfaces because the abstract classes have no implementation code. In addition, the parse tree which holds the collection of expressions ThousandExpression, HundredExpression, etc is implemented as a generic List of type Expression.
NetOptimized Interpreter: when and where use it If your applications are complex and require advanced configuration you could offer a scripting language which allows the end-user to manipulate your application through simple scripting.
The Interpreter design pattern solves this particular problem — that of creating a scripting language that allows the end user to customize their solution. 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. NET Dynamic Languages. Certain types of problems lend themselves to be characterized by a language. This language describes the problem domain which should be well-understood and welldefined.
In addition, this language needs to be mapped to a grammar. Grammars are usually hierarchical tree-like structures that step through multiple levels but end up with terminal nodes also called literals. This type of problem, expressed as a grammar, can be implemented using the Interpreter design pattern. 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.
Just like State and Strategy, it delegates processing to a set of dedicated classes. It also has similarities with the Composite pattern; basically Interpreter is an enhancement of Composite although it frequently requires more complex object groupings compared to the Composite pattern.
Interpreter in the. NET Framework libraries. Thanks John, really appreciate your effort a lot! Finding a design pattern blog post that stitches together ideas has been challenging.
There is also a great website called refactoring. UML is too much of an abstraction. Beginners to intermediate programmers need real-world example to really grasp the core ideas. But if said book were to be published l would be near the top of a very long list to acquire an initial beta release.
I just wanted to throw that out there to get your thoughts. In template method pattern, most of the examples show template method as final.
Is it not necessary? Hi there. My Firefox Developer Edition browser shows this page with no border nor padding. Your email address will not be published. Save my name, email, and website in this browser for the next time I comment.