tag:blogger.com,1999:blog-49379263076170664402012-02-16T20:42:19.927-08:00All patterns here.Al. Shv.http://www.blogger.com/profile/12088581895105074887noreply@blogger.comBlogger191100tag:blogger.com,1999:blog-4937926307617066440.post-43846297659798544412007-02-18T05:59:00.000-08:002008-01-19T00:06:09.874-08:00

Intent Define an object that encapsulates how a set of objects interact. Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and it lets you vary their interaction independently. Design an intermediary to decouple many peers. Promote the many-to-many relationships between interacting peers to "full object status". Problem We want to design reusable

Al. Shv.http://www.blogger.com/profile/12088581895105074887noreply@blogger.com0tag:blogger.com,1999:blog-4937926307617066440.post-20714985546974406862007-02-18T05:56:00.000-08:002008-01-19T00:06:52.322-08:00

Intent Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation. The C++ and Java standard library abstraction that makes it possible to decouple collection classes and algorithms. Promote to "full object status" the traversal of a collection. Polymorphic traversal Problem Need to "abstract" the traversal of wildly different

Al. Shv.http://www.blogger.com/profile/12088581895105074887noreply@blogger.com0tag:blogger.com,1999:blog-4937926307617066440.post-76809159806399587052007-02-16T03:32:00.000-08:002008-01-19T00:07:15.699-08:00

Intent Given a language, define a representation for its grammar along with an interpreter that uses the representation to interpret sentences in the language. Map a domain to a language, the language to a grammar, and the grammar to a hierarchical object-oriented design. Problem A class of problems occurs repeatedly in a well-defined and well-understood domain. If the domain were

Al. Shv.http://www.blogger.com/profile/12088581895105074887noreply@blogger.com0tag:blogger.com,1999:blog-4937926307617066440.post-28329870942077047742007-02-16T03:09:00.000-08:002008-01-19T00:10:39.410-08:00

Intent Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations. Promote "invocation of a method on an object" to full object status An object-oriented callback Problem Need to issue requests to objects without knowing anything about the operation being requested or the receiver of the

Al. Shv.http://www.blogger.com/profile/12088581895105074887noreply@blogger.com0tag:blogger.com,1999:blog-4937926307617066440.post-62760782876086736272007-02-16T02:41:00.000-08:002008-01-19T00:11:01.225-08:00

Intent 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. Launch-and-leave requests with a single processing pipeline that contains many possible handlers. An object-oriented linked list with recursive traversal. Problem There is a

Al. Shv.http://www.blogger.com/profile/12088581895105074887noreply@blogger.com0tag:blogger.com,1999:blog-4937926307617066440.post-27151919542464117832007-01-23T10:48:00.000-08:002008-01-19T00:11:26.928-08:00

Intent Provide a surrogate or placeholder for another object to control access to it. Use an extra level of indirection to support distributed, controlled, or intelligent access. Add a wrapper and delegation to protect the real component from undue complexity. Problem You need to support resource-hungry objects, and you do not want to instantiate such objects unless and until they are

Al. Shv.http://www.blogger.com/profile/12088581895105074887noreply@blogger.com0tag:blogger.com,1999:blog-4937926307617066440.post-15587366897969349312007-01-23T10:46:00.000-08:002007-01-23T11:00:10.501-08:00

Sorry for little delay in my posting, guys. Here, in Ukraine we are not stopping to celebrate New Year until 20th of January :) Yeah, vodka, bears and so on.

Al. Shv.http://www.blogger.com/profile/12088581895105074887noreply@blogger.com0tag:blogger.com,1999:blog-4937926307617066440.post-3105447099226514442007-01-23T10:24:00.000-08:002008-01-19T00:11:48.446-08:00

Intent Use sharing to support large numbers of fine-grained objects efficiently. The Motif GUI strategy of replacing heavy-weight widgets with light-weight gadgets. Problem Designing objects down to the lowest levels of system "granularity" provides optimal flexibility, but can be unacceptably expensive in terms of performance and memory usage. Discussion The Flyweight pattern describes

Al. Shv.http://www.blogger.com/profile/12088581895105074887noreply@blogger.com0tag:blogger.com,1999:blog-4937926307617066440.post-59305307510456686372007-01-05T09:30:00.000-08:002008-01-19T00:12:12.507-08:00

Intent Provide a unified interface to a set of interfaces in a subsystem. Facade defines a higher-level interface that makes the subsystem easier to use. Wrap a complicated subsystem with a simpler interface. Problem A segment of the client community needs a simplified interface to the overall functionality of a complex subsystem. Discussion Facade discusses encapsulating a complex

Al. Shv.http://www.blogger.com/profile/12088581895105074887noreply@blogger.com0tag:blogger.com,1999:blog-4937926307617066440.post-58337486238551627652006-12-25T15:10:00.000-08:002008-01-19T00:12:34.811-08:00

Intent Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality. Client-specified embellishment of a core object by recursively wrapping it. Wrapping a gift, putting it in a box, and wrapping the box. Problem You want to add behavior or state to individual objects at run-time. Inheritance is not

Al. Shv.http://www.blogger.com/profile/12088581895105074887noreply@blogger.com0tag:blogger.com,1999:blog-4937926307617066440.post-25454939598584986942006-12-23T12:51:00.000-08:002008-01-19T00:12:57.960-08:00

Intent Compose objects into tree structures to represent whole-part hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly. Recursive composition "Directories contain entries, each of which could be a directory." 1-to-many "has a" up the "is a" hierarchy Problem Application needs to manipulate a hierarchical collection of "primitive" and "

Al. Shv.http://www.blogger.com/profile/12088581895105074887noreply@blogger.com0tag:blogger.com,1999:blog-4937926307617066440.post-81880445443334029302006-12-20T13:50:00.000-08:002008-01-19T00:13:27.139-08:00

Intent Decouple an abstraction from it's implementation so that the two can vary independently. Publish interface in an inheritance hierarchy, and bury implementation in its own inheritance hierarchy. Beyond encapsulation, to insulation Problem "Hardening of the software arteries" has occurred by using subclassing of an abstract base class to provide alternative implementations. This locks

Al. Shv.http://www.blogger.com/profile/12088581895105074887noreply@blogger.com5tag:blogger.com,1999:blog-4937926307617066440.post-73479222661760451272006-12-14T16:00:00.000-08:002008-01-19T00:13:54.894-08:00

Intent Convert the interface of a class into another interface clients expect. Adapter lets classes work together that couldn't otherwise because of incompatible interfaces. Wrap an existing class with a new interface. Impedance match an old component to a new system Problem An "off the shelf" component offers compelling functionality that you would like to reuse, but its "view of the

Al. Shv.http://www.blogger.com/profile/12088581895105074887noreply@blogger.com0tag:blogger.com,1999:blog-4937926307617066440.post-47401783877264451312006-12-03T13:55:00.000-08:002006-12-05T12:21:00.306-08:00

C++ Report "Pattern Hatching" column for June '96 issue John Vlissides The Singleton pattern is remarkably simple. Its intent states, Ensure a class only has one instance, and provide a global point of access to it. It's also flexible, as we saw last time when we applied it to our file system design. It helped us encapsulate the creation of User objects, which give file system users the

Al. Shv.http://www.blogger.com/profile/12088581895105074887noreply@blogger.com0tag:blogger.com,1999:blog-4937926307617066440.post-17162054859749428492006-12-03T13:49:00.000-08:002008-01-19T00:14:23.438-08:00

Intent Ensure a class has only one instance, and provide a global point of access to it. Encapsulated "just-in-time initialization" or "initialization on first use". Problem Application needs one, and only one, instance of an object. Additionally, lazy initialization and global access are necessary. Discussion Make the class of the single instance object responsible for creation,

Al. Shv.http://www.blogger.com/profile/12088581895105074887noreply@blogger.com3tag:blogger.com,1999:blog-4937926307617066440.post-86390938315130905462006-12-02T13:24:00.000-08:002008-01-19T00:14:50.627-08:00

Intent Specify the kinds of objects to create using a prototypical instance, and create new objects by copying this prototype. Co-opt one instance of a class for use as a breeder of all future instances. The new operator considered harmful. Problem Application "hard wires" the class of object to create in each "new" expression. Discussion Declare an abstract base class that specifies a

Al. Shv.http://www.blogger.com/profile/12088581895105074887noreply@blogger.com0tag:blogger.com,1999:blog-4937926307617066440.post-3373219464185383562006-11-30T15:28:00.000-08:002008-01-19T00:15:21.772-08:00

Intent Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses. Defining a "virtual" constructor. The new operator considered harmful. Problem A framework needs to standardize the architectural model for a range of applications, but allow for individual applications to define their own

Al. Shv.http://www.blogger.com/profile/12088581895105074887noreply@blogger.com0tag:blogger.com,1999:blog-4937926307617066440.post-78028534045570645172006-11-30T15:25:00.001-08:002008-01-19T00:15:45.197-08:00

Intent Separate the construction of a complex object from its representation so that the same construction process can create different representations. Parse a complex representation, create one of several targets. Problem An application needs to create the elements of a complex aggregate. The specification for the aggregate exists on secondary storage and one of many representations needs

Al. Shv.http://www.blogger.com/profile/12088581895105074887noreply@blogger.com0tag:blogger.com,1999:blog-4937926307617066440.post-21738794290999724072006-11-30T14:42:00.000-08:002008-01-19T00:16:14.386-08:00

Intent Provide an interface for creating families of related or dependent objects without specifying their concrete classes. A hierarchy that encapsulates: many possible "platforms", and the construction of a suite of "products". The new operator considered harmful. Problem If an application is to be portable, it needs to encapsulate platform dependencies. These "platforms" might include:

Al. Shv.http://www.blogger.com/profile/12088581895105074887noreply@blogger.com0