In software engineering, a design pattern is a general reusable solution to a commonly occurring problem in software design. Software engineering is the application of a systematic disciplined quantifiable approach to the development operation and maintenance of Software. Software design is a process of problem-solving and planning for a Software solution A design pattern is not a finished design that can be transformed directly into code. In Computer science, source code (commonly just source or code) is any sequence of statements or declarations written in some Human-readable It is a description or template for how to solve a problem that can be used in many different situations. Object-oriented design patterns typically show relationships and interactions between classes or objects, without specifying the final application classes or objects that are involved. Object-oriented programming (OOP is a Programming paradigm that uses " objects " and their interactions to design applications and computer programs Interaction is a kind of action that occurs as two or more objects have an Effect upon one another In Object-oriented programming, a class is a Programming language construct that is used as a blueprint to create objects This blueprint includes attributes In its simplest embodiment an object is an allocated region of storage Algorithms are not thought of as design patterns, since they solve computational problems rather than design problems. In Mathematics, Computing, Linguistics and related subjects an algorithm is a sequence of finite instructions often used for Calculation Computation is a general term for any type of Information processing. Design is used both as a Noun and a Verb. The term is often tied to the various Applied arts and Engineering (See design disciplines
Not all software patterns are design patterns. Design patterns deal specifically with problems at the level of software design. Other kinds of patterns, such as architectural patterns, describe problems and solutions that have alternative scopes. Architectural patterns are software patterns that offer well-established solutions to architectural problems in Software engineering.
Patterns originated as an architectural concept by Christopher Alexander (1977/79). Pattern in architecture is the idea of capturing architectural design ideas as archetypal and reusable descriptions Christopher Alexander (born October 4, 1936 in Vienna, Austria) is an architect noted for his theories about design and for more than 200 In 1987, Kent Beck and Ward Cunningham began experimenting with the idea of applying patterns to programming and presented their results at the OOPSLA conference that year. Kent Beck is the creator of Extreme Programming Beck has pioneered software design patterns, the rediscovery of Test-driven development, as well as OOPSLA ( Object-Oriented Programming, Systems Languages & Applications is an annual ACM conference  In the following years, Beck, Cunningham and others followed up on this work.
Design patterns gained popularity in computer science after the book Design Patterns: Elements of Reusable Object-Oriented Software was published in 1994 (Gamma et al. Computer science (or computing science) is the study and the Science of the theoretical foundations of Information and Computation and their Design Patterns Elements of Reusable Object-Oriented Software (ISBN 0-201-63361-2 is a Software engineering book describing recurring Year 1994 ( MCMXCIV) was a Common year starting on Saturday (link will display full 1994 Gregorian calendar) ). That same year, the first Pattern Languages of Programming Conference was held and the following year, the Portland Pattern Repository was set up for documentation of design patterns. Pattern Languages of Programming is the name of a group of annual conferences The Portland Pattern Repository ( PPR) is a repository for computer programming design patterns It was accompanied by a companion website WikiWikiWeb, which The scope of the term remains a matter of dispute. Notable books in the design pattern genre include:
Although the practical application of design patterns is a phenomenon, formalization of the concept of a design pattern languished for several years. 
Design patterns can speed up the development process by providing tested, proven development paradigms. Effective software design requires considering issues that may not become visible until later in the implementation. Reusing design patterns helps to prevent subtle issues that can cause major problems, and it also improves code readability for coders and architects who are familiar with the patterns.
In order to achieve flexibility, design patterns usually introduce additional levels of indirection, which in some cases may complicate the resulting designs and hurt application performance.
By definition, a pattern must be programmed anew into each application that uses it. Since some authors see this as a step backward from software reuse as provided by components, researchers have worked to turn patterns into components. Code reuse, also called software reuse is the use of existing software or software knowledge to build new software Component-based software engineering (CBSE (also known as Component-Based Development (CBD or Software Componentry) is a branch of the Software engineering Meyer and Arnout claim a two-thirds success rate in componentizing the best-known patterns. 
Often, people only understand how to apply certain software design techniques to certain problems. These techniques are difficult to apply to a broader range of problems. Design patterns provide general solutions, documented in a format that doesn't require specifics tied to a particular problem. Documentation may refer to the process of providing evidence ("to document something" or to the communicable material used to provide such documentation (i
Design patterns are composed of several sections (see Documentation below). In Software engineering, a design pattern is a general reusable solution to a commonly occurring problem in Software design. Of particular interest are the Structure, Participants, and Collaboration sections. These sections describe a design motif: a prototypical micro-architecture that developers copy and adapt to their particular designs to solve the recurrent problem described by the design pattern. A micro-architecture is a set of program constituents (e. g. , classes, methods. . . ) and their relationships. Developers use the design pattern by introducing in their designs this prototypical micro-architecture, which means that micro-architectures in their designs will have structure and organization similar to the chosen design motif.
In addition, patterns allow developers to communicate using well-known, well understood names for software interactions. Common design patterns can be improved over time, making them more robust than ad-hoc designs.
Efforts have also been made to codify design patterns in particular domains, including use of existing design patterns as well as domain specific design patterns. Examples include User Interface design patterns, Information Visualization  and web design. Information graphics or infographics are visual representations of Information, Data or Knowledge. 
The Pattern Languages of Programming Conference(annual,1994->) proceedings includes many examples of domain specific patterns. Pattern Languages of Programming is the name of a group of annual conferences
Design Patterns originally grouped design patterns into the categories Creational Patterns, Structural Patterns, and Behavioral Patterns, and described them using the concepts of delegation, aggregation, and consultation. Design Patterns Elements of Reusable Object-Oriented Software (ISBN 0-201-63361-2 is a Software engineering book describing recurring In Software engineering, creational design patterns are design patterns that deal with object creation mechanisms trying to create objects in a manner In Software Engineering, Structural Design Patterns are Design Patterns that ease the design by identifying a simple way to realize relationships between entities In Software engineering, behavioral design patterns are design patterns that identify common communication patterns between objects and realize these patterns In Object-oriented programming there are two related notions of delegation. In Computer science, object composition (not to be confused with function composition) is a way and practice to combine simple objects or Consultation in Object-oriented programming occurs when an object's method implementation consists of a message send of the same message to another constituent object For further background on object-oriented design, see coupling and cohesion. In Computer science, coupling or dependency is the degree to which each program module relies on each one of the other modules In Computer programming, cohesion is a measure of how strongly-related and focused the various responsibilities of a software module are For further background on object-oriented programming, see inheritance, interface, and polymorphism. In Object-oriented programming, inheritance is a way to form new classes (instances of which are called objects using classes that have already been defined Interface generally refers to an abstraction that an entity provides of itself to the outside In simple terms polymorphism is the ability of one type A to appear as and be used like another type B Another classification has also introducted the notion of architectural design pattern which may be applied at the architecture level of the software such as the Model-View-Controller pattern. Architectural patterns are software patterns that offer well-established solutions to architectural problems in Software engineering. Model-view-controller ( MVC) is an architectural pattern used in Software engineering.
|Name||Description||In Design Patterns||In Code Complete|
|Abstract factory||Provide an interface for creating families of related or dependent objects without specifying their concrete classes. Design Patterns Elements of Reusable Object-Oriented Software (ISBN 0-201-63361-2 is a Software engineering book describing recurring Code Complete is a Software development book written by Steve McConnell and published by Microsoft Press, urging developers to get past In Software engineering, creational design patterns are design patterns that deal with object creation mechanisms trying to create objects in a manner A software design pattern, the Abstract Factory Pattern provides a way to encapsulate a group of individual factories that have a common theme||Yes||Yes|
|Factory method||Define an interface for creating an object, but let subclasses decide which class to instantiate. The factory method pattern is an Object-oriented design pattern. Factory Method lets a class defer instantiation to subclasses.||Yes||Yes|
|Builder||Separate the construction of a complex object from its representation so that the same construction process can create different representations. The Builder Pattern is a software design pattern. The intention is to separate the construction of a complex object from its representation so that the same construction process||Yes||No|
|Lazy initialization||Tactic of delaying the creation of an object, the calculation of a value, or some other expensive process until the first time it is needed. In Computer programming, lazy initialization is the tactic of delaying the creation of an object the calculation of a value or some other expensive process until the first||No||No|
|Object pool||Avoid expensive acquisition and release of resources by recycling objects that are no longer in use||No||No|
|Prototype||Specify the kinds of objects to create using a prototypical instance, and create new objects by copying this prototype. In Computer programming, an object pool is a software design pattern. A prototype pattern is a creational design pattern used in software development when the type of objects to create is determined by a prototypical instance which is cloned to||Yes||No|
|Singleton||Ensure a class only has one instance, and provide a global point of access to it. In Software engineering, the singleton pattern is a design pattern that is used to restrict instantiation of a class to one object.||Yes||Yes|
|Utility||A class with a private constructor that contains only static methods.|
|Adapter||Convert the interface of a class into another interface clients expect. In Software Engineering, Structural Design Patterns are Design Patterns that ease the design by identifying a simple way to realize relationships between entities In Computer programming, the adapter design pattern (often referred to as the wrapper pattern or simply a wrapper) translates one interface Adapter lets classes work together that couldn't otherwise because of incompatible interfaces.||Yes||Yes|
|Bridge||Decouple an abstraction from its implementation so that the two can vary independently. The bridge pattern is a design pattern used in Software engineering which is meant to "decouple an abstraction from its Implementation||Yes||Yes|
|Composite||Compose objects into tree structures to represent part-whole hierarchies. In Computer science, the composite pattern is a partitioning design pattern. Composite lets clients treat individual objects and compositions of objects uniformly.||Yes||Yes|
|Decorator||Attach additional responsibilities to an object dynamically. In Object-oriented programming, the decorator pattern is a design pattern that allows new/additional behaviour to be added to an existing class dynamically Decorators provide a flexible alternative to subclassing for extending functionality.||Yes||Yes|
|Facade||Provide a unified interface to a set of interfaces in a subsystem. The facade pattern or façade pattern is a Software engineering design pattern commonly used with Object-oriented programming. Facade defines a higher-level interface that makes the subsystem easier to use.||Yes||Yes|
|Flyweight||Use sharing to support large numbers of fine-grained objects efficiently. Flyweight is a software design pattern. A Flyweight is an object that minimizes memory occupation by sharing as much data as possible with other similar objects it is a way||Yes||No|
|Proxy||Provide a surrogate or placeholder for another object to control access to it. In Computer programming, the proxy pattern is a Software design pattern.||Yes||No|
|Chain of responsibility||Avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request. In Software engineering, behavioral design patterns are design patterns that identify common communication patterns between objects and realize these patterns In Object Oriented Design, the chain-of-responsibility pattern is a design pattern consisting of a source of command objects and a series of processing Chain the receiving objects and pass the request along the chain until an object handles it.||Yes||No|
|Command||Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations. In Object-oriented programming, the Command pattern is a design pattern in which objects are used to represent actions Undo is a command in many computer programs It erases the last change done to the document reverting it to an older state||Yes||No|
|Interpreter||Given a language, define a representation for its grammar along with an interpreter that uses the representation to interpret sentences in the language. In Computer programming, the interpreter pattern is a particular design pattern.||Yes||No|
|Iterator||Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation. In Object-oriented programming, the Iterator pattern is a design pattern in which iterators are used to access the elements of an aggregate object||Yes||Yes|
|Mediator||Define an object that encapsulates how a set of objects interact. The mediator pattern is a Software design pattern that provides an unified interface to a set of interfaces in a Subsystem. Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and it lets you vary their interaction independently.||Yes||No|
|Memento||Without violating encapsulation, capture and externalize an object's internal state so that the object can be restored to this state later. The memento pattern is a software design pattern that provides the ability to restore an object to its previous state ( Undo via rollback||Yes||No|
|Observer||Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically. The observer pattern (sometimes known as Publish/subscribe) is a design pattern used in computer programming to observe the state of an object in a||Yes||Yes|
|State||Allow an object to alter its behavior when its internal state changes. The state pattern is a behavioral Software design pattern, also known as the objects for states pattern. The object will appear to change its class.||Yes||No|
|Strategy||Define a family of algorithms, encapsulate each one, and make them interchangeable. In Computer programming, the strategy pattern (also known as the policy pattern) is a particular software design pattern, whereby Algorithms can Strategy lets the algorithm vary independently from clients that use it.||Yes||Yes|
|Specification||Recombinable Business logic in a boolean fashion||No||No|
|Template method||Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. In computer programming the specification pattern is a particular Software design pattern, whereby business logic can be recombined by chaining the business logic together using boolean In Software engineering, the template method pattern is a design pattern. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure.||Yes||Yes|
|Visitor||Represent an operation to be performed on the elements of an object structure. In Object-oriented programming and Software engineering, the visitor design pattern is a way of separating an Algorithm from an object Visitor lets you define a new operation without changing the classes of the elements on which it operates.||Yes||No|
|Single-serving visitor||Optimize the implementation of a visitor that is allocated, used only once, and then deleted||No||No|
|Hierarchical visitor||Provide a way to visit every node in a hierarchical data structure such as a tree. In Computer programming, the single-serving visitor pattern is a design pattern. In Software engineering, the hierarchical visitor pattern is one of design patterns that intend to provide a way to visit every node in the hierarchical Data A data structure in Computer science is a way of storing Data in a computer so that it can be used efficiently||No||No|
|Double checked locking||No||No|
|Read write lock||No||No|
The documentation for a design pattern describes the context in which the pattern is used, the forces within the context that the pattern seeks to resolve, and the suggested solution. In Software engineering, concurrency patterns are one of the types of design patterns. The Active Object Design pattern decouples method execution from method invocation that reside in their own thread of control The Balking pattern is a software design pattern that only executes an action on an object when the object is in a particular state In Software engineering, double-checked locking is a Software design pattern also known as "double-checked locking optimization" In concurrent programming, guarded suspension is a software design pattern for managing operations that require both a lock to be acquired and a Precondition A monitor is an approach to synchronize two or more computer tasks that use a shared resource usually a hardware device or a set of Variables With monitor-based A read/write lock pattern or simply RWL is a Software design pattern that allows concurrent read access to an object but requires exclusive access In Computer programming, the scheduler pattern is a Software design pattern. In the thread pool pattern in Programming, a number of threads are created to perform a number of tasks which are usually organized in a queue. Thread-local storage (TLS is a computer programming method that uses Static or Global memory local to a thread. The reactor Design pattern is a Concurrent programming pattern for handling service requests delivered concurrently to a service handler by one or more inputs  There is no single, standard format for documenting design patterns. Rather, a variety of different formats have been used by different pattern authors. However, according to Martin Fowler certain pattern forms have become more well-known than others, and consequently become common starting points for new pattern writing efforts. Martin Fowler is an author and international speaker on software architecture specializing in object-oriented analysis and design UML, patterns, and  One example of a commonly used documentation format is the one used by Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides (collectively known as the Gang of Four, or GoF for short) in their book Design Patterns. Erich Gamma (born 1961 in Zürich) is a co-author of the influential Computer science textbook Design Patterns. Richard Helm is currently with The Boston Consulting Group where he consults on the strategic application of technology to business For other people of the same name see Ralph Johnson (disambiguation Ralph E John Matthew Vlissides ( August 2 1961 - November 24 2005) was a software scientist known mainly as one of the four authors (referred to as the Design Patterns Elements of Reusable Object-Oriented Software (ISBN 0-201-63361-2 is a Software engineering book describing recurring Design Patterns Elements of Reusable Object-Oriented Software (ISBN 0-201-63361-2 is a Software engineering book describing recurring It contains the following sections:
In the field of computer science, there exist some criticisms regarding the concept of design patterns.
Peter Norvig, in Design Patterns in Dynamic Programming, discusses the triviality of implementing various patterns in dynamic languages. Peter Norvig is an American computer scientist. He is currently the Director of Research (formerly Director of Search Quality at Google Inc This article is about a class of programming languages for the method for reducing the runtime of algorithms see Dynamic programming.  Norvig and others have described language features that encapsulate or replace various patterns that a C++ user must implement for themselves.
Some authors allege that design patterns don't differ significantly from other forms of abstraction, and that the use of new terminology (borrowed from the architecture community) to describe existing phenomena in the field of programming is unnecessary. In Computer science, abstraction is a mechanism and practice to reduce and factor out details so that one can focus on a few concepts at a time The term architecture (from Greek αρχιτεκτονικήarchitektoniki) can be used to mean a process a profession or documentation The Model-View-Controller paradigm is touted as an example of a "pattern" which predates the concept of "design patterns" by several years. Model-view-controller ( MVC) is an architectural pattern used in Software engineering. It is further argued by some that the primary contribution of the Design Patterns community (and the Gang of Four book) was the use of Alexander's pattern language as a form of documentation; a practice which is often ignored in the literature.