A software design pattern describes a reusable solution to a commonly needed behavior in software.1 A design pattern is not a rigid structure to be copied directly into source code. Rather, it is a description of and a template for solving a particular type of problem that can be used in many different contexts, including different programming languages and computing platforms.2 Design patterns can be viewed as formalized best practices that the programmer may use to solve common problems when designing software.
Object-oriented design patterns typically show relationships and interactions between classes or objects, without specifying the final application classes or objects that are involved. Patterns that imply mutable state may be unsuited for functional programming languages. Some patterns can be rendered unnecessary in languages that have built-in support for solving the problem they are trying to solve, and object-oriented patterns are not necessarily suitable for non-object-oriented languages.3
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A pattern describes a design motif, also known as a prototypical micro-architecture, as a set of program constituents (e.g., classes, methods...) and their relationships.
Patterns originated as an architectural concept by Christopher Alexander as early as 1977 in A Pattern Language (cf. his article, "The Pattern of Streets," JOURNAL OF THE AIP, September, 1966, Vol. 32, No. 5, pp. 273–278). In 1987, Kent Beck and Ward Cunningham began experimenting with the idea of applying patterns to programming – specifically pattern languages – and presented their results at the OOPSLA conference that year.45 In the following years, Beck, Cunningham and others followed up on this work.
Although design patterns have been applied practically for a long time, formalization of the concept of design patterns languished for several years.7
Practice
Design patterns can speed up the development process by providing proven development paradigms.8 Effective software design requires considering issues that may not become apparent until later in the implementation. Freshly written code can often have hidden, subtle issues that take time to be detected – issues that sometimes can cause major problems down the road. Reusing design patterns can help to prevent such issues,9 and enhance code readability for those familiar with the patterns.
Software design techniques are difficult to apply to a broader range of problems. Design patterns provide general solutions, documented in a format that does not require specifics tied to a particular problem.10
In 1996, Christopher Alexander was invited to give a Keynote Speech to the 1996 OOPSLA Convention. Here he reflected on how his work on Patterns in Architecture had developed and his hopes for how the Software Design community could help Architecture extend Patterns to create living structures that use generative schemes that are more like computer code.
Motif
A pattern describes a design motif, also known as a prototypical micro-architecture, as a set of program constituents (e.g., classes, methods...) and their relationships. A developer adapts the motif to their codebase to solve the problem described by the pattern. The resulting code has structure and organization similar to the chosen motif.
Domain-specific patterns
Efforts have also been made to codify design patterns in particular domains, including the use of existing design patterns as well as domain-specific design patterns. Examples include user interface design patterns,11information visualization,12 secure design,13 "secure usability",14web design15 and business model design.16
Object-oriented design patterns typically show relationships and interactions between classes or objects, without specifying the final application classes or objects that are involved. Patterns that imply mutable state may be unsuited for functional programming languages. Some patterns can be rendered unnecessary in languages that have built-in support for solving the problem they are trying to solve, and object-oriented patterns are not necessarily suitable for non-object-oriented languages.
Examples
Design patterns can be organized into groups based on what kind of problem they solve.
Define an interface for creating a single object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses.
Yes
Yes
—N/a
Documentation
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.31 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.32 One example of a commonly used documentation format is the one used by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides in their book Design Patterns. It contains the following sections:
Name
A descriptive and unique name that helps in identifying and referring to the pattern.
Intent
A description of the goal behind the pattern and the reason for using it.
Also Known As
Other names for the pattern.
Motivation
A scenario consisting of a problem and a context in which this pattern can be used.
Applicability
Situations in which this pattern is usable; the context for the pattern.
Some suggest that the need for a design pattern may be a sign that a feature is missing from a programming language. Peter Norvig demonstrates that 16 out of the 23 patterns in the Design Patterns book (which is primarily focused on C++) are simplified or eliminated (via direct language support) in Lisp or Dylan.33 Related observations were made by Hannemann & Kiczales (2002) who implemented several of the 23 design patterns using an aspect-oriented programming language (AspectJ) and showed that code-level dependencies were removed from the implementations of 17 of the 23 design patterns and that aspect-oriented programming could simplify the implementations of design patterns.34 See also Paul Graham's essay "Revenge of the Nerds".35
Inappropriate use of patterns may unnecessarily increase complexity.36
By definition, a pattern must be programmed anew into each application that uses it.37 Since some authors see this as a step backward from software reuse as provided by components, researchers have worked to use generic programming facilities to turn patterns into components, in a process called componentization. were able to provide full or partial componentization of two-thirds of the patterns they attempted.
Related
The following concepts are similar in general nature yet differ from software design pattern:41421943
A reusable, proven solution to a recurring problem at the system level, addressing concerns related to the overall structure, component interactions, and quality attributes of the system.44 Software architecture patterns operate at a higher level of abstraction than design patterns, solving broader system-level challenges. While these patterns typically affect system-level concerns, the distinction between architectural patterns and architectural styles can sometimes be blurry. Examples include Circuit Breaker.414219
A high-level, structural organization that defines the overall system organization, specifying how components are organized, how they interact, and the constraints on those interactions. Architecture styles typically include a vocabulary of component and connector types, as well as semantic models for interpreting the system's properties. These styles represent the most coarse-grained level of system organization. Examples include Layered Architecture, , and .
4Smith, Reid (1987). "Panel on design methodology: OOPSLA '87 Panel Session". ACM SIGPLAN Notices. 23 (5). Association for Computing Machinery. doi:10.1145/62138.62151. “Ward cautioned against requiring too much programming at, what he termed, 'the high level of wizards.' He pointed out that a written 'pattern language' can significantly improve the selection and application of abstractions. He proposed a 'radical shift in the burden of design and implementation' basing the new methodology on an adaptation of Christopher Alexander's work in pattern languages and that programming-oriented pattern languages developed at has significantly aided their software development efforts.”
Beck, Kent (1997). Smalltalk Best Practice Patterns. Prentice–Hall. ISBN 978-0-13-476904-2.
Borchers, Jan (2001). A Pattern Approach to Interaction Design. John Wiley & Sons. ISBN 978-0-471-49828-5.
Brinch Hansen, Per (1995). Studies in Computational Science: Parallel Programming Paradigms. Prentice–Hall. ISBN 978-0-13-439324-7.
Buschmann, Frank; Meunier, Regine; Rohnert, Hans; Sommerlad, Peter (1996). Pattern-Oriented Software Architecture, Volume 1: A System of Patterns. John Wiley & Sons. ISBN 978-0-471-95869-7.
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. This pattern appears in the GoF catalog as "virtual proxy", an implementation strategy for the Proxy pattern.
Avoid expensive acquisition and release of resources by recycling objects that are no longer in use. Can be considered a generalisation of connection pool and thread pool patterns.
Specify the kinds of objects to create using a prototypical instance, and create new objects from the 'skeleton' of an existing object, thus boosting performance and keeping memory footprints to a minimum.
Convert the interface of a class into another interface clients expect. An adapter lets classes work together that could not otherwise because of incompatible interfaces. The enterprise integration pattern equivalent is the translator.
Compose objects into tree structures to represent part-whole hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly.
Attach additional responsibilities to an object dynamically keeping the same interface. Decorators provide a flexible alternative to subclassing for extending functionality.
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.
Encapsulate a request as an object, thereby allowing for the parameterization of clients with different requests, and the queuing or logging of requests. It also allows for the support of undoable operations.
Design an API to be method chained so that it reads like a DSL. Each method call returns a context through which the next logical method call(s) are made available.
Given a language, define a representation for its grammar along with an interpreter that uses the representation to interpret sentences in the language.
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 allows their interaction to vary independently.
Define a one-to-many dependency between objects where a state change in one object results in all its dependents being notified and updated automatically.
Define common functionality for a group of classes. The servant pattern is also frequently called helper class or utility class implementation for a given set of classes. The helper classes generally have no objects hence they have all static methods that act upon different kinds of class objects.
Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it.
Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. Template method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure.
Represent an operation to be performed on instances of a set of classes. Visitor lets a new operation be defined without changing the classes of the elements on which it operates.
Decouples method execution from method invocation that reside in their own thread of control. The goal is to introduce concurrency, by using asynchronous method invocation and a scheduler for handling requests.
The same calculation many times in parallel, differing by integer parameters used with non-branching pointer math into shared arrays, such as GPU-optimized Matrix multiplication or Convolutional neural network.
Reduce the overhead of acquiring a lock by first testing the locking criterion (the 'lock hint') in an unsafe manner; only if that succeeds does the actual locking logic proceed. Can be unsafe when implemented in some language/hardware combinations. It can therefore sometimes be considered an anti-pattern.
Join-pattern provides a way to write concurrent, parallel and distributed programs by message passing. Compared to the use of threads and locks, this is a high-level programming model.
Allows concurrent read access to an object, but requires exclusive access for write operations.25 An underlying semaphore might be used for writing, and a Copy-on-write mechanism may or may not be used.
A number of threads are created to perform a number of tasks, which are usually organized in a queue. Typically, there are many more tasks than threads. Can be considered a special case of the object pool pattern.
Avoiding the need for runtime concurrent mechanisms, because exclusive ownership can be proven. This is a notable capability of the Rust language, but compile-time checking isn't the only means, a programmer will often manually design such patterns into code - omitting the use of locking mechanism because the programmer assesses that a given variable is never going to be concurrently accessed.
No
—N/a
CPU atomic operation
x86 and other CPU architectures support a range of atomic instructions that guarantee memory safety for modifying and accessing primitive values (integers). For example, two threads may both increment a counter safely. These capabilities can also be used to implement the mechanisms for other concurrency patterns as above. The C# language uses the Interlocked class for these capabilities.
No
—N/a
Participants
A listing of the classes and objects used in the pattern and their roles in the design.
Collaboration
A description of how classes and objects used in the pattern interact with each other.
Consequences
A description of the results, side effects, and trade offs caused by using the pattern.
Implementation
A description of an implementation of the pattern; the solution part of the pattern.
Sample Code
An illustration of how the pattern can be used in a programming language.
Known Uses
Examples of real usages of the pattern.
Related Patterns
Other patterns that have some relationship with the pattern; discussion of the differences between the pattern and similar patterns.
In order to achieve flexibility, design patterns may introduce additional levels of indirection, which may complicate the resulting design and decrease runtime performance.
Beck draws a distinction between design patterns, which generally describe the relationships between classes, and implementation patterns, which are often limited to a single class.45 Building on this, Iglberger (2022) defines an implementation pattern as a programming idiom which does not introduce an abstraction, and so which resides at the level of implementation details.46 For this reason, they are commonly specific to the language of implementation, with copy-and-swap and RAII as examples in C++,43 although in other languages, such idioms may constitute true design patterns.47
7Baroni, A. L.; Guéhéneuc, Y. G.; Albin-Amiot, H. (June 2003). Design Patterns Formalization (Report). EMN Technical Report. Nantes: École Nationale Supérieure des Techniques Industrielles et des Mines de Nantes. S2CID624834. Academia2859481. ResearchGate277282980.
13Dougherty, C.; Sayre, K.; Seacord, R. C.; Svoboda, D.; Togashi, K. (2009). Secure Design Patterns. Software Engineering Institute, CMU. doi:10.1184/R1/6583640.v1.
14Garfinkel, Simson L. (2005). Design Principles and Patterns for Computer Systems That Are Simultaneously Secure and Usable (Ph.D. thesis). MIT. hdl:1721.1/33204.
15Díaz, P.; Rosson, M. B.; Aedo, I.; Carroll, J. M. (March 2009). "Web Design Patterns: Investigating User Goals and Browsing Strategies". In Pipek, V.; Rosson, M. B.; de Ruyter, B.; Wulf, V. (eds.). End-User Development. 2nd International Symposium on End User Development. Lecture Notes in Computer Science. Vol. 5435. Heidelberg: Springer Berlin. pp. 186–204. doi:10.1007/978-3-642-00427-8_11. ISBN 978-3-642-00427-8.
16Amshoff, B.; Dülme, C.; Echterfeld, J.; Gausemeier, J. (2015). "Business model patterns for disruptive technologies". International Journal of Innovation Management. 19 (03). Imperial College Press: 1540002. doi:10.1142/S1363919615400022. ISSN1757-5877.
17Pattern Languages of Programming, Conference proceedings (annual, 1994—) [1]
24Schmidt, Douglas C.; Stal, Michael; Rohnert, Hans; Buschmann, Frank (2000). Pattern-Oriented Software Architecture, Volume 2: Patterns for Concurrent and Networked Objects. John Wiley & Sons. ISBN 978-0-471-60695-6.
34Hannemann, Jan; Kiczales, Gregor (2002). "Design pattern implementation in Java and AspectJ". Proceedings of the 17th ACM SIGPLAN conference on Object-oriented programming, systems, languages, and applications. OOPSLA '02. pp. 161–173. doi:10.1145/582419.582436. ISBN 1-58113-471-1.
Richards, Mark; Ford, Neal (2020). Fundamentals of Software Architecture: An Engineering Approach. O'Reilly Media. ISBN 978-1-4920-4345-4.
Zheng, J.; Harper, K. E. (1 May 2010). "Concurrency design patterns, software quality attributes and their tactics". Proceedings of the 3rd International Workshop on Multicore Software Engineering. IWMSE '10. Cape Town, South Africa: Association for Computing Machinery. pp. 40–47. doi:10.1145/1808954.1808964. ISBN 978-1-60558-964-0. WikidataQ140404313.
Eloranta, Veli-Pekka; Koskinen, Johannes; Leppänen, Marko; Reijonen, Ville (2014). Designing Distributed Control Systems: A Pattern Language Approach. Wiley. ISBN 978-1-118-69415-2.
Grand, Mark (3 February 2003). Patterns in Java, Volume 1: A Catalog of Reusable Design Patterns Illustrated with UML (2nd ed.). John Wiley & Sons. ISBN 978-0-471-44933-1.
Schmidt, Douglas C.; Stal, Michael; Rohnert, Hans; Buschmann, Frank (2000). Pattern-Oriented Software Architecture, Volume 2: Patterns for Concurrent and Networked Objects. John Wiley & Sons. ISBN 978-0-471-60695-6.
A programming language is a formal language designed to express computations, typically supporting the specification of software both for humans and for computers.
In software engineering and programming language theory, the abstraction principle (or the principle of abstraction) is a basic dictum that aims to reduce duplication of information in a program…
A pattern language is an organized and coherent set of patterns, each of which describes a problem and the core of a solution that can be used in many ways within a specific field of expertise.
Data and information visualization (data viz/vis or info viz/vis) is the practice of designing and creating graphic or visual representations of quantitative and qualitative data and information with the help of static, dynamic or interactive visual items.
Set of documents providing knowledge to explain a system
Documentation is any communicable material that is used to describe, explain, or instruct regarding some attributes of an object, system, or procedure, such as its parts, assembly, installation, maintenance, and use.
Christopher Wolfgang John Alexander (4 October 1936 – 17 March 2022) was an Austrian-born British-American architect and design theorist. He was a professor at the University of California, Berkeley.
