In the field of
software engineering, the interface segregation principle (ISP) states that no code should be forced to depend on
methods
Method ( grc, μέθοδος, methodos) literally means a pursuit of knowledge, investigation, mode of prosecuting such inquiry, or system. In recent centuries it more often means a prescribed process for completing a task. It may refer to:
*Scien ...
it does not use.
[
Martin, Robert (2002). Agile Software Development: Principles, Patterns, and Practices. Pearson Education.] ISP splits
interfaces
Interface or interfacing may refer to:
Academic journals
* Interface (journal), ''Interface'' (journal), by the Electrochemical Society
* ''Interface, Journal of Applied Linguistics'', now merged with ''ITL International Journal of Applied Lin ...
that are very large into smaller and more specific ones so that clients will only have to know about the methods that are of interest to them. Such shrunken interfaces are also called ''role interface''s.
[Role Interface](_blank)
/ref> ISP is intended to keep a system decoupled and thus easier to refactor, change, and redeploy. ISP is one of the five SOLID principles of object-oriented design, similar to the High Cohesion Principle of GRASP
A grasp is an act of taking, holding or seizing firmly with (or as if with) the hand. An example of a grasp is the handshake, wherein two people grasp one of each other's like hands.
In zoology particularly, prehensility is the quality of an ap ...
.[Paulo Merson,''Principles for Microservice Design: Think IDEALS, Rather than SOLID'', The InfoQ eMag Issue #91, February 2021](_blank)
/ref>
Importance in object-oriented design
Within object-oriented design, interfaces
Interface or interfacing may refer to:
Academic journals
* Interface (journal), ''Interface'' (journal), by the Electrochemical Society
* ''Interface, Journal of Applied Linguistics'', now merged with ''ITL International Journal of Applied Lin ...
provide layers of abstraction that simplify code and create a barrier preventing coupling to dependencies.
According to many software experts who have signed the Manifesto for Software Craftsmanship, writing well-crafted and self-explanatory software is almost as important as writing working software.[Manifesto of Software Craftsmanship](_blank)
/ref> Using interfaces to further describe the intent of the software is often a good idea.
A system may become so coupled at multiple levels that it is no longer possible to make a change in one place without necessitating many additional changes.abstract class
In programming languages, an abstract type is a type in a nominative type system that cannot be instantiated directly; a type that is not abstract – which ''can'' be instantiated – is called a ''concrete type''. Every instance of an abstrac ...
can prevent this side effect.
Origin
The ISP was first used and formulated by Robert C. Martin while consulting for Xerox. Xerox had created a new printer system that could perform a variety of tasks such as stapling and faxing. The software for this system was created from the ground up. As the software grew, making modifications became more and more difficult so that even the smallest change would take a redeployment cycle of an hour, which made development nearly impossible.
The design problem was that a single Job class was used by almost all of the tasks. Whenever a print job or a stapling job needed to be performed, a call was made to the Job class. This resulted in a 'fat' class with multitudes of methods specific to a variety of different clients. Because of this design, a staple job would know about all the methods of the print job, even though there was no use for them.
The solution suggested by Martin utilized what is today called the Interface Segregation Principle. Applied to the Xerox software, an interface layer between the Job class and its clients was added using the Dependency Inversion Principle. Instead of having one large Job class, a Staple Job interface or a Print Job interface was created that would be used by the Staple or Print classes, respectively, calling methods of the Job class. Therefore, one interface was created for each job type, which was all implemented by the Job class.
Typical violation
A typical violation of the Interface Segregation Principle is given in Agile Software Development: Principles, Patterns, and Practices[Robert C. Martin,''The Interface Segregation Principle'', C++ Report, June 1996](_blank)
/ref> This example discusses the User Interface for an ATM, which handles all requests such as a deposit request, or a withdrawal request, and how this interface needs to be segregated into individual and more specific interfaces.
See also
* SOLID – the "I" in SOLID stands for Interface segregation principle
References
External links
''Principles Of OOD''
– Description and links to detailed articles on SOLID.
{{DEFAULTSORT:Interface Segregation Principle
Software design
Programming principles
Object-oriented programming