Editing Cohesion (computer science) (section)

== High cohesion ==
{{refimprove section|date=May 2023}}
In [[object-oriented programming]], a class is said to have high cohesion if the methods that serve the class are similar in many aspects.<ref name="Marsic_2012"/> In a highly cohesive system, code readability and [[reusability]] is increased, while complexity is kept manageable.
[[File:CouplingVsCohesion.svg|thumb|Cohesion]]
Cohesion is increased if:
*The functionalities embedded in a class, accessed through its methods, have much in common.
*Methods carry out a small number of related activities, by ''avoiding'' [[Granularity#Data granularity|coarsely grained]] or unrelated sets of data.
*Related methods are in the same source file or otherwise grouped together; for example, in separate files but in the same sub-directory/folder.

Advantages of high cohesion (or "strong cohesion") are:
*Reduced module complexity, with fewer operations.
*Increased system [[maintainability]], because logical changes in the domain affect fewer modules, and changes in one module require fewer changes in other modules.
*Increased module reusability, because application developers will find the [[Software component|component]] they need more easily among the cohesive set of operations provided by the module.

While in principle a module can have perfect cohesion by only consisting of a single, atomic element – having a single function, for example – in practice complex tasks are not expressible by a single, simple element. Thus a single-element module has an element that is either too complicated to accomplish a task, or too narrow and thus tightly [[Coupling (computer programming)|coupled]] to other modules. Thus cohesion is balanced with both unit complexity and coupling.