principles:high_cohesion
Differences
This shows you the differences between two versions of the page.
Both sides previous revisionPrevious revisionNext revision | Previous revisionNext revisionBoth sides next revision | ||
principles:high_cohesion [2013-02-12 21:43] – [Strategies] christian | principles:high_cohesion [2020-10-12 16:15] – old revision restored (2019-05-29 14:47) 159.69.186.191 | ||
---|---|---|---|
Line 6: | Line 6: | ||
===== Context ===== | ===== Context ===== | ||
/* fill in contexts here: */ | /* fill in contexts here: */ | ||
- | * [[contexts: | + | * [[contexts: |
+ | * [[contexts: | ||
+ | * [[contexts: | ||
Line 18: | Line 20: | ||
The cohesion of a module is a measure for how well the internal parts of a module (e.g. the methods and attributes of a class) belong together. Having a high cohesion means, that a module should only comprise responsibilities which belong together. | The cohesion of a module is a measure for how well the internal parts of a module (e.g. the methods and attributes of a class) belong together. Having a high cohesion means, that a module should only comprise responsibilities which belong together. | ||
- | Several kinds of cohesion can be distinguished some of which are strong and some of which are loose. So strong forms of coupling should be preferred: FIXME add explanation of cohesion types | + | Several kinds of cohesion can be distinguished some of which are strong and some of which are loose. So strong forms of coupling should be preferred. |
===== Rationale ===== | ===== Rationale ===== | ||
Line 27: | Line 29: | ||
* Divide one large module into several smaller but more cohesive ones | * Divide one large module into several smaller but more cohesive ones | ||
+ | |||
+ | ===== Caveats ===== | ||
+ | |||
+ | See section [[#contrary principles]]. | ||
+ | |||
+ | |||
===== Origin ===== | ===== Origin ===== | ||
- | /* the *primary* source */ | ||
+ | W. P. Stevens, G. van Niekerk, G. J. Myers, L. L. Constantine: | ||
===== Evidence ===== | ===== Evidence ===== | ||
Line 35: | Line 43: | ||
/ | / | ||
- | * [[wiki: | + | * [[wiki: |
- | * [[wiki: | + | * [[wiki: |
/ | / | ||
Line 47: | Line 55: | ||
==== Specializations ==== | ==== Specializations ==== | ||
- | * [[Tell don't Ask/ | ||
* [[Constantine' | * [[Constantine' | ||
* [[Single Responsibility Principle]] (SRP): SRP is a stronger version of HC. | * [[Single Responsibility Principle]] (SRP): SRP is a stronger version of HC. | ||
Line 61: | Line 68: | ||
==== Complementary Principles ==== | ==== Complementary Principles ==== | ||
+ | * [[Tell don't Ask/ | ||
* [[Encapsulate the Concept that Varies]] (ECV): Adhering to HC often results in modules to be split up into several more cohesive ones. ECV gives further advice on how to do that. | * [[Encapsulate the Concept that Varies]] (ECV): Adhering to HC often results in modules to be split up into several more cohesive ones. ECV gives further advice on how to do that. | ||
Line 69: | Line 77: | ||
- | ===== Example | + | ===== Examples |
Line 77: | Line 85: | ||
/ | / | ||
/ | / | ||
+ | |||
+ | ==== Class level cohesion ==== | ||
+ | |||
+ | Robert Cecil Martin (Uncle Bob) describes maximal cohesion at class level as "a class in which each variable is used by each method" | ||
+ | |||
+ | "In general the more variables a method manipulates the more cohesive that method is to its class." | ||
+ | (Clean Code: A Handbook of Agile Software Craftsmanship - Chapter 10) | ||
===== Further Reading ===== | ===== Further Reading ===== | ||
- | * Albert Endres and Dieter Rombach: //A Handbook of Software and Systems Engineering// | + | * Albert Endres and Dieter Rombach: //[[resources: |
* [[wp> | * [[wp> | ||
* [[wiki> | * [[wiki> | ||
+ | * {{page> | ||
+ | |||
+ | ===== Discussion ===== | ||
+ | Discuss this wiki article and the principle on the corresponding [[talk: |
principles/high_cohesion.txt · Last modified: 2021-10-18 21:36 by christian