| name | apply-high-cohesion |
| description | Use when assigning responsibilities to classes — especially when a class is hard to name, does work unrelated to its core concept, or a single change requires understanding an entire class to avoid breaking something. |
| source | Craig Larman, "Applying UML and Patterns", 3rd ed., Prentice Hall, 2004 |
| tags | ["grasp","high-cohesion","design-principles","oop","responsibility-assignment","developer","readability","maintainability"] |
| related | ["apply-low-coupling","apply-information-expert","apply-solid-principles","apply-unix-philosophy"] |
Apply High Cohesion
Assign responsibilities so that each class remains focused on one strongly related set of concerns that can be understood and explained as a unit.
Why This Is Best Practice
Adopted by: GRASP (Larman, 2004); SOLID SRP (Martin, 2003); Unix philosophy; Go standard library design (small, focused interfaces). High cohesion is a foundational metric in software quality measurement — Chidamber & Kemerer (1994, IEEE TSE) established the Lack of Cohesion of Methods (LCOM) metric, now a standard quality gate in SonarQube, CodeClimate, and NDepend.
Impact: Chidamber & Kemerer (1994) showed that LCOM is inversely correlated with fault-proneness — low-cohesion classes have statistically higher defect density. Palomba et al. (2018, IEEE TSE) confirmed that God Classes (the archetypal low-cohesion pattern) have 3–4x higher change frequency than average classes. High-cohesion classes are self-documenting: the class name describes everything inside it.
Low cohesion grows through feature accretion — each new feature lands in the nearest existing class rather than the right class. The result is a God Class that knows everything and changes for every reason. High cohesion is not achieved by refusing to add features; it is achieved by asking "does this feature belong here, or in a focused class I haven't created yet?" The distinction between High Cohesion (GRASP) and SRP (SOLID) is axis: SRP asks "how many actors would cause this to change?"; High Cohesion asks "how related are the operations this class performs?"
