When performing source code review, keep coupling and cohesion in mind and ensure that the classes within a package all perform same or closely related activities (high cohesion) and that classes within different packages don't refer each other too much or at least in a well-defined manner (low coupling).
Definitions
Coupling is how inter-dependent two functional components are within your program. High coupling is bad, because if you change one function, you might end up affecting all the dependent functions as well.
Cohesion is how closely the parts within a function work together to make the function as one single, well-defined unit. High cohesion is good, since you can treat the whole function as a black box, thereby abstracting your system for better clarity.
Coupling Types
| Type (worst to best) | Description |
|---|---|
| Content/Pathological Coupling | When a module uses/alters data in another |
| Control Coupling | 2 modules communicating with a control flag (first tells second what to do via flag) |
| Common/Global-data Coupling | 2 modules communicating via global data |
| Stamp/Data-structure Coupling | Communicating via a data structure passed as a parameter. The data structure holds more information than the recipient needs. |
| Data Coupling | Communicating via parameter passing. The parameters passed are only those that the recipient needs. No data coupling : independent modules. |
Cohesion Types
| Type (worst to best) | Description |
|---|---|
| Coincidental Cohesion | Module elements are unrelated |
| Logical Cohesion | Elements perform similar activities as selected from outside module, i.e. by a flag that selects operation to perform. That is, body of function is one huge if-else/ switch on operation flag |
| Temporal Cohesion | Operations related only by general time performed |
| Procedural Cohesion | Elements involved in different but sequential activities, each on different data (usually could be trivially split into multiple modules along linear sequence boundaries) |
| Communicational Cohesion | Unrelated operations except need same data or input |
| Sequential Cohesion | Operations on same data in significant order; output from one function is input to next (pipeline) |
| Informational Cohesion | A module performs a number of actions, each with its own entry point, with independent code for each action, all performed on the same data structure. Essentially an implementation of an abstract data type |
| Functional Cohesion | All elements contribute to a single, well-defined task, i.e. a function that performs exactly one operation |
