Functional cohesion occurs when elements of a module are grouped together because they are united for a single, well-defined purpose. All of the elements in the module work together to fulfill that purpose. Functional cohesion in a module is ideal and is the highest type of cohesion.
Functional cohesion promotes the reusability of a module and makes it easier to maintain. Examples of functionally cohesive modules include one that is responsible for reading a particular file and one that is responsible for calculating shipping costs for an order.
