Coupling and cohesion

"Object-oriented programming has two main objectives: to build highly cohesive classes and to maintain loose coupling between those classes. High-cohesion means well-structured classes and loose coupling means more flexible, extensible software."

"Cohesive means that a certain class performs a set of closely related actions. A lack of cohesion, on the other hand, means that a class is performing several unrelated tasks. Though lack of cohesion may never have an impact on the overall functionality of a particular class or of the application itself the application software will eventually become unmanageable as more and more behaviours become scattered and end up in wrong places."

"Whenever one object interacts with another object, that is a coupling. In reality, what you need to try to minimise is coupling factors. Strong coupling means that one object is strongly coupled with the implementation details of another object. Strong coupling is discouraged because it results in less flexible, less scalable application software. However, coupling can be used so that it enables objects to talk to each other while also preserving the scalability and flexibility."

"In OO programming, coupling is unavoidable. Therefore, the goal is to reduce unnecessary dependencies and make necessary dependencies coherent."