What does 'low in coupling and high in cohesion' mean

Question

I have problems understanding the statement low in coupling and high in cohesion. I have googled and read a lot about this, but still finding it hard to underst

Answer 1

What I believe is this:

Cohesion refers to the degree to which the elements of a module/class belong together, it is suggested that the related code should be close to each other, so we should strive for high cohesion and bind all related code together as close as possible. It has to do with the elements within the module/class.

Coupling refers to the degree to which the different modules/classes depend on each other, it is suggested that all modules should be independent as far as possible, that's why low coupling. It has to do with the elements among different modules/classes.

To visualize the whole picture will be helpful:

The screenshot was taken from Coursera.

Answer 2

Cohesion - how closely related everything is with one another.
Coupling - how everything is connected to one another.

Let's take an example - We want to design a self-driving car.

(1) We need the motor to run properly.

(2) We need the car to drive on its own.

All of the classes and functions in (1) starting the motor and making it run work great together, but do not help the car steer. So we place those classes behind an Engine Controller.

All of the classes and functions in (2) work great to make the car steer, accelerate and brake. They do not help the car start or send gasoline to the pistons. So we place these classes behind its own Driving Controller.

These controllers are used to communicate with all of the classes and functions that are available. The controllers then communicate only with each other. This means I can't call a function in the piston class from the gas pedal class to make the car go faster.

The pedal class has to ask the Driving Controller to talk to the Engine Controller which then tells the piston class to go faster. This allows us programmers to be able to find issues and allows us to combine large programs without worrying. This is because the code was all working behind the controller.

Answer 3

An example might be helpful. Imagine a system which generates data and puts it into a data store, either a file on disk or a database.

High Cohesion can be achieved by separate the data store code from the data production code. (and in fact separating the disk storage from the database storage).

Low Coupling can be achieved by making sure that the data production doesn't have any unnecessary knowledge of the data store (e.g. doesn't ask the data store about filenames or db connections).

Answer 4

Low Coupling and High Cohesion is a recommended phenomenon.

Coupling means to what extent various modules are interdependent and how the other modules are affected on changing some/considerable functionality of a module. Low coupling is emphasized as the dependency has to be maintained low so that very least/negligible changes are made to other modules.

Answer 5

Cohesion in software engineering, as in real life, is how much the elements consisting a whole(in our case let's say a class) can be said that they actually belong together. Thus, it is a measure of how strongly related each piece of functionality expressed by the source code of a software module is.

One way of looking at cohesion in terms of OO is if the methods in the class are using any of the private attributes.

Now the discussion is bigger than this but High Cohesion (or the cohesion's best type - the functional cohesion) is when parts of a module are grouped because they all contribute to a single well-defined task of the module.

Coupling in simple words, is how much one component (again, imagine a class, although not necessarily) knows about the inner workings or inner elements of another one, i.e. how much knowledge it has of the other component.

Loose coupling is a method of interconnecting the components in a system or network so that those components, depend on each other to the least extent practically possible…

I wrote a blog post about this. It discusses all this in much detail, with examples etc. It also explains the benefits of why you should follow these principles.

Answer 6

Long story short, low coupling as I understood it meant components can be swapped out without affecting the proper functioning of a system. Basicaly modulize your system into functioning components that can be updated individually without breaking the system