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

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.