What is the difference between adhesion and cohesion?

Coupling and Cohesion are two key metrics in software design that determine the quality of modules.

• Coupling describes how closely connected different modules of a program are. Low coupling is preferable because it means modules are independent and changes in one module have less impact on others.

  Examples:

  • High coupling: Module A directly accesses the internal data of Module B or calls its private methods.
  • Low coupling: Modules interact through well-defined interfaces or messages.

• Cohesion describes how closely related the elements within a single module are. High cohesion is preferable because it means the elements of a module serve a single function or purpose.

  Examples:

  • Low cohesion: A module contains a set of loosely related functions performing different tasks.
  • High cohesion: A module contains functions and data that collectively perform a specific task (e.g., a module for database operations, payment processing).

Ideally, a system should have low coupling between modules and high cohesion within each module. This leads to more flexible, maintainable, and scalable code.