Cohesion and Coupling deal with the quality of an OO design. Generally, good OO design should be loosely coupled and highly cohesive. Lot of the design principles, design patterns which have been created are based on the idea of “Loose coupling and high cohesion”.

The aim of the design should be to make the application:

  • easier to develop
  • easier to maintain
  • easier to add new features
  • less Fragile.

Coupling:

Coupling is the degree to which one class knows about another class. Let us consider two classes class A and class B. If class A knows class B through its interface only i.e it interacts with class B through its API then class A and class B are said to be loosely coupled.

If on the other hand class A apart from interacting class B by means of its interface also interacts through the non-interface stuff of class B then they are said to be tightly  coupled. Suppose the developer changes the class B‘s non-interface part i.e non API stuff then in case of loose coupling class A does not breakdown but tight coupling causes the class A to break.

So its always a good OO design principle to use loose coupling between the classes i.e all interactions between the objects in OO system should use the APIs. An aspect of good class and API design is that classes should be well encapsulated.

Another related thoughts on Coupling.

Cohesion:

Cohesion is used to indicate the degree to which a class has a single, well-focused purpose. Coupling is all about how classes interact with each other, on the other hand cohesion focuses on how single class is designed. Higher the cohesiveness of the class, better is the OO design.

Benefits of Higher Cohesion:

  • Highly cohesive classes are much easier to maintain and less frequently changed.
  • Such classes are more usable than others as they are designed with a well-focused purpose.

Single Responsibility principle aims at creating highly cohesive classes.

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About The Author

Mohamed Sanaulla

35 Responses to Cohesion and Coupling: Two OO Design Principles

  1. Gareth says:

    Very good summary of cohesion and coupling

  2. Gareth,

    Thanks for the feedback!

  3. Sergiu V says:

    Nice article. Thank you.

  4. […] strongly associated code together (cohesion/coupling principle), and put a comment above it mentioning it’s intent. Separate these blocks of code from other […]

  5. jetti says:

    Thanks for giving more and understandable about coupling and cohesion…

  6. Many thanks for the clear explanation of both principles.

  7. yuva says:

    well explained !

  8. Ahmed says:

    Very Special Definitions of both never find on other links, Thanks a lot !

  9. Murali Krishna.S says:

    hi thanks for explaining this 2 principles very clearly..and i feel very easy to understand

  10. arun kumar says:

    txxxxxxxxx a lot a very good explanation

  11. Dilip says:

    Very well explained!! :)

  12. […] had previously written a post related to coupling and cohesion here and that was more of a basic definition of both the […]

  13. Manav says:

    very helpful explanation…. :)

  14. Jagat says:

    Found this on stack overflow. Good job sanaulla.

  15. Ankit says:

    Nice, simple and straight explanation.
    Good article!

  16. John says:

    Sorry, I do not understand. You did not include a simple example which clearly shows the concept. I don’t think that this answer will satisfy any knowledgeable and experienced interviewer.

  17. saloni jhanwar says:

    Copy paste for K&B, Do some real work then cheap ctrl+c ctrl+v

  18. rafat says:

    hi brother mohamed
    i want to know how i can measure the coupling and cohesion for set of software variants for example 10 products

  19. manoj says:

    Nice post.Really it has a value .

    Thank you sir.

  20. Sagar says:

    Mohamed, the explanation is very clear.. Thank you.. :)

  21. dhanveerhasan@gmail.com says:

    nice ….very wonder full……i and this concept loosely coupled each other

  22. AQSA says:

    Both concepts are difficult but due to this article i understand thes concepts.thankssss

  23. Amir says:

    Best article found on the web about cohesion and coupling

  24. Shahid says:

    Hi.. good article but whats missing is . try and implement it with some code and than explain so that it will be easy for any1 to understand these concepts..

  25. Ashwani jain says:

    was easy and quick to grasp… just need to have some code examples..

  26. dream says:

    Thanks for a good explanation. Became simple to understand. Coupling (Married couples will be tightly coupled (have issues) if they know non-interface stuff)

  27. pooja joshi says:

    easy explanations.

  28. CodeNewbie says:

    very straight forward thank you very much

  29. techbrainless says:

    Awesome explanation. Thanks a lot Mr. Sanaulla.

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