Skip to main content

Encapsulation

Encapsulation and information hiding are often used interchangeably. But they are actually different. Information hiding is a design principle, whereas encapsulation is a language facility.
Encapsulation is the process of bundling code and the data it acts on together in one entity. David Parnas describes information hiding as "hiding of critical design decisions", so that the client code does not have to understand the intricacies of the design, and is also oblivious to any changes in design. Encapsulation can happen without information hiding, but will not be effective.
Encapsulation facilitates, but does not guarantee information hiding. Following some simple guidelines will help us create better classes

  • Encapsulation rule 1: Place data and the operations that perform on that data in the same class

  • Encapsulation rule 2: Use responsibility-driven design to determine the grouping of data and operations into classes



  • Information hiding rule 1: Don't expose data items

  • Information hiding rule 2: Don't expose the difference between stored data and derived data

  • Information hiding rule 3: Don't expose a class's internal structure

  • Information hiding rule 4: Don't expose implementation details of a class





  • Read this Javaworld article to better understand these concepts.




    Reflections

    1. Why do we need encapsulation?
    2. Can an OO language exist without encapsulation?




    Note: This post was originally posted on my blog at http://www.adaptivelearningonline.net
    Here are the comments from the old blog post


    COMMENT:
    AUTHOR: Amol Chaudhari

    Hi Parag,
    The article on javaworld - "Encapsulation is not information Hiding" is very insightful. Thanks a lot for providing us such a good link.
    Prior to reading this article, i never thought of consequences my bad Class design could make. Besides pointing out the subtle differences between encapsulation and information hiding, Paul Rogers has given hints regarding the class organization also, like placing the class variables at the bottom and getters/setters at top makes you focus on the responsibilities of the class rather than the internal data structure. He also hints on the possible choice of method names, like using getPosition() rather using getPositionArray().



    COMMENT:
    AUTHOR: Parag

    Hi Amol,

    Thanks for the feedback. I am glad you liked the article. Encapsulation is an often misunderstood concept. I especially liked the example of how making an array member private but exposing the fact that the collection is actually an array breaks the concept of information hiding.

    Design decisions do have very real implications. Bad design always accumalates what we call design debt, which has to be paid off at some point of time.



    COMMENT:
    AUTHOR: Rashmi

    Although we often see the terms 'Encaptulation' and 'Data Hiding' in all OOP articles but often fail to provide a difference between them in terms of a defination.This article was a great help.
    Sir it would be very useful if you could explain the rules for information hiding through a code in java



    COMMENT:
    AUTHOR: Parag

    Rashmi,
    Thanks for your suggestion. I will update the post soon with a code example.

    Comments

    Anonymous said…
    Hi Parag,
    The post is really helpful for understanding one of the core OOP concept.

    I think there should be some visual element to this post which people could remember this distinction always.

    In my blog ,I had tried to do the same in explaination of Abstraction and Encapsulation.

    http://lalitkale.wordpress.com/2008/02/10/difference-between-abstraction-and-encapsulation/

    I would appreciate,If you could comment on my understading about these two concepts.

    Popular posts from this blog

    Running your own one person company

    Recently there was a post on PuneTech on mom's re-entering the IT work force after a break. Two of the biggest concerns mentioned were : Coping with vast advances (changes) in the IT landscape Balancing work and family responsibilities Since I have been running a one person company for a good amount of time, I suggested that as an option. In this post I will discuss various aspects of running a one person company. Advantages: You have full control of your time. You can choose to spend as much or as little time as you would like. There is also a good chance that you will be able to decide when you want to spend that time. You get to work on something that you enjoy doing. Tremendous work satisfaction. You have the option of working from home. Disadvantages: It can take a little while for the work to get set, so you may not be able to see revenues for some time. It takes a huge amount of discipline to work without a boss, and without deadlines. You will not get the benefits (insuran

    Some thoughts on redesigning education

    Some time back I read a blog post on redesigning education. It asked some very good questions. Stuff which I had been thinking of myself. I left my thoughts on the blog, but I would also like to start a conversation around these ideas with those who read this blog as well. I would like to know what other people think of the issue of redesigning (college) education. I have often thought about how college education can be improved. To answer this question, we first have to ask a very basic question. What is the purpose of education? To me, we need education for 3 things: To learn more about the world around us To lead positive constructive lives To earn a good living / fulfill our ambitions I think education has to a large extent evolved to fulfill #3 (with a bias towards earning a comfortable living). The semester system, along with multiple choice tests, and grading, has made our education system into an assembly line. Students are pushed into the assembly line, given classes, admini

    Testing Groovy domain classes

    If you are trying to test Grails domain class constraints by putting your unit test cases in the 'test/unit' directory, then your tests will fail because the domain objects will not have the 'valdate' method. This can be resolved in two ways: Place the test cases inside test/integration (which will slow things down) Use the method 'mockForConstraintsTests(Trail)' to create mock method in your domain class and continue writing your test cases in 'test/unit' What follows is some example code around this finding. I am working on a Groovy on Grails project for a website to help programmers keep up and refresh their skills. I started with some domain classes and then moved on to write some unit tests. When we create a Grails project using grails create-app , it creates several directories, one of which is a directory called 'test' for holding unit tests. This directory contains two directories, 'unit', and 'integration' for uni