问题
I had an interview today. I had a question from OOP, about the difference between Encapsulation & Abstraction?
I replied her to my knowledge that Encapsulation is basically to bind data members & member functions into a single unit called Class. Whereas Abstraction is basically to hide complexity of implementation & provide ease of access to the users. I thought she would be fine with my answer. But she queried, if the purpose of both are to hide information then what is the actual difference between these two? I could not give any answer to her.
Before asking this question, I read other threads on StackOverFlow about the difference between these two OOPs concepts. But I am not finding my self in a position to convince the interviewer.
Can anyone please justify it with a simplest example?
回答1:
Encapsulate hides variables or some implementation that may be changed so often in a class to prevent outsiders access it directly. They must access it via getter and setter methods.
Abstraction is used to hiding something too but in a higher degree(class, interface). Clients use an abstract class(or interface) do not care about who or which it was, they just need to know what it can do.
回答2:
This image sums pretty well the difference between both:
Source here
回答3:
Abstraction - is the process (and result of this process) of identifying the common essential characteristics for a set of objects. One might say that Abstraction is the process of generalization: all objects under consideration are included in a superset of objects, all of which possess given properties (but are different in other respects).
Encapsulation - is the process of enclosing data and functions manipulating this data into a single unit, so that to hide the internal implementation from the outside world.
This is a general answer not related to a specific programming language (as was the question). So the answer is: abstraction and encapsulation have nothing in common. But their implementations might relate to each other (say, in Java: Encapsulation - details are hidden in a class, Abstraction - details are not present at all in a class or interface).
回答4:
Abstraction: Is usually done to provide polymorphic access to a set of classes. An abstract class cannot be instantiated thus another class will have to derive from it to create a more concrete representation.
A common usage example of an abstract class can be an implementation of a template method design pattern where an abstract injection point is introduces so that the concrete class can implement it in its own "concrete" way.
see: http://en.wikipedia.org/wiki/Abstraction_(computer_science)
Encapsulation: It is the process of hiding the implementation complexity of a specific class from the client that is going to use it, keep in mind that the "client" may be a program or event the person who wrote the class.
see: http://en.wikipedia.org/wiki/Encapsulation_(object-oriented_programming)
回答5:
Encapsulation: Wrapping code and data together into a single unit. Class is an example of encapsulation, because it wraps the method and property.
Abstraction: Hiding internal details and showing functionality only. Abstraction focus on what the object does instead of how it does. It provides generalized view of classes.
int number = 5;
string aStringNumber = number.ToString();
Here, ToString() is abstraction. And how this mechanism number variable converted to string and initialize into aStringNumber is encapsulation.
Let us take a real world example of calculator. Encapsulation is the internal circuits, battery, etc., that combine to make it a calculator. Abstraction is the different buttons like on-off, clear and other buttons provided to operate it.
回答6:
There is a great article that touches on differences between Abstraction, Encapsulation and Information hiding in depth: http://www.tonymarston.co.uk/php-mysql/abstraction.txt
Here is the conclusion from the article:
Abstraction, information hiding, and encapsulation are very different, but highly-related, concepts. One could argue that abstraction is a technique that helps us identify which specific information should be visible, and which information should be hidden. Encapsulation is then the technique for packaging the information in such a way as to hide what should be hidden, and make visible what is intended to be visible.
回答7:
difference in both is just the View Point
Encapsulation word is used for hiding data if our aim is to prevent client seeing inside view of our logic
Abstraction word is used for hiding data if our aim is to show our client a out side view
Outside view means that let suppose
BubbleSort(){
//code
swap(x,y);
}
here we use swap in bubble sort for just showing our client what logic we are applying, If we replace swap(x,y) with whole code here, In a single instance he/she can't understand our logic
回答8:
Encapsulation:
Hiding something, sort of like medicine capsule. We don't know what is in the capsule, we just take it. Same as in programming - we just hide some special code of method or property and it only gives output, same as capsule. In short, encapsulation hides data.
Abstraction:
Abstraction means hiding logic or implementation. For example, we take tablets and see their color and but don't know what is the purpose of this and how it works with the body.
回答9:
Abstraction
In Java, abstraction means hiding the information to the real world. It establishes the contract between the party to tell about “what should we do to make use of the service”.
Example, In API development, only abstracted information of the service has been revealed to the world rather the actual implementation. Interface in java can help achieve this concept very well.
Interface provides contract between the parties, example, producer and consumer. Producer produces the goods without letting know the consumer how the product is being made. But, through interface, Producer let all consumer know what product can buy. With the help of abstraction, producer can markets the product to their consumers.
Encapsulation:
Encapsulation is one level down of abstraction. Same product company try shielding information from each other production group. Example, if a company produce wine and chocolate, encapsulation helps shielding information how each product Is being made from each other.
- If I have individual package one for wine and another one for chocolate, and if all the classes are declared in the package as default access modifier, we are giving package level encapsulation for all classes.
- Within a package, if we declare each class filed (member field) as private and having a public method to access those fields, this way giving class level encapsulation to those fields
回答10:
Yes, it is true that Abstraction and Encapsulation are about hiding.
Using only relevant details and hiding unnecessary data at Design Level is called Abstraction. (Like selecting only relevant properties for a class 'Car' to make it more abstract or general.)
Encapsulation is the hiding of data at Implementation Level. Like how to actually hide data from direct/external access. This is done by binding data and methods to a single entity/unit to prevent external access. Thus, encapsulation is also known as data hiding at implementation level.
回答11:
Abstraction: what are the minimum functions and variables that should be exposed to the outside of our class.
Encapsulation: how to achieve this requirement, meaning how to implement it.
回答12:
Just a few more points to make thing clear,
One must not confuse data abstraction and the abstract class. They are different.
Generally we say abstract class or method is to basically hide something. But no.. That is wrong. What is the word abstract means ? Google search says the English word abstraction means
"Existing in thought or as an idea but not having a physical or concrete existence."
And thats right in case of abstract class too. It is not hiding the content of the method but the method's content is already empty (not having a physical or concrete existence) but it determines how a method should be (existing in thought or as an idea) or a method should be in the calss.
So when do you actually use abstract methods ?
- When a method from base class will differ in each child class that extends it.
- And so you want to make sure the child class have this function implemented.
- This also ensures that method, to have compulsory signature like, it must have n number of parameters.
So about abstract class! - An Abstract class cannot be instantiated only extended! But why ?
- A class with abstract method must be prevented from creating its own instance because the abstract methods in it, are not having any meaningful implementation.
- You can even make a class abstract, if for some reason you find that it is meaning less to have a instance of your that class.
An Abstract class help us avoid creating new instance of it!
An abstract method in a class forces the child class to implement that function for sure with the provided signature!
来源：https://stackoverflow.com/questions/15176356/difference-between-encapsulation-and-abstraction