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We know in java, encapsulation is a process of wrapping up of code data together into a single unit or hiding the data. Can anybody let me know from whom we are hiding the data?
You are "hiding" data from users of your object that should be able to use it without needing to know about its internals.
The main reason for this is to allow you to later change these internals without breaking the code that calls into your object.
This is a technique to improve software maintainability.
Common misconception: It should definitely not be seen as a security measure (in the sense that it protects sensitive data from malicious actors that should not be allowed to gain access to it -- encapsulation does no such thing).
Data hiding is a software development technique specifically used in object-oriented programming (OOP) to hide internal object details (data members). Data hiding ensures exclusive data access to class members and protects object integrity by preventing unintended or intended changes.
Data hiding also reduces system complexity for increased robustness by limiting interdependencies between software components.
That's why Data hiding is also known as data encapsulation or information hiding.
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One of my professor said: "If we consider that, if constraints are sometimes completely avoided and therefore not defined in some database of some project, it is only at the application level that we can manage data integrity."
In which condition can we avoid constraints on database? Please I need your help
You should ask your professor to clarify their statements, not Stack Overflow.
It's appropriate to use database constraints in many cases.
For example, consider a case where a single database is used by multiple applications. If you were to enforce data integrity in the application, then you would have to implement the data integrity rules multiple times, perhaps even in different programming languages if the client apps are written in different languages. If you don't implement the data integrity logic with the same behavior in all apps, then you might create data in one app that is invalid for the other apps.
Whereas if you implement data integrity constraints in the database, then all apps must conform to a single set of constraints. Data will be valid for all apps, and there's no chance of anomalies. This is a good thing.
There are exceptions to every rule, of course, but in general it's a good idea to implement logic in one place. This is sometimes referred to as the DRY principle of software design, i.e. Don't Repeat Yourself.
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I'm almost new to programming and I came to this question that:
why should object carry code along with data? isn't packing data enough?
For example:
Instead of having 5 employee objects that each has a getDataOfBirth() method (consuming more memory), have a single method in global space and have 5 object with only attributes(smaller objects).
Am I getting something wrong? Is my question even considered general and possible to be occurred in every newbie's mind?
The linguistic aspect of it:
This is an idea that OOP skeptics have been talking about for a long time, but it's more of a matter of preference I would say. If you are new to programming and already are thinking about these things, then maybe functional programming would make a lot of sense to you.
The memory aspect of it:
The functions are typically not stored inside the objects, so OO objects that have a lot of functions do typically not carry those functions around. This is however an implementation detail but most OOP languages should be thought of like that.
Especially in the case of natively compiled languages like C++, the code and the data will be separated into different memory areas altogether and will not really mix. That is also a bit of an implementation detail but all mainstream operating systems, as far as I know, will allocate memory with code separated from data. The functions of a class will be allocated in one area and the data of the objects in another, and normally all objects of the same class will use the same functions.
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The facade pattern is to provide a simplified interface for complex code.
Therefore, it is correct to use it as a wrapper for a system? That would be like a translation map for facilitating the understanding hiding the complexity?
Is it correct then call all Facade as API?
Well the programming interface into any application is the Application Programming Interface, so yes it would be an API, in the same way that your OS has an API keeping you from fiddling with too much memory or abstracting the hard drive - or a game engine has an API acting as a facade for graphics and audio code.
So yes, the implementation of a Facade is an API, but so is any other code which you use as an interface into a more complicated system. (I guess you could ask the question as "are all APIs a facade that just provides a layer of abstraction?" - and you could probably make the argument that it's true).
It's a bit of an odd question to consider however, because depending on who you talk to, these terms may change - we only really use them to represent the idea of abstraction, as we see fit.
Remember that design patterns are not hard fast rules. A Facade is an API that reduces the complexity of using some system. That system may be a single library, multiple libraries, various network clients, etc.
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I always hear that we need to encapsulate whenever we write object-oriented code. If I'm the only developer on a project, do I still need to use encapsulation?
One way to put an answer: Encapsulation, conceptually, exists for writing better, safer, less error-prone code. It doesn't exist, primarily, to facilitate teams working together on code (that might be a side effect, but that's not the purpose).
So the goods that encapsulation seeks to foster scale from one coder to many coders, and they are goods that do not really have to do with the number of coders, although those goods may find stronger expression the larger the project and teams are.
Encapsulation is there for a reason.
Someone has to maintain and manage your code after you are done, right? What if the project gets bigger and you get team members?
So, the answer is "yes", it is always best to use encapsulation whenever possible.
The fact you are asking this question makes me wonder you actually did not get the actual value of encapsulation as a means to reduce and thus deal with complexity.
My theoretical computer science professor used to tell me that in the end, if you think at the whole binary representation of a program, any program is just a number. Very big indeed but, only a number. And that is true, any other construct we use but 0 and 1 (i.e. C++, Java, Python, functional programming, object oriented programming, aspect oriented programming, etc..) is just because of the fact we need more abstract means to get the one number we need.
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After reading the definition of procedural design (http://en.wikipedia.org/wiki/Design_document) and searching for a few example diagrams, I have been having trouble on finding out more on what procedural design means other than finding this diagram (http://www.kelso.scotborders.sch.uk/departments/computing/resources/mindmaps/Procedural%20program%20design.gif). Typically, when is this type of documentation necessary? Is it when there's a specific algorithm used in the application?
This is most often used when you have a few very similar constructs that are used really often. In a way SQL is a "procedural design" since it limits you to tables and column and a handful of operations which can be applied to the "data model" (= the database).
Code generators thrive in this area since they have a large but simple input and generate a lot of code that would be extremely tedious and error prone to write by hand. In a similar way, you can generate "documentation" for this which is usually a big waste of time since it will be enormous in volume and contain very little information about how the system works.
[EDIT] In computer science the amount of information in a message is the amount of "surprise" you get per bit. So one page of "1'000 feet view" which is tight packed with information, which gives you a compressed introduction how the system is designed and how you can find your way around, is worth more than 1'000 pages of documentation generated from a data model.