class interview questions
Top class frequently asked interview questions
Is it possible to have static class variables or methods in python? What syntax is required to do this?
Source: (StackOverflow)
What is the difference between old style and new style classes in Python? Is there ever a reason to use old-style classes these days?
Source: (StackOverflow)
What is the purpose of the self word in Python? I understand it refers to the specific object created from that class, but I can't see why it explicitly needs to be added to every function as a parameter. To illustrate, in Ruby I can do this:
class myClass
def myFunc(name)
@name = name
end
end
Which I understand, quite easily. However in Python I need to include self:
class myClass:
def myFunc(self, name):
self.name = name
Can anyone talk me through this? It is not something I've come across in my (admittedly limited) experience.
Source: (StackOverflow)
I prefer to use OOP in large scale projects like the one I'm working on right now. I need to create several classes in JavaScript but, if I'm not mistaken, there are at least a couple of ways to go about doing that. What would be the syntax and why would it be done in that way?
I would like to avoid using third-party libraries - at least at first.
Looking for other answers, I found the article Object-Oriented Programming with JavaScript, Part I: Inheritance - Doc JavaScript that discusses object-oriented programming in JavaScript. Is there a better way to do inheritance?
Source: (StackOverflow)
This question already has an answer here:
Here's what MSDN has to say under When to Use Static Classes:
static class CompanyInfo
{
public static string GetCompanyName() { return "CompanyName"; }
public static string GetCompanyAddress() { return "CompanyAddress"; }
//...
}
Use a static class as a unit of
organization for methods not
associated with particular objects.
Also, a static class can make your
implementation simpler and faster
because you do not have to create an
object in order to call its methods.
It is useful to organize the methods
inside the class in a meaningful way,
such as the methods of the Math class
in the System namespace.
To me, that example doesn't seem to cover very many possible usage scenarios for static classes. In the past I've used static classes for stateless suites of related functions, but that's about it. So, under what circumstances should (and shouldn't) a class be declared static?
Source: (StackOverflow)
How do you create a static class in C++? I should be able to do something like:
cout << "bit 5 is " << BitParser::getBitAt(buffer, 5) << endl;
Assuming I created the BitParser class. What would the BitParser class definition look like?
Source: (StackOverflow)
For documenting classes with roxygen(2), specifying a title and description/details appears to be the same as for functions, methods, data, etc. However, slots and inheritance are their own sort of animal. What is the best practice -- current or planned -- for documenting S4 classes in roxygen2?
Due Diligence:
I found mention of an @slot tag in early descriptions of roxygen.
A 2008 R-forge mailing list post
seems to indicate that this is dead,
and there is no support for @slot in roxygen:
Is this true of roxygen2? The previously-mentioned post suggests a user should instead make their own itemized list with LaTeX markup. E.g. a new S4 class that extends the "character" class would be coded and documented like this:
#' The title for my S4 class that extends \code{"character"} class.
#'
#' Some details about this class and my plans for it in the body.
#'
#' \describe{
#' \item{myslot1}{A logical keeping track of something.}
#'
#' \item{myslot2}{An integer specifying something else.}
#'
#' \item{myslot3}{A data.frame holding some data.}
#' }
#' @name mynewclass-class
#' @rdname mynewclass-class
#' @exportClass mynewclass
setClass("mynewclass",
representation(myslot1="logical",
myslot2="integer",
myslot3="data.frame"),
contains = "character"
)
However, although this works, this \describe , \item approach for documenting the slots seems inconsistent with the rest of roxygen(2), in that there are no @-delimited tags and slots could go undocumented with no objection from roxygenize(). It also says nothing about a consistent way to document inheritance of the class being defined. I imagine dependency still generally works fine (if a particular slot requires a non-base class from another package) using the @import tag.
So, to summarize, what is the current best-practice for roxygen(2) slots?
There seem to be three options to consider at the moment:
- A -- Itemized list (as example above).
- B --
@slot ... but with extra tags/implementation I missed. I was unable to get @slot to work with roxygen / roxygen2 in versions where
it was included as a replacement for the itemized list in the example
above. Again, the example above does work with roxygen(2).
- C -- Some alternative tag for specifying slots, like
@param, that would accomplish the same thing.
I'm borrowing/extending this question from a post I made to the roxygen2 development page on github.
Source: (StackOverflow)
We're often told we should protect encapsulation by making getter and setter methods (properties in C#) for class fields, instead of exposing the fields to the outside world.
But there are many times when a field is just there to hold a value and doesn't require any computation to get or set. For these we would all do this number:
public class Book
{
private string _title;
public string Title
{
get{ return _title; }
set{ _title = value; }
}
}
Well, I have a confession, I couldn't bear writing all that (really, it wasn't having to write it, it was having to look at it), so I went rogue and used public fields.
Then along comes C# 3.0 and I see they added automatic properties:
public class Book
{
public string Title {get; set;}
}
which is tidier, and I'm thankful for it, but really, what's so different than just making a public field?
public class Book
{
public string Title;
}
Source: (StackOverflow)
I am learning the ropes in Python. When I try to print an object of class Foobar using the print() function, I get an output like this:
<__main__.Foobar instance at 0x7ff2a18c>
Is there a way I can set the printing behaviour (or the string representation) of a class and its objects? For instance, when I call print() on a class object, I would like to print its data members in a certain format. How to achieve this in Python?
If you are familiar with C++ classes, the above can be achieved for the standard ostream by adding a friend ostream& operator << (ostream&, const Foobar&) method for the class.
Source: (StackOverflow)
I'm used to the Java model where you can have one public class per file. Python doesn't have this restriction, and I'm wondering what's the best practice for organising classes.
Source: (StackOverflow)
This question was already asked in the context of C#/.Net.
Now I'd like to learn the differences between a struct and a class in C++. Please discuss the technical differences as well as reasons for choosing one or the other in OO design.
I'll start with an obvious difference:
- If you don't specify
public: or private:, members of a struct are public by default; members of a class are private by default.
I'm sure there are other differences to be found in the obscure corners of the C++ specification.
Source: (StackOverflow)
Is there any reason for a class declaration to inherit from object?
I just found some code that does this and I can't find a good reason why.
class MyClass(object):
# class code follows...
Source: (StackOverflow)
What's the difference between struct and class in .NET?
I'm looking for a clear, concise and accurate answer. Ideally as the actual answer, although links to good explanations are welcome.
Source: (StackOverflow)
I'm just going over some Scala tutorials on the Internet and have noticed in some examples an object is declared at the start of the example.
What is the difference between class and object in Scala?
Source: (StackOverflow)