Part 18 - C# Tutorial - Namespaces.avi Video Lecture | C sharp: Enhance your Skills (English) - Back-End Programming

hello welcome to prison technologies I
am Beckett this is part 18 namespaces
and c-sharp in this session we will
learn the basics around namespaces using
alias directives at different namespace
members now why namespaces what is the
advantage of using namespaces they're
basically two main advantages of using
namespaces they help you organize your
programs and also they provide
assistance in avoiding name clashes
especially in very large projects so
what do we mean by that let's look at an
example now let's say I am working on
you know a project and let's say the
project name is project a and let's say
I have two teams team a and Team B have
these two teams working on this project
a now I want all the classes that are
developed by team a to be presented
projected or team a namespace so that
just by looking at the name of the class
I can identify which team has developed
that similarly I want all the glasses
developed by TV to be present in a
namespace project a dot Team B in many
projects actually based on the function
let's say for example I have a job
portal project that I'm working on in
job poodles
you know usually we have candidates you
know basically job seekers and your
providers you know all the classes that
are related to job seekers probably you
know might be they might be present end
job butl dot jobseekers namespace
whereas all the classes that are related
to your providers may be present in job
buddhahood job providers namespace so
basically namespaces help you to
organize your code okay before we look
at an example have to do that you know
let's understand you know we let us
understand how Microsoft is actually
using namespaces now even Microsoft is
using namespaces to organize their code
for example from class one from session
one we have been using this console
class a console dot write line
let's say we want to print hello okay so
if you look at this class comes whole
class where is this coming from
this is coming from you know if I
right-click on that class and say go to
definition the canceled class is
actually coming from the system
namespace okay which is present in
system assembly okay so the console
class is coming from the system
namespace now similarly you know just
like how Microsoft is using namespaces
to organize the code we can create you
know namespaces to organize the classes
that we create you know going with the
example that we have discussed you know
let's say I'm I'm working with two
themes project called project a and I
want all the class related team a to be
present in projected team a namespace
that a steamie classes should be present
in project eight or themes B namespace
let's see how to do that so first of all
to create a namespace we use namespace
keyword let's say project a and then
within that I want to create another
namespace name space team a so all the
classes you know that belong to team a
will be present in this namespace let's
say for example I want to have a class
class let's say class a and within this
let's say I have like static be word
print method and then this method let's
say console.writeline
we'll call this team a print method just
to differentiate okay so if you look at
this we have this class class a which is
presented this namespace so the fully
qualified if somebody has to use this
class they have to they have to use this
project a door T made of Class A so in
my main method if I have to use this
print method then I have to use this
project a namespace look at that project
a and this curly braces by the way they
indicate that it's a namespace and
something like this is a class something
with I is an interface so by looking at
the symbols you basically can say what
this curly braces namespace so project a
dot look at that in project alias team a
dot you see the class a and within that
class a I have that print method so I'm
able to call the printer now if I go
ahead and run this program so obviously
it will say team a print method okay so
either can use the fully qualified name
like this or if I don't want to use the
fully qualified name then I can use the
using directive they're using projected
or team a and the moment I do that look
at this it says class a print which is
coming from team a projected a team a
namespace similarly let's go let's make
a copy of this now on this project a I
have another team called team B which is
working and that team b has also
developed a class called class a and
they also have a print that so if you
look at this we have Class A and
projected or team B namespace and we
also have a Class A in project a the
team a namespace now if I have to use
this print method which belongs to team
B how do I do that again there are two
ways one is I can use the fully
qualified name so project a
the moment I say dot now you can see
that there are two names faces team a
and Team B now I want to use team B
sprint method so team B the class a dot
print and by the way we need to modify
this text so that we know this is team V
sprint method so to invoke you know team
a print method we are using the using
directive and we invoke the team B print
method we are using the fully qualified
name for this print method the fully
qualified name is namespace dot class
dot the print method so if we go ahead
and run this both team a and Team B
print method will be called okay now
let's say I also use this directive on
the top instead of using the fully
qualified name let's say I also use
using project a dot team B and the
moment I do that look at what's going to
happen now both of these references are
giving any compilation at a class a is
an ambiguous reference between projected
or team a and project aid or team B's
which to which namespace are you
referring from where should I get this
class a because in both these namespaces
we have the class okay so there is an
ambiguity and if I try to build the
solution the compiler will not allow me
to do that until I resolve this
ambiguity and they're basically two ways
to resolve this ambiguity one is to use
fully qualified names
so and we have already seen that so
project a team a dot class hit of print
and similarly project a team B plus
header prim so now we are able to
compile and call the respective method
so one way to avoid the ambiguity is to
use the fully qualified names and
another way to actually use a piggledy
is to use something called namespace
aliases let's say I don't want to use
this fully qualified name because it's
too long okay what I can do is I can use
a namespace a yes
let's say this is the long one project
aid or teammate or when we use that so
what I can do this project a team a you
can use an alias for that like that
and similarly project a team B this is
an ally as instead of typing this entire
thing we can use PA ta and pa TB so now
I'll actually say I think it's the other
way round
I got the syntax incorrect so PA ta is
equal to that and pa TB is equal to that
okay so now I can say
pa pa dot look at that
that comes from project a flower team a
similarly
peb this comes from project a team b so
we can resolve the ambiguity between
classes you know either by using fully
qualified names are by using alias names
alias directives so this is an ally as
directive for project hitter team a so
how are these alias directives use and
there are two purposes one result
you know ambiguity between names and the
other one in the namespace are you know
names are too long and then we don't
want to use such a lengthy namespace
then we can use this namespace ids okay
now some people say you know using
actually using statement is good okay
but then if they use the using statement
let's look at this project a tour team a
class a let's say for example using you
know if we use the other namespaces as
well okay okay now let's say I am saying
okay class a dot print now where is this
class a coming from how do I know that
you know because I'm not using the fully
qualified name here so I really don't
know where is this class a is coming
from is it coming from system namespace
projected or deem a system dot
collections or system good configuration
unless until I go and hover my mouse
over that class I will not be able to
tell from which namespace has this class
come from okay so some people say using
names faces like this is not a good idea
because the program is less readable you
don't know where is this class coming
from so what they suggest is using a
fully qualified name okay but some
people say using fully qualified names
too much typing ok if you just hover
over the mouse you
come to know what the cloud you know
from which namespace did this class come
from so it's a kind of an argument you
know some people like using fully
qualified name
some people like using the you know
using directive but there are advantages
and disadvantages of both you know if I
use the using directory I know it's the
program is not that readable I have to
hover my mouse to figure it out from
which namespace is this class coming
from on the other hand if I start using
tool equal it by name you know then it's
too much of typing ok so either this or
that instead of that if we use you know
namespace aliases something like this
pata just like how we have done it
before
and then if I say pata dot plus a now I
know that this class a is coming from
pata pata a project a team a so there's
less typing and at the same time the
program is also readable so this is
something in between these two extremes
okay so using namespace
Arya's directives help readability apart
from so I'll wind you know namespace and
do it ambiguity okay so let's go back to
the slide so namespaces why they are use
they used to organize your programs and
they also provide assistance in a wiring
name clashes okay another important
concept that we need to understand is
namespaces don't correspond to file
directory or assembly names wouldn't be
mean by that actually look at this one
you know when I build this project if
you look at this project introduction to
sees c-sharp project in this project we
have you know project 8ot made of Class
A and project 18 B dot plus a and we
also have this program okay so if I
build the solution now what happened is
this entire C sharp code is actually
compiled into an assembly and there is
that assembly present right-click on
that project name
and select open folder in Windows
Explorer and if you go to the bin
directory debug so there you have this
assembly so introduction to c-sharp go
to exe so in this assembly all this code
is compiled and this code is present in
this assembly so do the assembly is one
in this assembly we have projected or
tech team a namespace as well as
projected or team B namespace okay so
okay so so the assembly is this do the
assembly is the same it can contain
different namespaces and different
classes okay now the same application we
can actually rewrite in a different way
instead of having these two you know
classes present in this assembly I can
actually go to the solution add a new
project and we'll go ahead and select
visual C shop class library I'm going to
call this project s project a dot team a
so I'm calling this project it's a it's
a visual C shop is a programming
language the type of project is class
library and I'm naming this project has
projected of team a so this is creating
a project for us called projected or
team a and I'm going to rename this
class as class a so this has created you
know there is a namespace projected or
team A and Class A so what I'm going to
do I'm going to remove this from there
this method from there I'm going to get
rid of this piece of code from here so I
am removing this code from this
introduction to c-sharp
project
instead I'm having this method here
similarly I'm going to add another
project for Team a dot projected of team
B so I'm going to add you'll see shop
class library and this time we're going
to call this project a dot T B and I
click ok so this is going to create
another assembly and I'm going to call
this again Class A and this time you go
ahead and get this method and get rid of
this school as well so you know
introduction to c-sharp project all I
have is a main method okay we don't have
projected a teammate or class a we don't
have project aide or team lead or class
a ok they are in their respective
assemblies so this is team B's print
method so what have we done so far
I've created another project of type
class library and I have created Class A
in this assembly and I've created Class
A for Team B in this assembly protocol
of team B now if I go ahead and build
solution what's going to happen it will
build the respective assemblies as well
so my Class A is no present this is
humbling so let's open this solution in
Windows Explorer so if I open the
solution in Windows Explorer you see
that we have projected or team a and if
I go into the bin directory you see that
projected or team a the DLL and inside
that we have Class A inside that we have
you know the print method and to prove
that in visual studio I mean if you go
to start all programs Microsoft Visual
Studio 2010 and if you go to Microsoft
Windows SDK tools there is a tool called
il
assembler intermediate language
disassembler and now you can actually
say file open and go to your C Drive
introduction to c-sharp project a low
team a into the bin directory and there
is this assembly project a door teammate
or DLL select that and look at this the
namespace is projected or team a within
that we have a class called class a and
within that class a we have a print
method similarly if you go back to that
folder we have project a toad team b bin
method bin folder and you have projected
or team b and it has its own class a and
print method now these classes class a
and this class a are present in their
own assemblies but still what I can do
is this is a different project so now I
want to use this assembly and
disassembly in this project to do that I
can go to the project right-click add
reference and I can add a reference to
this both of these projects so what
happens now project it a team a and
project a door TB both of these these
are referenced in this introduction to
CC shop project and I can start using
them so using project a door team a and
look at this
do they are present in different
assemblies I can still say project a ok
project a is present you know in in this
assembly as well as in this assembly the
same name space team a is specific to
this is MBM Team B is this assembly so
what I mean to show here is that
namespaces do not correspond to a
specific file directory or assembly
names it could be written in separate
files and separate assemblies it still
belong to the same namespace and then
space basically
and be nested in two ways okay one way
is basically to use like names Facebook
project I mean name space project a dot
team a or what you can do is you can say
name space team a so you can nest this
like this as well you can use dot
operator or a curly brace and then name
space again with that or a dot operator
like this so namespaces basically can be
nested in two ways
okay let's complete this so Team B and
obviously will have the same issue again
if I say Class A because that's an
ambiguous name so it's better to either
use a fully qualified name or a
namespace a yes so pata equals that p8t
be project a team B is that so if I want
to use project team is class then I can
say class a dot print and similarly
project a team B that class a printer so
if we go ahead and run this and I both
team a and Team B print method will be
called with some reason unable to copy
that's because I think we have this open
so let's close the disassembler so team
a print method and team b print method
so namespace alias directive sometimes
you may encounter a very long name space
in which to have it shorter which could
improve readability and still avoid name
place name clashes similarly named
methods we have seen this example of a
namespace
and we have seen how to avoid ambiguity
between namespace members if they share
the same names either by using fully
qualified name here in this case or
using namespace alias directives in this
case now until this moment you know in a
namespace we have just seen that we can
have classes but apart from classes we
can have interfaces delegates etc as
well okay so a namespace can contain
another namespace class interview
structure you name delegates etc okay
we'll be talking about classes interface
structures enums and delegates in a
later session so that's it for today
thank you for listening
have a great day