Part 26 - C# Tutorial - Why Properties.avi Video Lecture - C sharp Enhance

welcome to prism technologies I am
venket this is part 26 properties in
this session we will learn the needful
properties consider the example that you
can see on this slide we have a student
class with three public properties now
marking the class fields public and
exposing them to the external world is
bad because you will not have control on
what gets assigned to these properties
and what gets returned back from them
okay for example on the right hand side
you can see the problems with public
fields you know specific to this example
for example the business rule states
that student ID should be a non negative
number
nobody should be able to assign a
negative number but since this is a
public field I am able to do that so
it's violating the business rule
similarly for example the student name
cannot be now but this example you know
is setting that to mal again why is that
happening
because you exposed your class fields
public okay so let's look this in action
so I have the student class with ID name
passed mark all of them public
properties ah sorry feels now let's go
ahead and create an instance of this
class student let's say c1 is equal to
new student and now our business rule
states that the student ID shouldn't be
set to negative number but here even if
I set to a negative number it is happily
accepted similarly name should not be
not now but here I am able to do that
without any issues and similarly for
example nobody should be able to change
past mark because it is set to 35
somebody should be able to only read
this feel that they shouldn't be able to
change this value but I can go ahead and
change past mark to zero so anybody who
gets 0 would also get past okay and
let's go ahead and print this for
example console.writeline what I want to
do is I want to print maybe ID is equal
to whatever is the ID
and maybe name is equal to whatever is
the name
and similarly passmark
is equal to whatever is the past mark so
let's substitute the values for that so
ID is in C 1 dot ID property and
similarly name is in C 1 dot name and
past mark is C 1 dot last mark
so now if we go ahead and run this
program in a look at this
um ID shouldn't be non-negative but I am
able to set it to negative negative and
I'm able to print that and name
I shouldn't allow an empty name to a
student but since these are public fills
I'm able to do that and another thing if
you go back to the slide if the student
name is missing then no name should be
returned instead of an empty string look
at this here name is set to null which
means nothing so if there's nothing in
the name I should get in the output when
I try to print it no name instead of an
empty and I'm string and similarly path
mark somebody you know nobody should be
able to change that say read-only field
I want to make it a read-only feel but
since it's a public field people are
able to change it in our - maybe - 100
or 0 in our example and then that 0 gets
printed out so all violations of the
business rules are happening so if you
want to enforce these then probably you
want to turn your fears your public
fears into private and have some sort of
mechanism in place to control what gets
into these fields and what gets out of
these fields ok so let's see how to do
that actually you know in the
programming languages that doesn't have
properties they use getter and setter
methods this has been there from you
know since the inception of
object-oriented programming and remember
that you know we have seen inheritance
polymorphism which are which are you
know two of the four pillars of
object-oriented programming and
you know encapsulation is yet another
pillar of object-oriented programming so
how do you achieve encapsulation
basically achieve encapsulation you know
in programming languages that doesn't
support properties using getter and
setter methods but very as in c-sharp
you know in.net programming language in
C sharp and vb.net
we can make use of properties okay which
we'll be looking at in a later session
but for now let's see how we used to do
it before properties we used to have
getter and setter methods for example
let's say I don't want somebody to be
setting the ID to be negative so how do
I do that first of all you have to mark
all these fields as private because we
don't want want to be exposing our
fields directly to the external world so
let's convert them to private and let's
do the same thing with the rest of the
fields so private and private and then
since this is a private field I want to
follow a good naming convention as well
so I'm going to use an underscore
similarly under school name and
underscore pass mark okay now since this
is a private field nobody will be able
to access that outside of that class
which we will be talking about X
modifiers in a later session okay now
but then somebody should be able to set
the ID value and they should be able to
read the ID value and to do that we
actually provide a method so a public
method basically to set a public void
let's say we call it set ID and
obviously they should pass an ID into
this method as a parameter so we can
assign this parameter to this field but
then before assigning we can inspect the
value that is coming into this class so
if
that ID parameter is less than or equal
to zero then we know that it's n on a
lab value so what you can basically do
is to an exception again we haven't seen
exceptions yet we will be looking at
them in a later session but exception is
nothing but an error condition we threw
back an error to the user saying that
you know any number less than zero is
not allowed okay so through new maybe
exception and we'll give a meaningful
exception like student ID cannot be
negative okay otherwise if it's
non-negative if it is greater than zero
then probably we will set you know this
class ID field to the ID that's getting
past ten and so this just sets the value
but if they want to read that ID value
then we need to have a get method so how
do we do that public and since we have
to return the value back so it needs to
be an end and get ID so what will this
do this will simply return the ID value
this dot ID so now we know that if
anybody sets a value to this field it
has to be set only using this method and
similarly if anybody has to read this
field they have to do that using this
method so now we have control on what
gets into this field and what gets out
of this fear okay so in this case let's
say for example we have only implemented
the ID we'll do we'll do it for the
other fields in just a minute but before
that let's see how to initialize that so
I have the student object which is c1
and if I want to set the ID now look at
this when I press dot I don't see any of
the fields there I only see the set ID
and get ID method so if I want to set
the student ID I can say set ID and if I
pass let's say minus one zero
let's go ahead and see what's going to
happen let me dam let's comment this
line
oops just these two lines let's call
them and run this now we said that we
shouldn't be able to set a negative
number but here we are setting the
negative number so what's going to
happen
set ID is getting is going to get calls
if you right-click on that set ID and
say go to definition which is nothing
but this method so as ID
what are we passing - 1 0 1 so 1 0 1
gets passed is - 1 0 1 less than or
equal to 0 this condition becomes true
and it rules an error saying student ID
cannot be negative okay so we have
control so let's see if we get that
exception so if we go ahead and run that
and somebody is trying to set that to a
negative number so you see that there is
an unhandled exception student ID cannot
be negative so now the user is lettered
whoever is making use of a class they
know that they cannot set a student ID
to negative number so on the other hand
if I set to a positive number I go ahead
and run that I don't get any exception
but on the other hand if I have to go
ahead and print that let's see how to do
that to get the value console.writeline
let's say student ID is equal to
whatever so how do we get the student ID
that is the student object we have a cat
ID method so what is this cat ID method
going to do it is simply going to return
the value that is stored in this private
field ok so now if we go ahead and run
this it returns student IDs 1 0 1 so
these getter and setter methods you know
are protecting this feel now ok
similarly we can make use of you know
other getter and setter methods for the
name so let's see how to do that say for
example I want to set the name so public
wide-set name and obviously if we have
to set the name we have to pass in that
name into this method so if ok now this
name should not be now and it should not
be empty okay so somebody shouldn't be
able to set my name is empty so I need
to check that how do I do that
on the string class there is a method
called is null or empty okay so this
method will tell whether if it is null
are empty if the past and name is null
or empty then what do we want to do we
want to throw an error so throw a new
exception stating name cannot be null or
empty otherwise if it has got something
then we want to set the name field of
this class is equal to the name that we
pass in okay similarly if we want to
return the name back then we want to
have a method get name so the return
type should be string so public string
get name now we need to do a check here
if the name is an empty one if it is
null or empty I want to return no name
instead of an empty string so what do we
do if string dot is null are empty and
which is that one this dot underscore
name then we want to return no name else
what we want to do we want to return the
field itself
this dot underscore name I hope this
makes sense okay because if you look at
our requirement if we go back to the
slide we said that if you go back to the
previous side if student name is missing
if the object doesn't have the student
name and if somebody is trying to get
the value of that field then we should
show no name instead of an empty string
so if somebody is getting the value of
this underscore name field they use this
method and if that field is null or
empty you want to return no name
otherwise if it is not null or empty it
means something is there in that field
we will be we should return that in that
case okay and again actually you know
you can use a ternary operator instead
of this big if else we have seen that in
operators you know video session so
instead of saying you know if and the
else you can basically use this ternary
operator so return what do we want to
return F strength dot is null or empty
then I want to return no name else this
dot unschool name so instead of all
these lines we can basically use the
term operator so if you're not sure how
to enter the operator works please check
my video on operators in this series
okay so let's go ahead and test that so
if somebody is able to set the name -
let's say set name and they're passing
in now
okay so let's see what's going to happen
now I go ahead and run this look at this
unhandled exception name cannot be null
or empty so they have to pass in name on
the other hand let's say they don't set
the name at all
but they are trying to print the name so
in that case what should happen
it should since the name field doesn't
have anything in that it should actually
print no name so get the name of the
instrument so if I go ahead and run this
so student name is equal to no name why
because we haven't initialized the
student name to anything yet but on the
other hand if we set the student name to
something so set name to maybe mark and
now if I go ahead and print this the
student name should be mark so now we
are we have complete control on what
gets into these fields and what gets
returned from these fields similarly I
want to make this path mark field as
read-only field nobody should be able to
change the value if somebody wants to
know what's the plasma they should only
be able to get that that's why I
initialize that to 35 and I only will
have now public int get passed mark so
what is this method going to do it is it
will simply return the value so return
this dot under school pass mark okay so
now nobody will be able to change that
value but if somebody wants to know
what's the pasta they they will be able
to do that using that get pass math
method but look at this there is no set
mark that's why they will not be able to
change that so in our class we made this
pass mark field read-only by not having
a get method
okay so obviously if I want to print a
pass marker student Pathmark
then I simply see one dot get past mark
and we can go ahead and run that so we
get the pass markets 35 so I hope this
is clear in a wanting to keep in mind
never ever expose your class fields in a
public publicly that's bad because we
will not have any control over what gets
into these fields and what goes out to
the external world from these fields so
if you want to have a better control and
if you want to encapsulate those fields
then we make use of properties in
c-sharp in programming languages that
doesn't support properties we use this
getter and setter methods so programming
languages that does not have properties
use getter and setter methods to
encapsulate and protect fields so in
this example we use the set ID for
example to set the ID field and get ID
to return the field 10 capsulate ID
field ID class field as a result we have
better control on what gets assigned and
returned from the others variety fear
and we know encapsulation is one of the
you know four pillars of object-oriented
programming in the next session we will
actually see how c-sharp make use of
properties in order to achieve this
encapsulation without having to use the
getter and setter methods all right so
on the slide you can see some resources
for asp.net and C sharp interview
questions so that's it for today thank
you for listening have a great day