Part 22 - C# Tutorial - Method hiding in c#.avi Video Lecture - C sharp

hello welcome to prism technologies I am
venket this is part 22 method hiding in
c-sharp in this session we will learn
method hiding and invoking hidden base
class members let's look at an example
in the previous session we have actually
created an employee based class and we
have created to change classes part-time
employee and full-time employee
inheriting from the employee based class
okay so if you haven't watched my
previous session on inheritance I would
strongly encourage you to do so before
watching this video session alright so I
have an employee class the base class
where we have first name last name and
print a full name method within the base
class let's go ahead and create a
part-time employee class which inherits
from they employee class so part-time
employee inheriting from employee class
and similarly let's go ahead and create
a full-time employee class which also
inherits from employee class okay now if
I have to go ahead and create a
part-time employee object or a full-time
employee object I can do so F full-time
employee FPE equals new full-time
employee and from inheritance we know
that if a class derives from a base
class all the all the code that's
present the base class is also available
to the child class so that concept
enables us to initialize this full-time
employee objects first name and last
name
so first name equals let's say full-time
and FTE dot last name equals maybe
employee and let's say I want to print
this employees full name we can call the
print full name method okay similarly if
I have to go ahead and create a
part-time employee I can do so
but I have to use the part-time employee
object so part-time employee is equal to
new part-time employee we need to change
the reference variable named part-time
employee PDE is equal to new part-time
employee and we can say part-time
employee at first name equals our time
and part-time employee last name equals
employee and part-time employee dot rent
full-length now if we go ahead and run
this as you might expect what's going to
happen it will print the full-time
employee and part-time employee names
okay so which is expected but now let's
say my manager told me all right if
full-time employee named printing is
fine but by looking at the name I should
be able to tell whether it is a
part-time employee or a full-time
employee so if if it is a part-time
employee then I want a - contractor
appended to his name so that just by
looking the list of employee names I can
figure out with a full-time employee and
with a part-time employee okay
so to do that what we can do is okay in
my full-time in my part-time employee I
can go ahead and provide it full name
print full name function but look at
this when we do that this part-time
employee class is actually inheriting
from employee based class which has
already got a method called print' full
name in my derived class also I'm having
printful name method now if I do that
what happens this method will actually
hide this method okay so when I say
part-time employee dot print full name
what happens is it invokes this method
and not the parent class method okay so
what did we say we wanted in the output
you know - contractor word appended to
the end of the name so we can say
contractor fine now with this change if
we go ahead and run this what's going to
happen for
part-time employee - contractor we get
that as expected
now look back the code look at this
there is a green squiggly underneath
that print full name function what does
that indicate that indicates that and if
you look at the warning message there
the green squiggly actually indicates
warning so what is this warning about it
is saying that in the part-time employee
class the printable name is hiding the
inherited printful name this method from
this employee we have inherited that but
since this method is here it is hiding
that okay so use the new keyword if
hiding resented intended okay if you
intended to hide this method then use a
new keyword okay so it's just alerting
the developer alright we already have it
print the name of the base class okay
and you have a print full name in the
derived class as well which will
effectively hide the base class method
if you're hiding is intentional then use
the new keyword okay so we can go ahead
and use the new keyword so the moment we
do that and then if I go ahead and run
this once again so what's going to
happen the output is the same except
that we don't get that warning anymore
okay so basically if you want to hide a
base class member then you use the new
keyword okay that's perfect okay now
let's say okay I have hidden the base
class member so anytime I say tailed
class object dot that method it only
calls the child classes method but let's
say I want to for some reason call the
base class method okay in spite of me
hiding the base class method I want to
be in a position to call the base class
method how do I do that
there are several ways to do that one
simple way of doing that is actually to
use the base keyword so in my chain the
class instead of doing this if you want
to call your base class method what you
can do is you can use the base keyword
dot print full name and the moment you
do that
bass refers to the employee class look
at the standard listen choose that and
when I say print full name so look at
the intelligence it says employed
plentiful RAM so you can use the base
keyword to call the hidden base classmen
but that's one way so if I go ahead and
run this now you should look at the
output that I'm employee without that -
contractor proving that we are using the
base class print full name method okay
so that's one way what's the other way
the other way is actually to typecast if
you remember in part 3 I think we spoke
about you know datatype conversions and
we use the typecast operator similarly
what we can do is we can use the
typecast operator and convert this
part-time employee object to be of type
parent and remember you know inheritance
concept in the inheritance chapter that
we have discussed you know a change
classes specialization of its base class
okay so which means a child class has
got all the capabilities of the base
class plus you know whatever is special
to that trail class it's just like a
gynecologist you know a gynecology is a
specialization whereas general surgeon
is you know a a general surgeon so a
gynecologist can do the you know roles
and responsibilities of a general
surgeon plus clinic okay
so similarly a part-time employee can
fulfill all the responsibilities of the
employee class okay
so that fact allows us to perform a cast
on this object so that it can behave as
a parent class okay so how do I do that
instead of saying directly
Pte dot print full name what I can do is
alright I have this parent part-time
employee object what I want to do now is
use the typecast operator and can with
that to be of type employee and on this
converted object I want to go ahead and
call the print full name method now if
you look at the intellisense here print
full name it's saying employee dot print
full names were employee base class
employee classes print full name method
will be called so if I go ahead and run
this now we should get part-time
employee without that -
contractor proving again that the base
class hidden method is called okay so
this is one way and another way which is
essentially similar to the same thing
but doing it with the difference in tax
is that you know I can say okay so
instead of this we can say PT e dot
print for Lam now you know that if we do
this and run this program what's going
to happen it's going to bring up the you
know child class printful lam method but
we wanted to call the base class print
flame method and to do that instead of
using it change the class a reference
variable I can use the parent class
reference variable now remember the fact
that a child class object can fulfill
all the responsibilities of a parent
parent class so that fact again allows
us to assign an object okay an object of
child type to a reference variable of
type parent okay now look at this this
PDE is actually an object of type
employee and employee object or
principal name they'll call the parent
class printful name method so if I go
ahead and run that
look at that part-time employee without
that - contractor again proving that the
hidden base class member is called okay
but if you might be thinking okay can I
do this part-time employee but I'm
employee Pte is equal to new employee
you can't do this this will give you a
compiler warning because an employee
object cannot fulfill all the
responsibilities of a of a part-time
employee so this is not possible but YC
versa is possible it change the class
you know a parent class reference
variable can point to a child class
object whereas a child class reference
variable cannot point it where a class
object okay so keep that in mind because
this forms the foundation for
understanding the next concept which is
polymorphism parent class reference
variables can actually point
objects in that chapter we will also
discuss you know the primary difference
between object reference variables and
objects themselves okay but I may have
in this session we have seen that you
know if you want to hide a base class
member we use the new keyword if you
don't use the new keyword okay the base
class member gets hidden but you will
get a compiler warning this is just to
alert the developer okay if you I mean
there is a base class member hiding
happening if you're hiding is
intentional then go ahead and use the
new keyword okay and we have seen that
there are different ways to invoke a
hidden base class member from the
derived class one is to simply use the
base keyword the other one is to use the
cast on the chain type to be your parent
type and then invoking the hidden member
and the other way is actually making the
parent class reference variable point to
a derived class object and then saying
parent class object dot that hidden
member which again calls the base
classes hidden method on the slide you
can see additional resources for a speed
other than C sharp interview questions
that's it for today thank you for
listening have a great day