#8.8 Kotlin Tutorial: Abstract class; Method and Abstract Properties Video Lecture | Kotlin Tutorial for Beginners: Learn Kotlin in easy language - Back-End Programming

hi Lisa strings in hearts once again
welcome to the next video of this
object-oriented programming now in this
video we will talk about what are a
straight classes methods and also
properties in case of Cortland so the
classes in case of Cortland can also be
abstract in nature now what do we
exactly mean by abstract we will check
it out shortly now the classes in case
of Cortland can be abstract in nature
now before going for what is abstraction
in case of Cortland first let me show
you what are abstract classes methods
and properties inside the IntelliJ IDE
straightaway and thereafter we will
discuss all the properties of these
classes and methods so here inside the
intelligent I have a class of person and
class Indian now suppose I want to
inherit all the properties of this class
person so I will simply make this class
person as open as simple as that this is
the basic rule of the inheritance in
case of Kotlin now this function becomes
a part of this Indian class right so
this function go to school is actually
is just a normal function with by
default public and final modifier
attached to it so as we all know the
functions are by default public and
final in nature so here is the comment
line for this and now suppose inside the
class of person I define one more
function such as function get the height
of the person now this function is
exactly same as this function both are
public and final in nature by default
now if I want to override this function
of get height inside the class of Indian
such as let's say override function get
height then the compiler will not be
happy because we have to make this
function as open because by default it
is final in nature so after we make it
open we can now easily override the
methods inside the subclass or the
derived class
now here this Indian is actually the
subclass or the derived class as we all
know from the previous videos of concept
of inheritance
now notice here these methods are
actually having the blank body like this
it is totally blank so that is where the
curly brackets are open and closed like
this here as well it is blank right so
this was about the open method and this
was about this was about the final
method right and now let us experiment
more and let us define one more function
of let's say function eat now this time
again define a blank body so this
function eat is similar to this function
go to school which is again final and
public by default right now suppose if I
append here let's say open so this
function it can now be overridden inside
the class of Indian let's say override
function eat simply override this method
and you can define your own custom code
inside this method right here and now
suppose if I change this open to let's
say abstract so what will happen now by
default all the abstract methods are
actually open in nature so you don't
have to specify the open keyword
explicitly so let us remove it so this
is the abstract method now when we
declare any abstract methods or a class
or a property then that abstract
declaration don't contains a body so
here this eat method is actually having
a blank body this is the blank this is
the body of the method right so when we
declare something as abstract then that
declaration should not contain any body
so these curly brackets should not exist
so let us delete it so right now here is
the difference between a normal function
or open function and an abstract
function so here in case of abstract we
don't have any method body and again it
is showing some error this abstract
method is actually present inside the
non-abstract class of person so we will
deal with it shortly so right now
this method is actually abstract in
nature so let us define it so the
abstract properties are actually by
default open by nature right so it is by
default we are having the open keyword
so we don't have to specify the open
keyword again here like this it is
redundant now before rectifying this
error here inside the main method
suppose if I create the instance of the
class of person equal to let's say new
person like this so here it does not
show any error now in order to rectify
this error suppose this method can only
exist within the abstract class so here
I will simply append the abstract
keyword right and now here again by
default the abstract properties classes
and methods are actually by default open
in nature so we don't have to specify
open again because it is by default open
by nature right now here it shows some
error cannot create an instance of an
abstract classes now it is a property of
an abstract class that you cannot
instantiate or create the objects of
this abstract class right so the
compiler will simply throw some
exception here because this is not
allowed to create any object of the
abstract class so here I have to remove
that statement in order to rectify the
error right now what is the advantage of
using the abstract method such as Eid
now here inside the subclass of Indian I
have simply overridden this eat method
and also get height method this gate
height method is actually open in nature
and this eat method is actually abstract
as well as open in nature that is why we
were able to override it here now
suppose if I delete this gate method
from here then the compiler is still
happy it does not show any error because
this open function gets height is
optional we can or we cannot override it
inside the Indian class it is totally up
to our choice but if we remove this
abstract method of eat let us remove it
then here the compiler is not happy it
simply says that this Indian class
should override all the
abstract methods and properties present
inside the superclass of person which is
again abstract in nature right so if you
define any abstract keyword in the
superclass of person so you need to
override this method inside the class of
Indian which is the subclass
so here if you rectify this error I will
simply press alt' + enter' and simply
implement the members and simply select
this heat method and here we go
the IntelliJ IDE as has simply done the
job for us here we have override
function eat and here this is a to-do
implementation and now if you want you
can optionally override this get method
because it is only open not abstract and
now what about the field variables
suppose if I create here where let's say
name of the type of string right equal
to let's say dummy underscore name this
is my domain name right now suppose if I
want to override this property inside
the class of Indian so I have to make
this variable as open as we all are
aware of this similar to what we have
done here right or here by default so
here inside the class of Indian I will
simply override the variable of name of
the type of string and here let's say I
will call dummy underscore Indian name
right something like that so I have
simply overrated the value of name
inside the subclass and now the default
value is dummy Indian name now suppose
if I append abstract here and so we need
to remove this open keyword because it
is redundant right so here now it shows
some error that the abstract variable or
the property cannot be instantiated now
similar to method like we don't have a
method body in case of abstract method
here again we can never instantiate a
property that is abstract in nature so
here we have to remove this equal to
operator so the abstract property and
abstract method are just defined they do
not contain any code inside it right so
now suppose if I comment this here so
the compiler is again not happy because
in the superclass of person we have a
abstract variable name so whatever we
define as an abstract we need to
override it compulsorily inside the
subclass so here if I remove this and
now if I press alt enter so here it
simply shows implement members so simply
click on it select the name hit on OK so
by default the IntelliJ IDE has simply
overwritten the variable name which is
of the type of string now this is the
default getter and setter so let us
remove it we don't need it and now here
if you override a variable or the
property then you need to define its
body that is you need to initialize it
let's say again dummy in your name so
this was all about the abstract plus
person abstract property and also
abstract method and now here let me add
some comment line you cannot create the
instance of the abstract class for your
better understanding so at last let us
check out the properties of the abstract
class methods and also property right so
here the role of abstract class is to
just provide the set of methods and
properties that is the abstract class is
just off the placeholder use it just
provides the set of methods and
properties without any value or without
any method body so the abstract class
are actually partially defined class it
is the class but it is partially defined
right it does not contain its its own
code and next we have abstract methods
which have no body when declared right
and also we have abstract properties
that cannot be initialized when declare
so previously we had this abstract
method that contains no body again we
have abstract property that contains no
value right so at the end what we
conclude from this video
so at the end we conclude that we cannot
create the instance or the objects of
the abstract class right and we always
need to override the abstract methods
properties inside the derived class or
the subclass otherwise the compiler will
show some error this is the basic rule
of abstraction in case of Cortland so
this was all about this video hope you
like what you saw and see you guys in
the next video thanks for watching have
a good day