#8.10 Kotlin Object Oriented Programming: DATA CLASSES Video Lecture | Kotlin Tutorial for Beginners: Learn Kotlin in easy language - Back-End Programming

let us now proceed and check out one
more concept in case of cotton such as
data classes and also in the previous
video we learned that by default every
class has a superclass of any and this
class of any provides the functions or
methods such as equals method hashcode
method and also to string method so all
these methods are by default present in
every class that we define inside the
Cortlandt file and now proceeding
forward when we use the data classes the
cortland simply provides a copy method
for us that we will check out inside the
demo video and now the data classes
simply provides these mentioned methods
implementation so we can make effective
use of these methods inside the data
classes now what does this data classes
stands for let's check it out so here
inside the IntelliJ IDE I have a class
of user now as a field variable or the
property of the user I will simply
define the name and ID so here I have
simply defined the property name and
also ID of the student or the user right
and now inside the main function I will
simply define two objects of user so
here I have user 1 and user 2 if you
notice here I have user name as Sam and
here Sam as well
IDs 10 and 10 here as well so both these
user 1 and user 2 has the same name and
same ID now if I compare let's say user
1 equal to equal to user 2 then simply
print out equal is not equal so let us
now run the code so in the output we
have not equal now you must be wondering
that these two values are same Sam 10
Sam 10 so why not user 1 and user 2 are
equal just because here we are simply
creating two objects and these are
actually two references so these are two
different objects created inside the
heap memory so here we are actually
comparing the object reference so both
are in this case are different right so
that is why we get not equal in case of
Kotlin now in case of Java as well
if you are from a Java background then
you must be knowing what I am talking
about when we create user and user it
simply creates two different objects but
with the same value and now if I change
this class with the help of a keyword of
data let's say data space class user and
now let us run the code and now in the
output console we have equal in the
output now this is simply because the
purpose of the data class is just to
deal with data not the objects so here
when we compare user 1 and user 2 it
simply compares the values such as Sam
10 Sam 10 so it simply prints out equal
in the output console so this is the
beauty of using data classes when you
want to only deal with the data or you
want to compare the data then simply use
the data keyword in case of class right
and now suppose if I print here let's
say print line user 1.2 string right
like this or even if you don't use to
string then also let's see what happens
now here let us first remove the data
keyword let us now run the code so in
the output we have some address of the
object of user comm dot my Cortland dot
user some address location of this user
one object right now if I use the data
keyword here and now let us run the code
so this time this print line user one is
simply printing out the value of this
user that is named equal to Sam and ID
equal to ten so here implicitly we are
actually calling the to string method
let us run the code again so here we go
the same output is actually present here
so by default this data class actually
provides the default implementation of
the to string method which is actually
the part of the any class which is the
superclass of any classes in case of
Cortland right so that is why we are
getting the value and now proceeding
forward here down the side let me show
you the copy method so
let's say new user equal to user 1 dot
copy method now here I can simply use
new user equal to user 1 dot copy and
let us print it and let us now run the
code so in the output we have the value
of the new user again name equal to Sam
and ID equal to 10 so we are perfectly
able to copy from the data from one user
and then putting it inside the new
reference of new user right and now
suppose I want to override such as the
value of Sam let's say to Peter so I
will simply use name equal to let's say
Peter and now let us run the code so in
the output we have the name as Peter but
the ID is still remaining same that is
10 so in this way you can simply change
value of the variables such as name
while copying the user object to another
right and now suppose if you want you
can also use let's say ID equal to 25
something like that right so you can
simply change the values and if you want
to change the sequence then you can
simply change it by simply using ID
equal to let's say 25 let us now run the
code so here this time the ID will be
changed but the name will remain Sam
like this the name is Sam but the ID is
now changed to 25 now notice here that
we are using the named parameters now
the concept of named parameters we
already saw in the previous module when
we talked about functions in case of
Cortland so we are simply defining the
name of the parameter as ID equal to the
value so no matter what is the sequence
if you define the name parameter then
this value will only fall here in spite
of the first parameter remains the name
and here the first parameter is ID so
the ID will simply match with this ID
and this ID value will now be overridden
from 10 to 25 like this right
and now at the end of this video let me
show you something else
let us now remove this vert keyword so
here it shows some error that in case of
data classes that primary constructor
should only contain
the property parameters such as either
where or either well it cannot contain
the parameter right so always remember
in case of data classes the primary
constructor should only contain the
property variables such as where or Val
so this was all about this video of data
classes so thanks for watching and have
a good day