#8.1 Kotlin Object Oriented Class Definition; init Block and Primary Constructor

hi registering Siddarth and welcome to
the next video of this object oriented
programming in Kotlin now in this video
let us check out how do we define a
class in case of Courtland similar to
Java in case of Kotlin we have the class
definition like this class keyword
followed by the class name and this is
the class body and now this class name
customer is actually known as the header
of the class so always remember this now
how do we define the constructor in case
of Kotlin so here is some example class
customer followed by a bracket open and
close inside which we can simply define
some parameters such as name string like
this so this name is actually the string
and it is actually the primary
constructor so this is the way we can
define the primary constructor in case
of Cortlandt now if you notice here this
constructor does not contain any body
unlike in Java where we had the
constructor defined explicitly inside
the class body right now the question
arises how can we initialize all the
field variables in case of Kotlin so for
this we have a init block so init
followed by curly bracket open and close
inside this we can simply initialize all
the properties or the field variables in
case of Kotlin so this is a typical
example of a class containing the
primary constructor and also the init
block let us now proceed and check out
what are the concepts that we will cover
in this video so first of all we will
check out what are properties in case of
Kotlin that are also known as the field
variables in case of Java and then we
will check out the significance of the
primary constructor init block primary
constructor with the property and also
the primary constructor with just
parameters now what is the basic
difference between these two such as
primary constructor with property and
with parameters we will check out in
this video so let's get started so here
inside the IDE here I have my main
method now down the side let us create
our
such as a student right and this is the
class body and I guess in my previous
videos I already taught you how do we
define a class in case of Cortland now
to instantiate this class we can simply
use let's say where space student equal
to student so typically in case of
Cortland we define we instantiate our
class by using where space student equal
to student now notice here we don't have
any new keyword unlike in Java right so
the syntax is more cleaner and more
precise compared to Java and now suppose
student has some name so for that inside
the student class as a part of body we
can simply define some field variables
which in Cortland is known as property
so here I will simply use where name
which is other type of string now here
it will show some error that the where
name must be initialized or should be
declared as abstract so here I will
simply give it a default name as let's
say dummy let's call it a dummy name and
now here I will simply initialize this
property inside the main method by
simply using object name student dot
let's say name equal to shrimp which is
my name pretty cool and now if I want to
print the name inside the main method I
will simply write a print statement
named as let's say dollar interpolation
curly bracket open enclose student dot
name so if I run the code right now I
will get shrink in the output with this
statement right so here I get student
has got a name as shrink so here you can
notice I have simply created the object
of the student class and and defined the
property or the field variable as name
equal to dummy which is the default
value and here I have simply overwritten
the name of the student as shrink and
here as simply printed out the statement
now now suppose if I want to print this
it meant inside that last student so
what do I do
so here I will simply create a init
block right now this init block is
immediately executed after the creation
of the instance of the student class so
when this statement is executed this
init block will be called right after so
inside this I will simply cut this
statement from here and paste it here
right now here if you notice the student
is not defined inside the class student
right because the scope of student is
actually applicable inside the main
method here right so here what I will do
I will simply remove it and now here I
want to print this name string so for
that what I will do is this student dot
name has been defined here now what if I
pass this value as a parameter inside
the constructor like we do in case of
Java so in case of Cortland we have the
concept of primary constructor so let us
say constructor and simply here declare
name colon string right so here I will
simply pass this shrink as a parameter
and now let us remove it and also I
guess I can comment this name from here
right so inside the init block I can
simply print the name as dollar name
which is basically this incoming name
from this constructor right and now here
as per the Cortland coding standard if
you do not specify any modifier such as
add the rate inject or something like
that so here you can simply skip this
constructor keyword and append it to the
header so our code is now looking more
cleaner so this is actually the header
along with the primary constructor
defined here so as soon as this
statement will be executed we will get
student has got a name of shrink in the
output console so let us now run the
code so again in the output we got
student has got a name as shrink right
and now suppose I want to print the name
of the student after
statement that is inside the main method
somewhere here right so for that what I
will do is I will simply use student dot
name but here if you notice this name is
actually undefined but you must be
thinking we have simply specified this
name as a parameter here so why can't we
access it here right inside the main
method this is simply because this name
string is actually just acting as a
parameter this is not the property of
the class student that we had earlier in
this class right so similar to any other
constructor as for example in case of
Java you can simply define name here and
now inside the init method which is
actually the part of the constructor you
can say the primary constructor this
name can be initialized as name equal to
name and now this name is actually this
name so we have to tell the compiler by
using the disk keyword so this name
which is basically this name has been
now initialized to this name incoming
right which is actually strength so
finally this where name is now has now
got the value of shrink so inside the
main method and now we can simply access
student dot name and can simply print
the value pretty simple so if you copy
the statement and suppose paste it here
and now here you can simply print
interpolation student dot name then this
code will simply print the value of
strength from the main method itself and
now just to avoid some confusion let us
rename this name as underscore and here
as well you can rename it to underscore
and here if you want you can also put an
underscore here that will simply refer
to this name variable or you can simply
use dollar name that is actually
pointing to this name property variable
and now as per our current example we
are actually assigning the value to this
name variable in two steps that is we
are simply passing the name shrink which
comes here and
then inside the init block we are simply
assigning the value to this name right
now what if if I simply tell you that
you can simply declare this variable
name property right inside the primary
constructor so what I'm talking about is
you can simply call where space name
right
so here let us comment this and here if
you notice we have simply declared a
property inside the primary constructor
itself so instead of doing it in the two
step we have just done it in the one
step by simply using the ver keyword
inside the primary constructor or if you
want the immutable variables then simply
use Val here like this so the primary
constructor simply supports Val and also
where as well so this can be removed
from here and now our code will now
again work perfectly fine let us run the
code so again we got student has got a
name a string and here let us remove
this comment this will make our code
look more cleaner so this was all about
this video where we learned how to
declare a class the primary constructor
and also we learnt about the init block
and along with this we also learned
about the property of the class and also
we can declare the property right here
inside the class body so this was all
about this video thanks for watching and
have a good day