#8.2 Kotlin Android Tutorial: Secondary Constructors Video Lecture | Kotlin Tutorial for Beginners: Learn Kotlin in easy language - Back-End Programming

hi this is strength of the heart once
again welcome to the next video of this
object oriented programming in case of
portland now in the previous video we
learnt about the properties primary
constructors init block and so on now in
this video let us now check out the
concept of secondary constructors in
case of Cortland so unlike Java in case
of Cortland we have the concept of
secondary constructors as well so here
what I will do is inside the same
application that we created in the
previous video inside the class of
student what I will do is I will simply
declare a secondary constructor now to
declare a secondary constructor you have
to simply use the keyword of constructor
followed by simply define the parameters
now if you are declaring the secondary
constructor then make sure you give an
explicit call to this primary
constructor as well because the compiler
won't allow to write such code without
calling this primary constructor from
this secondary constructor now what I
mean is you have to simply declare such
as named string and then let us use the
parameter of ID let us say int now
followed by colon followed by simply
give a call to this primary constructor
by simply passing the name right and now
unlike the primary constructor this
secondary constructor has its own body
so the primary constructor does not
contain its own body but you can create
this init block as a part of this
primary constructor that we saw in the
previous video so the secondary
constructor has its own body and here
you have to simply call this primary
constructor because without calling this
primary constructor let's see what
happens it simply shows some error the
primary constructor call is actually
expected so with the help of this
keyword you can simply call this primary
constructor that will simply instantiate
this field variable of name now it is
not mandatory to keep this name and this
name as same you can also call it let us
say n so here
simply give a call to end right now
currently if you notice this ID is just
acting as a parameter inside the
secondary constructor unlike this name
which is actually the part of the class
and behaving as a property of the class
but this ID is not the property of the
class so for that let us append vert
keyword and let's see what happens
so the IntelliJ ID is showing that we're
on the secondary constructor is not
allowed as a parameter so in Cortland
you cannot declare the properties inside
the secondary constructor
unlike the primary constructor where we
have declared name as a property of the
class so this vert Orwell is not allowed
inside the secondary constructor so what
is the solution for this so for this we
have to simply declare where ID equal to
let's say minus 1 this is the default
value assigned to this ID now let us
declare the type of the data type let's
the int right so now we have simply
defined the property of the student as
their ID in equal to minus 1 which is
again the default value so inside the
body of the secondary constructor we can
simply use this keyword this dot ID
equal to the incoming ID and now you
cannot access this ID inside the init
block and now inside the main method you
can simply use student object dot I ID
and simply print the ID of the student
let us use the print keyword and let us
now also pass this comma 10 now
previously when the statement was
getting executed it was simply going to
call this primary constructor but
suppose if you have got the value of the
student ID then in that case simply call
the secondary constructor by simply
passing two parameters let's say the ID
of the student is now 10 so when the
statement will be executed it will
simply call this secondary constructor
where n will get the value of student
and this ID will now bitten and
explicitly we are calling the primary
constructor that simply passed the value
of strength that will be now
toward inside the where name right and
then we will print the statement as
student has got a name as shrink and
inside the secondary constructor we are
simply initializing property of ID as ID
and now here I am simply printing the
student ID let us now run the code and
now in the output console you can see
student has got the name as Sri egg and
this is the ID of the student now you
must be thinking why did not I print the
student ID inside the println statement
within the init method let us try this
out as well let us say an ID is dollar
ID right let us now run the code again
and now this time I have simply got this
output student has got the name as Sri
egg and the ID is minus 1 and right
after this statement when this statement
is executed we are getting the perfect
IDs 10 now why this ID is being printed
as minus 1 which is actually the default
value of the ID now what happens is that
when this statement is executed student
shrink 10 so what happens is that it's
simply called this secondary constructor
now this secondary constructor simply
call this primary constructor which in
turn simply execute this statement init
block now right after the init block is
executed this statement is executed
right so when this ID has got the value
of 10 but before that this statement was
already executed where the ID was minus
1 so here you can simply write a comment
line the body of the secondary
constructor is called
after the init block so that is why the
value of the ID is minus 1 instead of 10
so always remember this so at the end of
this video let us summarize in this
video we learned about the secondary
constructor and also we cannot declare
the property like where space ID inside
the secondary constructor and if you are
declaring the secondary constructor then
you must give a
- the primary constructor like we have
done here and this will simply call this
constructor present here which is
actually the primary constructor fine so
here let us remove the school from here
which is of no use so this was all about
this video thanks for watching and have
a good day