#9.1 Kotlin Tutorial for Beginners Lambdas and High Level Functions Part

hi registering Siddarth and welcome to
the next video of the scotland
programming series now in this video we
will talk about high-level functions and
lambdas expressions now as a beginner
you might feel the difficulty to
understand these two concepts but I will
try to explain you each and every
concept in detail so I will simply
divided this module in the sub sections
so in this video we will have the brief
introduction of the high-level functions
and lambdas with the help of a small
demo in which we will try to implement a
code with the help of object-oriented
programming way using the interface and
then we will use how to use the
high-level functions and then we will
use the lambdas expressions and in the
next video we will talk about the
lambdas and high-level functions in deep
detail with the help of explanation as
well as demo so this video is all about
the introduction video so what are
high-level functions in Kotlin now in
Cortlandt we have functions that accepts
functions as a parameter so instead of
passing a string or integer we can
simply pass a function as a parameter to
some other function right and then from
a function we can also return a
particular function and also at last we
can have functions that can either
accept the functions as a parameter and
return of function as a value so if a
function can satisfy any of these three
criteria then that function is known as
the high-level functions now next comes
the lambdas now the lambdas in a simple
words can be defined as it is just a
function without any name now trust me
the concept of high-level function and
the lambdas is very very important if
you want to jump into the Android
development with Cortland as a
programming language so make sure you
understand all these concepts of
high-level functions and lambdas in this
4/5 videos that I am going to show you
in this module so make sure you watch
each and every second of this module so
inside the IntelliJ IDE
having a class program inside which I am
having a simple method to add two
numbers that takes a and B as a
parameter find the sum and then print
the sum right and inside the main
function I am simply creating the object
of the program and then calling this
function so if I run this code right now
we get nine in the output console no
doubt in that now now the same program
can be written with the help of an
interface that is when we are going to
print the sum of these two numbers we
are simply going to use the interface so
for that let us define the interface
down the side so here I have simply
defined my interface with a function of
execute that takes a parameter of
integer value let's say sum if you don't
know what is the interface then you can
simply call this interface as a listener
suppose on click of a button something
should happen so what should happen will
be determined with the help of this
interface right like in Android we have
button dot on click listener on touch
listener on double-click listener and so
on all those are actually interface in
android or java right so similarly I
have simply defined the interface having
this method of execute so let us now
proceed forward and let us copy this
method and paste it at the top inside
the class program let me change the
commit line so I am simply going to use
the same method and print the sum with
the help of interface right so here as a
third parameter I will simply call I
will simply define the third parameter
as let's say action and then the name of
the interface as my interface now this
my interface is user defined so you can
change this name as per your wish and
this method is also user-defined right
and now inside this what I will do is
suppose this println is actually the
body let us assume it right so here as
well this println is actually the body
so in place of println what I will do is
I will simply use action dot let's say
execute
and simply pass some as a parameter and
now let us leave this statement as of
now here and now inside the main method
let us try to call this add two numbers
method that has a third parameter as the
interface so what I will do is I will
simply called program dot add two
numbers and I will simply select the
second one that takes three parameters
to let's say seven and the third
parameter will be the interface now if
you are from a Java background then you
must be knowing that you cannot
instantiate or create the object of an
interface you can never do that so how
can we use this interface so for that as
per the Java we need to first create a
class that implements this interface
right and right after that we can simply
implement this method that will be
called when this statement will be
executed so in case of Java or in
Android we used to have new on click
listener something like that and inside
this we actually use to implement the on
click method right but in case of
Cortland since we don't have a new
keyword that creates the new instance
that implements this interface so in
place of this we have the object keyword
so define the object keyword followed by
colon then followed by my interface now
here I will simply define the body of
this my interface and then hit enter now
here it shows some error that we need to
implement the method
so simply press alt' + enter' and
implement the member and then head on
okay so here the IntelliJ IDE has simply
created the execute method for us so
here we have the override notation so
inside this we have to define the method
body now our body in our case is print
Ln sum so simply copy it or cut it from
here and paste it inside this overridden
execute method now if I run the code
right now let's see what happens
so here in the output console we get 9
again so this shows that by using the
object-oriented way that is by using the
interface we have simply got the same
output right now let us come to the
point now even if you have not
understood what I have done here using
the interface then please do not worry
about it
because the main motive of this video is
to understand the lambdas and high-level
functions now at the end let us come to
the point let us use the lambdas and
high level functions and try to get the
sum of these two numbers using the
lambdas right now in order to use a
lambda first we have to define a
function that is the high level function
that can accept a function within a
function so let us define a new function
and then let us change the command line
and now here as a third parameter I
won't use this interface I will simply
use some lambda expression that I will
talk about it shortly and then we will
change the body as well here now here
inside the main method what I will do is
I will simply define a lambda expression
now how to define a lambda is that use
the curly braces open and close and then
you have to define a variable let's say
let's call it s now followed by -
followed by arrow and then the body the
body is actually print line sum so
simply copy it and paste it here and
instead of sum let's call it s now
whatever we have written inside these
two curly bracket are actually the
lambda function or expression so the
lambda expression is nothing but just a
function now why do we call it as a
function now just because this is
actually the function without any name
now suppose here I have add two numbers
this is a function with a name add two
numbers but here this lambda expression
which is actually the function has no
name it has just some code written
inside it now here this s is actually a
parameter
like int a and int B here are the
parameters inside the add two numbers
similarly here this s is actually acting
as a parameter then right after this
operator of arrow you will find print Ln
s now this is actually the body of the
method right similar to what we have
written here this is the body of the
method of active numbers
similarly print Ln s is actually the
body of the lambda expression or
function now here it shows some error
that I will talk about it shortly so but
before that here let us define let's say
Val test of the type of strings equal to
let's say hello so here I simply defined
a variable of test of the type of string
equal to some value of hello right now
similar to this this lambda expression
can also be assigned to some variable
such as test so here what I will do is I
will simply define the Val let's say my
lambda equal to s followed by the method
body this is actually the parameter and
then we have the method body don't
forget it now the compiler wants to know
the type of this s variable so this s is
actually of the type of end now here the
error will be gone now instead of
declaring the SS int we can also define
the type of expression to this variable
of my lambda similar to what we have
done here this is a string hello so we
have simply declared that this hello is
actually of the type of string so this
test will now become string right so
similarly my lambda followed by colon
and then what I will do is the first one
is actually the parameter which is of
the type of int so here bracket open and
close inside this let us use I and T
which is actually the parameter then
followed by - arrow and then this print
Ln s now what is the type of the body
which means that what exactly you are
returning
from this method now since I told you
print LNS is actually the content of the
body of this method so this println
method does not return anything it
returns void or unit so here what I will
do is I will simply write unit right now
suppose as a body if we had let us say 2
plus 3 which actually returns the
integer value 5 so here I will simply
write int fine
similarly if we have here let's say
hello then this body will actually
return the string so here instead of int
I will simply write string right now
here since let us get get back to
originality
we had the print LNS that simply returns
nothing which means unit right so this
completes our statement of lambda now
still if you have any doubt then please
check out my next video where I will
talk about what are the content of a
lambda expression but as of now let us
proceed ahead and now what I will do is
I will simply try to call this function
now remember this my lambda is actually
a function so here if I call let's say
program dot let's say add two numbers
and then simply pass 2 comma 7 now the
third parameter I want to pass this my
lambda so let us call it my lambda since
this my lambda is actually the function
that we are passing to another function
right so that is why this function is
now acting as a high level function with
that simply accepts lambda as a
parameter that is a function as a
parameter so here my lambda will fall
here so here I have to define the name
of the variable for this function let us
call it the same one as action so let's
here called action followed by colon
then give it a space and now here since
a and B are of the type of integer so
this action function should also can't
some type and that type is actually
coming from here integer followed by
unit right command C and command V so
when we pass by lambda which is actually
the function coming from end going into
unit so we can read it as this function
action coming from a end to a unit so
this unit is actually the return type of
this print Ln s whatever value we are
returning from the body right here if
you notice inside this method of actin
numbers we have the body of print Ln
some now this body we have already
defined inside the print Ln s that is
inside the lambda expression so what we
can do here is we can simply comment
this statement and instead of this
statement I will simply call action as a
parameter simply pass some now when the
code will be compiled then this
statement action parameters sum will
actually be replaced by print line s
right so what we are doing here is this
sum will now be substituted by this s
and this S which is going into the body
of print line s so here we are simply
getting the sum print line sum or just
to avoid confusion let us call print
line sum so when the code will be
compiled the action sum will actually be
converted to this print line sum and in
the output we will get the sum of a and
B that is 9 so let us not run the code
and let's see what happens so in the
output 10 so will we again get 9 so this
shows that our code is now working
perfectly fine again
with the help of high level function
with lambda as a parameter now we can
simply remove this code from here so
here in front of you I have simply shown
you a very simple way and then using the
interface or the object-oriented way and
then finally the comparison of these two
methods with the high level functions
with lambda as parameter now at the end
I will simply conclude
video by simply telling you dad we can
directly put this lambda expression
control X or control C in place of this
my lambda variable so when this
statement will be executed we are simply
passing the lambda expression directly
but earlier we were using the my lambda
variable so the code will execute fine
now again at last you must be thinking
if we were able to achieve the same
thing with the help of this simple
method and by using the interface as
well then why do we need to have this
lambda expression and high-level
functions but trust me then you will
enter into the Android application
development you will be surrounded by
lambda expressions and high level
functions all around so for that you
have to simply clear your concept about
these two concepts right here only and
in case you have not understood the
lambda expression and high level
function in this video then please check
out my next video where I will talk
about these two concepts in deep detail
this is shrinkage are signing off and
thanks for watching
have a good day thank you