#7.7 Kotlin Android Tutorial: EXTENSION FUNCTIONS with demo Video Lecture | Kotlin Tutorial for Beginners: Learn Kotlin in easy language - Back-End Programming

hi this is James at the hearth and
welcome to the next video of this module
of functions in this video we will talk
about what are extension function in
case of Kotlin now the purpose of
extension function is to add a new
function to the existing class so it
simply adds a particular function to a
predefined class without declaring it
inside the class and the new functions
actually behaves just like the static
functions in case of Java now
practically also during the compilation
the Cortland compiler also converts
these functions into the static
functions internally that happens behind
the curtain so we do not see what
happens behind the curtain but exactly
this happens so let us now check out the
extension function inside the IntelliJ
IDE so first I will simply create a
class off let's say student inside this
I will simply defined a function so here
I have a method of has first so if the
student has passed the exam or not will
be determined inside this method so if
the mass is greater than 40 then return
true else return false because the
student has failed now let us simplify
this code by simply removing the
redundant code so here I am simply
returning if the mark is greater than 40
then return true is returned false right
now inside the main method I will simply
define a code so here I have simply
written the code by simply defining the
object of the student class and then
Here I am simply passing the marks of
the student as 57 so if the student has
passed the exam or not will be
determined with the help of this code
right now suppose this is our now this
class is actually our own class right so
we are the sole owner of this class of
student now suppose this class is
already defined and later on in your
application you need one more function
inside the class of student so so
without defining the function right
inside the class what you can do is you
can simply create a one more function
let's say function has got scholarship
or not or
scholar so if the student has secured
the marks greater than 95 then he is
actually the scholar as he is not so
this function should be the part of
class student but for that we have to
define this method inside this class of
student but we don't want to do it so
what I will do is I will simply use the
concept of extension function where the
syntax is let's say you need to use the
class name of student command C and
paste it here followed by the dot
operator so here what I have done is I
have simply used student dot is scholar
so whenever I use this syntax this
function is scholar will will now behave
like a function present inside the class
of student so here I can simply use
let's say print line scholarship status
student dot is scholar right and simply
pass the marks of the student as let's
say 57 so here if I run the code right
now then in the output we will get
something like that scholarship status
either true or false
so here we get the scholarship status as
false and the pass status as true now
this scholarship status is false is
coming from the extension function right
here like this now if I tell you that
this is actually not the practical usage
of the extension function so whatever we
saw right now was just an explanation of
the extension function how do we define
it the syntax is like this now let us
come to the point let us define a
function and check out the practical
usage of the extension function so let
us now change the code now suppose I
define a string let's say STR one of the
type of string equal to hello and now
let us define one more string so here I
have simply defined two string values
string one and string two of the type of
hello and world value and now suppose if
I define one more STR three of the type
of string equal to let's say hey right
now suppose later on in our program I
want to combine these three strings that
is I want to append these three strings
together for example we can simply use
Str three equal to str three plus str 1
plus STR 2 like this so this will work
fine so in this way we can simply append
three strings now suppose I want to
define a function that is I want to use
the string plus to add these three
strings right so what I will do is I
will simply try to find out the solution
by using STR 3 dot let's say I have any
method that simply adds all the strings
together or not so here I do not have
any method that takes two more
parameters and simply add all the
strings together so what I will do is
down the side I will simply create an
extension function that is let us create
a function inside which we will add all
the strings together right so I will
simply create an extension function for
the class of string string dot let's say
add right and now as a parameter I will
simply pass let's say STR let's say
string one of the type of string of the
type of string again right and this
simply return a appended string and now
here I will simply use return statement
and I will simply add this plus s1 plus
s2 now I will explain you right now what
is happening so I will simply use here
STR dot add and simply pass str1 and
str2 right and now let us print the code
by simply using the println statement
STR 3 cut the statement from here and
paste it here and now let us run the
code and let's see what happens
so in the output we get hey hello world
so what exactly is happening here so
here I have simply defined the extension
function of add now this extension
function ad is now a part of this class
of string now this string is actually
the predefined class whose code we have
not written it is already existing in
our SDK ok so we don't know how to
modify this class but in Kotlin there is
a way to do it we can simply add a
function inside a predefined class so
this add function is now is a
part of this class right of the string
right and now here it takes two
parameters string 1 and string 2 and
Here I am calling this method with the
help of this STR 3 now STR 3 is defined
here which is actually of the type of
string now as already said everything in
Cortland is actually a object so this
string 3 is actually an object so we're
simply calling object dot add method so
a string object dot add method right
just in a way that we call any other
method with the help of the object so
this is tr 3 simply calls this method
and simply pass two parameters and
inside this method I am using this plus
s1 plus s2 now this keyword is actually
referring to this STR 3 that actually
holds the reference for the string 3 now
string 3 is actually has the value of
hey s1 has the value of hello and s2 has
the value of void so we are getting hey
hello well together appended and
returned inside the println method and
we are getting the output as hey hello
world right and now let us take one more
example let us try to find the greater
number with the help of the integer
class well X let's say equal to 6 and
then I will simply use Val y equal to 10
now these two are actually of the type
of int right so do not forget this it is
also the type of end now here there is
no predefined function where we can
simply call let us say X dot find the
greater number like that or greater
number we do not have any method inside
the integer class that is this integer
class so for that again down the side I
will simply define an extension function
for the class of integer dot let's say
greater value and here I will simply
pass one parameter because we are having
two integer value 6 and 10 so the first
one will fall here and the second one we
will pass on with the help of a
parameter other number of the type of
int and it simply returns the integer
value right this
is greater than let's say other so here
I have simply completed my code so
inside this method I have written the
if-else condition if this is greater
than other number then simply return the
current number else return the other
number right so if we are calling X dot
greater value and simply pass the other
value as Y right so here we will get the
value as well
greater value equal to X dot greater
value Y and now simply print out let's
say greater value so when this statement
is executed X dot greater value that is
simply going to call this function int
dot greater value which is now the part
of this integer class right and now here
this refers to the value of x the object
that is calling this method the value of
that object is actually stored inside
this keyword right so this refers to the
current reference of the object and now
the other one is actually the parameter
that we are passing here with the help
of Y variable so if the current value is
greater than the other value then simply
return this otherwise return the other
value which is now the greater value so
let us now run the code so here in the
output we have 10 as the value which is
the greater number among 6 and 10 right
so this is the way you can use the
extension function in case of Kotlin now
what are the advantages of using the
extension function let's check it out so
the extension function has few
properties such as they can become part
of your own class example student
employee user and so on and the other
thing is that they can become part of
the predefined classes such as array
string integer care or any other
predefined classes that comes with the
Kotlin sdk right so always remember this
you can make it the part of your custom
class such as student that we saw in
this video and also for the predefined
classes such as string int and so on and
now what are the advantages of using the
extension functions
it simply reduces the code and it makes
the code much more cleaner and easy to
read so it simply reduces code by
allowing you to add add your own custom
methods inside some class so you don't
have to modify your old classes or the
predefined classes for just adding one
function so this is all for this video
about the extension function in case of
Kotlin thanks for watching and have a
good day