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In this video we are discussing user defined exceptions

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In the previous video we have discussed built-in exceptions. That means
those exceptions were predefined and pre-retained within the Java program

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So now in case of user-defined exceptions,
we can create our custom exceptions

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We can write one class and the class should inherit
or the class should extend the exception class

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And that is the common practice while defining
user-defaults. defining user defined exceptions

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Programmer can create custom exceptions and
they are known as the user defined exceptions

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To create an exception, we need to define a
class for the exception and extends it to the

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exception class. As I have mentioned earlier, that if
I define one class, the name of the class may be my

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exception, but it is of a common practice
to make the class extending exception class

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so that I can define my custom exception. When
we need to generate the newly created exception

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we will use the throws keyword for the method and it
indicates that the function can throw an exception

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So in our code we'll be using throws keyword
which will indicate that this respective function

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can throw some exception in our
code. So this is the concept

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So for the better, clarity on this concept let us
go for one practical demonstration where we'll be

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creating user defined exceptions and we shall explaining our code into a better way let us go for
a demonstration on user defined exceptions here we have defined one class the name of the class

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is below age exception which extends
the exception class here and this is a

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constructor and this a constructor of the
class below age exception and from this

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constructor it is calling the best
class constructor here the best class is

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exception and the best class constructor has been called using super passing
this argument string as input argument so age is under 18 we've defined

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another class the name of the class is application where we're having this
name course and age so three instance variables we're having application is

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the name of the constructor which is
taking this name and the course as input

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argument so this name and course the
instance variables are getting initialized

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here age is also getting initialized
with the default value of 18 this is

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non parameter as constructor obviously the
name of the constructor will be same as

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that of the class name so the name of
the constructor is application which is

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non parameterized and from this non
parameter as constructed we are calling

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the parameter as constructor so these
null string comma null string so here you

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can find that this this is actually
referring to this parameter as constructor

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which takes two string objects as input
argument and here we are passing this

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to null strings here so now we
are having another method that

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is the set age which takes this age as input
argument and which throws the below edge

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exception which throws the below age exception when this input age the input argument age is less than 18 we are
throwing this throw new below edge exception so you are throwing this below edge exception exception class object

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so we are throwing that one so that's
why this function is throwing below age

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exception otherwise this age which is
not less than 18 will be assigned to the

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instance variable age so these dot age is
equal to age now these are display details

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another method we're having that is a member
function so here we are printing this

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name the codes the age and so on so
now let us go for our class that is the

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user defined exception this a main
function here we have defined two objects

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under the application class two objects
one is the application one another one

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is the application two so this is our
respective and name so we have passed this

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John and Java programming so this name
is nothing but this is variable is

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this input parameter name will get
initialized with that value whatever is we are

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going to pass and the course name will be
initialized with this Java programming

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so here this is my name and this is
the course name we're having so now

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application one dot display details so
the display details will be printed here

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so now application 2 dot set age 17
you can find that here we have passed

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the age 17 which is below 18
so as a result of that these

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applies this set age this particular method
will throw this particular method will

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throw below age exception so that's why
we put this line under the tri block

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and tri block is following is being followed by the catch block immediately so below edge exception
e is the object of this below edge exception class and within this catch block we writing this e

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dot get message and e.d. print stack stress
so now let me go for the execution of

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the same so if I go on executing you
can find that the name of the student is

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John and applied for Java programming
and taking the default age 18

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so now in this case what is happening so the
application one dot display details it is

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printing accordingly so in that next
time when you are going for this set age

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method will be called from this application
to that is the application class

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object passing this input argument as
17 so as the 17 is less than 18 so it

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is throwing new below age exception so
automatically the catch block will get

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the control because this catch block is actually handling this below
edge exception e and the respective code is getting printed so e

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dot get message is printing
this age is under 18 and e

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dot print stack stress is printing the respective
outcome. I'm going to show you the outcome here

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So this outcome it is going to show. So you can find
that the error has occurred at the line number 44

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So you see at the line number 44 the error has
occurred and line number 24 is actually throwing

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this below edge. you can find that this line
number 24 is here and 44 is here so it is a the

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respective line numbers are getting
printed so in this way in this particular

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demonstration we have discussed how we can define user
defined exceptions thanks for watching this video