Java Programming Tutorial - 82 - Exception Handling Video Lecture - Java

what is going on guys welcome to your
82nd Java tutorial and in this tutorial
I will be teaching you guys about
exception handling
now what exception handling is pretty
much a way to handle errors now an error
and an exception are the exact same
things so pretty much why would we want
to handle an air well when the user does
something they're not supposed to do we
don't want to get in error or else the
program which is shut down and it will
stop running we want a way to do
something like if they like divide by
zero or click something you're not
supposed to click then we don't want the
program to shut down and we want to be
able to tell them they're wrong and tell
them to fix their mistake so let's go
ahead and I'm going to use scanner so
I'm going to go ahead and import Java
util dot I'll just import everything
because I'm lazy and now let's just go
ahead and let's begin making our system
so scanner I'm going to name it input
equals new scanner and as parameters
type system not in and now we have an
input variable called scanner so what do
we want to do well let's just go ahead
and make a little program 2/2 number so
system.out.print line and go ahead and
print like just give them from like
enter first num and now for the first
number in to number one equals input dot
next int BAM and now whatever they type
for the first number is going to be the
let's see numerator and now let's go
ahead and copy this duplicate it and go
ahead and set this equal to num2 and
give them a new prompt and our second
number and now let's go ahead and make a
new sum equal to num one divided by num2
so now we got a little program if we go
ahead and print out the sum so
system.out.print line
and go ahead and print the sum and we'll
run this and test it make sure it's
working so as I say number one oh here
we go so now let's go ahead and test
this real quick and see if it works okay
and our first number 12 and our second
number three and it gives us an answer
or four so this works fine but if we run
it again and we go 12 in for a
denominator we give a zero remember you
can't divide by zero it gives you an
exception like this so this pretty much
shuts down our whole program and what if
we build a huge program for like
analyzing stock market and that was
awesome and then some idiot tried to
divide by zero and the whole thing just
shut down well that wouldn't be good so
we need a way to kind of handle these
errors until the user R right don't do
that but we're not going to shut down
program we're actually going to fix your
problem well in order to handle
exceptions you need to learn something
called try and catch what try and catch
means is it pretty much like pretty much
just like it is you try a bit of code
and if you have an error you're instead
of shutting down your program you're
going to catch that error and do
something with it
so here's how you do this go ahead and
put try and that's a key word in in your
curly brackets fill in the code that you
want to try so I'm going to try this so
in my try block right here I'm going to
write the code that I want to try so I'm
going to go ahead and try this and what
this tribe means and what this code
block means if you have an error
anywhere in here what we want to do is
catch this error so go ahead and write
catch after this and there always needs
to be a catch after a try and there can
be something called finally - but for
now remember there always needs to be a
catch after a try in for catch what do
we want to catch we're going to want to
catch all errors and in order to catch
all air errors remember they're called
exceptions type DX
cep tion ii and why do you need to write
this there's actually different types of
errors like arithmetic err I think one
is called like input error or something
like that but the like if they make a
math error or if they click something
wrong they're different types of errors
but if you want to catch all of them
this means if they do anything wrong at
all this is just the broad exception
class right here so let's just go ahead
and catch that in the e is pretty much
if you want to print out or something
like that but if they have any errors
what do we want to do let's type
system.out.print line we'll just type
something like um you can't do that and
let me fix this so what this pretty much
means is try this if you have an error
do this if not if you try this and it
works good then this is never going to
run at all so let me show you that I'm
going to try this and I'm going to enter
12 3 BAM
for this catch right here never runs it
all but if I run this again and I get an
error and it says 12 0 it says you can't
do that in my rest of my program if I
had any more code down here it would
continue to run normally so what if I
actually wanted to build a program so if
they entered the wrong thing then I
could pretty much have them do it again
over and over again until they enter the
right thing well let's go ahead and this
is really simple but it's x equals 1 so
I'm going to pretty much have a do-while
loop and I'm going to do this do the
pretty much the whole trying catch so
catch this and want to catch that too I
want to do the whole trying catch while
X that we just made that's equal to 1 is
equal to 1 so I'm going to do that over
and over again while this is equal
one but the thing is if it continues to
execute successfully and I'm going to
set this equal the X equals two so as
soon as it runs successfully I'm going
to set this X equal to two and it says
all right that's the point in time when
I stop so here is a way where we can
keep running this program over and over
again until we get the right input so if
you had a really dumb user the program
would look something like this run
sample all right and our first number 12
um 0 oh you can't do that try again ok
and our first number again let me expand
this a little bit arm
43 of 0 oh nope you can't do that enter
first number again and it's going to
keep trying and trying so let's go ahead
and do this right so put like 40 and 10
BAM
4 so that is how we can keep kind of
prompting the user to do it correctly
and let me review this one more time how
I did this is I pretty much put all
right what do I want to do over and over
again well I want to try this code and
if this code runs successfully I'm going
to change this variable but if this code
does not run successfully then I'm going
to print out an error and this never
even runs since you get an error in this
in this and when it tries to divide the
sum this is where the error happens
right here on this line so this X never
gets set equal to 2 so that is why X is
still equal to 1 and that is why the
do-while loop is able to run over and
over again but as soon as this whole
thing okay good good good good good good
BAM we finally made all the way X equal
2 and then it looks all right is X equal
to none
X equal to 1 nope all right then we can
finally exit this bad boy so that's
pretty much your basics of track catch -
pretty much I mean it's pretty simple
try this if you get an error
do this I mean how easy is that um
there's actually a little bit more to it
and I'll probably be covering the next
tutorial
but for now thank you guys for watching
don't forget to subscribe and I'll see
you next time