Java Essentials - Exception handling in java

In this video we are discussing exception handling in Java

Exception means erroneous condition. Let us suppose I've defined one array having got size of 10, but I want to keep a data

at the 20th location. Then exception will take place. I want to divide two numbers A by B, but B is having the value 0

So that is a source of producing or getting exceptions. Let us suppose I have defined one integer array, but I'm going to be a number

going to keep one string data onto that integer array. So that will produce one exception

So in this way, there are so many different ways or cases where we can have the exceptions

Let us consider another case. We are trying to do a data insertion on a table where the table is not existing

So you see, we are trying to read something from the data file, but the file is not present

in the respective folder or the path is wrong. all these cases the exceptions will be there and whenever such exceptions will

occur during the execution of a Java program then obviously the program will

have will get halted will get terminated at the midpoint so how to handle

this exception and that's why the origination of this chapter there is an

exception handling in Java an exception or exceptional event is a problem that

arises during the execution of a program that means during the runtime of a program

when an exception occurs the normal flow of the program will be disrupted and

the program or the application terminates abnormally a very popular exception is

dividing some number by another variable but the variable is containing the value

zero or dividing a number by the zero directly in those cases exceptions will be

generated so just consider this particular diagram here so here we're having the

class object from the object class this thruble class has got inherited from the

throughable we're having this errors class and these exceptions and from these

exceptions this runtime exceptions and other exceptions will be inherited so in this

way we're getting the hierarchical diagram hierarchical class diagram regarding this exception handling in Java so how to handle exceptions

A method catches an exception using a combination of the try and the catch keywords

So, try block. So after the writing the try keyword, we'll be putting the curly browsers and then we'll

be putting some set of statements there where we are expecting some exceptions may take place

So if those statement execution may cause some exceptions during the execution, then those statements

must be kept under the tri-block and catch-block should follow the try-block immediately

A try-catch block is placed around the code that might generate an exception

We can enclose the instruction like this respective syntax. So try, then code that can generate exceptions, we are guessing, and then after completion

of this tri-block, that is closing of this corlybress, immediately we will be having the catch

block so catch exception name e then within the cul-libres will be writing the respective exception

handling statements that means when the exception will occur then what we are going to do in this way we can have multiple catch blocks in any order which will be following there and these catch blocks can handle individually each and every exception separately

to provide the remedial actions to be taken when the exception will occur during the runtime of a Java program

Another block is used after the try or try catch block that is known as the finally

So codes inside the finale block always gets executed irrespective of the fact whether any exceptions

has occurred or has not so this is the concept of our exception handling so for

the better conception for the better understanding let us go for one practical

demonstration using Java code and we are going to use that one we're going to

give the demonstration right now after this in this Java program demonstration

we are discussing exception handling exception means erroneous condition so within the tri-block we will be writing some set of statements where you are expecting

some error may take place. So here we are doing one calculation that is I and T result

is equal to 22 by 0. We know that division by 0 is illegal. So as a result of that, when

this division by 0 will try to take place, then in that case this line will remain unreachable

unexecuted, the control will try directly will come to the respective catch block which

is just following the tri-block where the arithmetic exception has been caught. So how to write

the catch block within the catch block we'll be writing this the exception name and the exception

object there is a catch the exception and handle it in a correct way we're supposed to write the

respective remedial actions to be taken when the exception will take place and then catch block

will be followed by the final block obviously that is optional it is not mandatory that always the

catch blocks will be followed by the final block in the final block we'll be writing some statements

we can put some block of course there what is the purpose of the

the final block whenever exception will occur in the tri-block then also the final block

will get executed after execution of the respective catch block if that if no error has occurred

no exception has occurred in the tri-block then also the final block will get executed

that means the finally block will get executed irrespective of the fact whether exception has

occurred in the tri-block or not and then end of the program the rest part of the code will get

executed so now let me go for the execution at first you can find that dividing dividing by zero is not allowed so that means this

particular line has got the control that means system dot out of print

and result is equal to plus results so that line has remained unreachable and

then the exception is Java dot land dot arithmetic exception and what is the

error message that is our division by zero so that is the error message and then

operation performed so it is coming from this finery block and and end of the program it is coming from this rest of the line after the try catch finally block so in this way you have got the idea so now let me make it too so that no exception will take place then result is the golden event that means this line has got the control the catch block it hasn't got the control the control has come directly to the final block operation performed that message has got printed and end up the program that message also got printed here so this is the purpose of our

try catch and finally so let us extend this program to some more extent so we'll be

going for the keyboard inputs so we be going for data 1 by data 2 so data 1 and data two will be taken from the keyboard as input so here you are defining some set up

so there is a input stream reader so we shall go for and just this one and it is

asking that it is going for the import so it is under Java.io package so input

stream reader has got imported next one you shall go for buffer reader

buffer reader beer is equal to new buffer reader

isr this is a buffer reader so import has to be done Java.io is a package

name then from this buffer reader beer we shall go for I&T data 1 is equal to

br.d. So I shall go for this readline and it returns string you can easily find

that return string so that's why I must be doing a typecasting here so

this a red line is there and it is taking that is a change of type data 1 to string otherwise we can go for integer

dot parsa nt integer dot parsa nt this particular string has to be

converted to integer and then again one red underline it is indicating that

add throw a declaration or surround with the try catch so surround with the

tri-catch you can find that this particular this particular parse i.n t deadline it has got surrounded with this number format

exception and i.o exception so it has got surrounded with that otherwise you can

write in this way I press control z surround with the try multi-catch so in this

way you can also go for this multi-catch that means number format exception or I

you exception then this respective code will get executed otherwise we can go for

another way other is you can write it it in this way so that is also very much useful also

we can segregate them because we may have different remedial actions to be taken

and there is the final block we are having so we are having this

arithmetic exception we're having this number format exception and then I exception there so let me go for this another data has to be read so let it be

data 2 and you are performing data 1 by data 2 we are performing data 1 by data 2 so now we are having this set of multiple catch

blocks are there so let me go for the execution all the required inputs have been done by this eclipse

Now let us go for the execution. We are just executing the same

So we are executing and then here we are writing the first value, say 100

The second value is a 20. I'm getting the result 5 and operation performed end of the program

So let us go for one prompt here for the better understanding. running

100 second number we are putting as 20 result is equal to 5 is coming if I execute the same if I provide the first number as 100 second number as 0

Division by 0 is not allowed that means the arithmetic exception has been caught and the operation performed and end of the program

Now next time if I put the first number as say 100 the second number has said 10 then number format exception has taken place operation performed and end up the program is getting executed

that is whenever we are providing providing 10 TEN here so that cannot be

converted to integer so whenever you are providing 10 then 10 cannot be

converted to integer because we have written 10 not in one zero format but in

TEN that is in the form of string so in that case in that case this

respective number format exception has been caught here so I want to show you

one thing that instead of writing this particular I'm just making them comment

there's a number format exception and this I'm going for this up to this so now

see this arithmetic exception and number format exception I put them under comment

and then after this catch block we are providing exception which is the

superclass of all the exceptions so this exception and this exception has been caught

has taken place so now what will happen when about this arithmetic exception or

number format exception will take place then exception will handle the situation let

me go for the execution so 100 and 0 you can find that exception has taken place

so now again we are executing this 110 110 you can find that exception has

taken place that means instead of having this arithmetic exception catch block

and then number format exception catch block we can have a single exception catch block that is a

catch exception e exception has taken place the remedial actions are to be written in here and finally

is there always will get executed even if exception has occurred or has not occurred so this particular

example i think has cleared your doubts that what is exception and how to write the exception

handling program in our java code so let me put back my code

in this case. So what about the rest of the exceptions, which I haven't caught here

will be caught by this exception catch block. Thanks for watching this video