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Let's begin by first learning about how exceptions are represented on how they can be hundred.

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An exception is simply an object of the class through habit or one off it's up process.

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So to simply an object like any other good job object on Trouble is from the outline package under the

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superclass of all exceptionally literate classes.

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And as I mentioned earlier an exception indicates an exceptional situation like a partner solver going

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on in such a case a method or a constructor gender's the exception.

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Now let's head over to Eclipse and we will learn about exceptions by directory writing some code.

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I've created a new package called com not semantics.

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There are exceptions within the demo project and within the exceptions package classes have been created

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one has exceptions them all and other is hitcher to be connected and within the exceptions class there

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are two amateur's.

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One is mine and the other is share on the share that is very similar with a shared method that we have

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seen in the in the earlier project.

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So if you recall in Threepio project the sheer method was used to share a bookmark with a fictitious

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partner Web site called good snips.

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And so the shared method is also very similar to that and within the history to be connected with us

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.

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We have this method called Center and the main method actually invokes shared motard and shared method

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in done in Wilkes.

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The sentiment that it's a static method and has GTP connect Ansen method actually does that are real

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sharing of data of it with snips.

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OK so even though share is supposed to do the sharing.

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But the actual sharing will be done by send and it has all the low level details for shading off the

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end of the with the partner Web site.

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OK.

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So that's the assignment.

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So we have just three template metrics in each method.

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We have to print statements one or the top one at the end at the top it says in site for example here

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it says inside me are not the end users end of Main.

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Similarly in shared how insights share on and off each year on scene with the Send method also and these

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print statements have been included in order to look at the control flow.

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So the control flow defers based on whether or not an exception is being has been generated.

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If an exception is generated then you would how one type of water flow.

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But if the next option is non-gendered then you will see a different control flow.

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So in order to keep track of dock we have these print statements.

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And so let's just go ahead and start filling up these methods.

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Let's begin with the sand method and it has three parameters one in parameter on string parameters.

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So here the data is one of the parameters and the goal of this method is to send this date talked with

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a partner up site and destination retailers how the it is going to be transmitted.

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So we have two ways in which the data can be shared.

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So the first way if destination is zero it means that there will be written to a file on the local Sarber

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on the harness and then there'll be some kind of a script which will push their data to the partner

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Web site.

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So that's one way.

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And if destination is one it means that the Send method will programmatically push their data directly

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to the partners partner to the partner site and really push it to its webservices let's say the part

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of several host of absurdest ironed destination is one Sandwell directory pushed their data to the partners

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absurdest.

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OK so those are the two ways in which they can be shared with the partner Web site and exhibitor domain

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but the value their destination has.

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So let's begin and let's just assume that destination is one.

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So in this lesson we will look at only when data is written to the file and through that process we

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will learn something about how exceptions are generated are and how that can be handled in the next

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lesson.

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We will also look at the second approach.

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One destination is to one destination is one and we will try to learn a few more concepts but we not

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going to do any We are not going to write any code for shading off the data like writing good a file

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are calling the passing grade of service that we are not going to do so because that's that's not in

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the context here.

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So you know our goal is to just learn about exceptions and be I just use using this example as a use

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case.

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OK.

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So let's just go ahead and read this here now when we are if we have to write somebody to a file we

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use a class called file output stream which is from the dollar package and is responsible for writing

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the report with a fine.

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Now if something goes wrong when writing the data then an exception will be generated by the file output

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stream class.

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OK but the exception will be generated by that particular class.

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So if you just use that class you're not going to learn about how an exception can be generated.

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Correct.

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So the goal for us is to see how we can generate an exception because we are still learning a lot about

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the exception generation process.

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So let's just assume that we are trying to write the data file and somehow the file is missing.

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So we need to generate an exception.

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So that's an exceptional situation.

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We say that exceptions need to be generated only an exceptional situations.

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So in this case the exceptional situation is that there is no file and the file is actually missing

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and we cannot write that out with that particular form.

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So that's an exceptional situation.

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So in this case we need to generate an error and an exception.

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So for that we use something called a troll statement and it starts with a rookie.

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And we said that an exception is basically an object of the class through mobile or one off it's subprocess

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.

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OK.

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In this case B the subclass is called as a file not found exception and that's the exact class that's

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also used by the file output stream class.

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OK so if there is any error it generates the file not found exception.

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So let's just use that class on gender to an instance of doc of that particular class

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and it's giving a compiler error because we need to import it and it belongs to the IO package.

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OK.

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And it is a subclass off trouble and trouble is the superclass of all off all exceptions.

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But it still gives a compiler error.

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And that's because this particular method is generating this exception and there is some other code

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which is invoked which will be been working this matter and that in working code needs to know about

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this particular exception.

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OK so here in this case this exception is being generated within the body of the Send method.

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So it's an implementation detail but how will the in working code know about this particular exception

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.

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It needs to somehow know about it.

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Right.

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And for that we need to indicate that this particular method might throw this exception and that we

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need to indicate that here in the in the in the method declaration itself.

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So if I hover over it it gives me two options as one handle exception type unhandled exception type

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either use surrounded with a quick catch but we will see later or add to this declaration.

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And this is what we are going to do not now.

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So it I it has added this exception to the declaration and it uses this keyword called Astro's.

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OK Andreas can be followed by one or more exceptions.

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OK.

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So there is no more compiler compilation error.

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So in all this and motard is saying that I might throw this exception also.

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OK so that's what it is informing.

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Any indication.

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But if you go back to exceptions demobilize from the sheer method we are invoking the Send method and

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this NABC a completion error here also.

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And that's because the Send method has to handle this particular exception.

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Now if I have got over it we again see the same options here.

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It says either our throws declaration or surrounded with a try catch.

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OK this time let's pick this up and once we look at that we will look at the first option also.

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When I do that we have a try catch block here.

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It's also called as an exception handler and the Send method is engrossed in the try block.

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And there is a catch block here on the catch block has a parameter here called filing not found exception

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.

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OK.

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So as you can see it looks very similar to we are calling it as a parameter.

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So in that sense it is very similar to a matter.

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All right.

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You can't know within the.

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This is the body of the catch block.

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And here it's invoking a method called blenched daiquiris.

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OK.

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So this is the exception handler.

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So if you want to write any recovery code when an exception is generated You need to write it here.

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So basically an exception will be generated in the Send method and that exception will be handled here

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.

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So let's just go ahead and run this thing.

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So as you can see if we initially were inside main then main is invoking share on Share is invoking

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send.

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And here you are passing zero.

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So this needs to be zero here.

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Let me just read on it.

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Now you can see that within inside Senator.

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So destination is zero.

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And this statement is getting executed.

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And as soon as this statement is gets executed the control goes back to the to the invoking method which

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is share.

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So the rest of the method is good to hear.

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OK.

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And this particular method and off center is not being rendered here only no share on enough meanness

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here.

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So the control goes back to the calling method.

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So this method will be popped off the stack and then controller comes here.

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And so then the exception is generated the exception of riposted the JVM and JVM and see if there is

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an exception handling code within this method.

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I know it's not there so.

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So it pops off this method from the from the call stack and here it tries to see if there is an exception

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handling code and there is an exception handler here.

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So it just it just passes the exception object this particular pyramided it assigns it to this barometer

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underpins the message.

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And this is nothing but as doctoress basically does it gives information about the type of exception

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here which is a file not found exception and it also gives her radius off the exception are sort of

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created God generated initially on how that particular method got in.

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For example here it says that the exception most generator that has strictly be connect at line pen

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within the history class on that particular method was invoked from share method or here at line 17

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.

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That's very.

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This meant that method was invoked and shared was again invoked by another method main.

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OK so that's how you have done to try and catch block.

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This is how you handle the mechanism.

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This is how you handle exceptions and you would have some recovery code here.

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OK.

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So if an exception is generated it means it's generated in some exceptional situation in which case

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we handle it.

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And so you would have some recovery code here now.

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So there is.

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So you had this we thought this strike would be what we were getting a compilation error.

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So the next step is if you are not handling it here and if we want to why compiler error then shared

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method can actually can actually relate the error.

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Which means it says that I'm not going to handle it much.

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The Invoking method might be able to handle it.

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So I'm just going to relate back with my main working mother.

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OK so let's try that option also.

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So in this case let's pick the first option as you can see it's the truest gloss has been added here

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and the compiler is here.

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So let's start on this share method with try catch block knowledge's just go ahead and look at the control

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flow.

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So you are inside.

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Here you are inside us and then an exception has been generated.

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And so this statement is not getting executed here Anderson method is bumped off the stack and control

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comes back here and to the class and sees that the JVM sees that there is an exception handler here

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.

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So it's not going to even bring this statement and off share.

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And I do not support the sharing method from the call stack and then it will go into the main method

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and see if there is an X if there is a class here.

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If there is an exception handler here and it is here it's going to print this thing.

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And after the catch block then this statement will get executed and off Maine will get executed OK.

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So you can see the control flow here.

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Now so after the catch block is executed then the statements following the catch block will be executed

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.

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Now if he'd come and this out the only other thing or only other option as the main method would also

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have to throw the exception.

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But then in which case this statement will not get executed.

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So in none of the statements will get executed because the the keep the JVM keeps popping off those

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and those methods off the stock.

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And finally it gets here it also pops this off and there is no other method to handle it.

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I enjoy them also.

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But you know it gives up and the program dominates.

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Now if this is if this was a web application with hundreds of threads running simultaneously then one

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third will be handling one user request and with in that case if such kind of an exception is generated

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if it does not handle finally that that particular thread that belongs to that user will be terminated

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.

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OK.

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So this is what we have here.

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And and here one thing I can show is you can also have this and this particular gadget and actually

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read toerag even this can be done.

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So which means that control comes here.

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But then this is going to read through it.

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And then it needs to the main hospital still handle it OK or it needs to just you know relay it so you

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can also catch block and also to an error.

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So that's about it.

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So we have looked at the exception generation on handling process and then the next lesson we will also

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write the next block here for Destination equal to one and we'll try to explore a little bit more about

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exceptions.

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OK thank you.

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And you can find the court and the resources section for it.

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If the files do not how bargello extension and if to not be XDR or some other exception extension just

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gone what did Kadar Java and you can compile and run it.

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OK thank you.

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See you in the next lesson.

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Unhappy according