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Welcome back in this video, we are going to check out exception handling, which means the handling

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of runtime problems which occur in the program and what otherwise leads to program termination.

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So this is the case for not only apps, but for all programs.

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So what is an exception?

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An exception is a runtime problem which occurs in the program and leads to a program termination, which

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on the phone means that the app is not going to respond.

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Now that is a very, very bad behavior.

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So you should at all costs, try to avoid exceptions to not be handled.

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So just to just run.

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So examples would be running out of memory array out of bounds condition like divide by zero.

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And you handle this type of problem during program execution.

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The technique of exception handling is used and exception handling is a technique which handles the

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runtime problems and maintains the flow of the program execution.

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So when you use exception, handling the exceptions may still arise.

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But they will not make your program crash and your program will still work, even though it might not

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do the things as intended.

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For example, if you try to access the internet and you don't handle the exception that the internet

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connection doesn't work, then you would run into an error and you would get an exception because you

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can't connect to the internet and that could break your app if you don't handle this exception.

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That's why it's super important to handle those kind of exceptions and yet still make your program work.

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So even if the internet doesn't work, then you will just display something to the user.

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Please turn on your internet or get an internet connection or something like that.

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All right.

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So there is a third world class, which allows us to throw an exception.

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So this throws an exception if we're used as through keyword and then the name of the exception, I

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call this exception my exception, because we can create our own types of exceptions, which will then

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do whatever we want to do in those cases.

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There are four different keywords used an exception handling.

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And these are try, catch finally and throw.

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So these are the main keywords, and we're going to check those keywords out.

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So keywords used an exception handling.

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Let's look at the try keyword to try.

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Block contains a set of statements which might generate an exception.

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It must be followed by either catch or finally or both.

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All right.

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So this is the code that can break, that can make and more create an error, create an exception such

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as connected to the internet or running through an array.

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So that can be a lot of issues that come up.

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Then the catch block is used to catch deception thrown from the tribe.

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So if there is an exception in the tribe block, the catch block should execute.

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Otherwise, it will not execute.

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So if there's no problem in the tribe lock.

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So if the code works perfectly fine, for example, back to our internet problem, let's say we have

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internet and we try to exit the connection, then we will not have a problem.

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The try block will work, the catch block will not execute.

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But if the internet connection is not there, then of course the catch block should run.

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Then we have.

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Finally, the final block allows execution, whether exception is handled or not.

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So it is used to execute important code statements like closing buffers, for example, closing a buffer

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which takes care of the connection to the internet, or a buffer that takes care of storing data on

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the phone.

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So these are things that need to be closed after they have been opened and that is usually done.

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And finally, so after the tribe lock has been executed or after the catch block has executed.

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If there was an error and then we have this through keyword, which allows us to throw an exception

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explicitly so we ourselves write this in order to throw an exception in order to cause an error.

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And this is especially useful when testing to see where an error occurs and we create our own exceptions

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or throws so that we know, OK, this is something that we just wrote, All right.

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And then there you are, sitting in front of your code and suddenly an exception arises.

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Well, the thing is that usually happens when you have unchecked exceptions.

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So an unchecked exception is the exception, which is thrown due to mistakes in our code.

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So our code for some reason doesn't work, and there are multiple different exceptions, and the exceptions

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don't run during runtime or execute during runtime or runtime exceptions.

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And they extend from this runtime exception.

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Class of the unchecked exception is checked at runtime, which means when our app is running and not

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during compile time, meaning when we compile our app and press, for example, the run button.

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Examples of unchecked exceptions are arithmetic exceptions thrown, wouldn't we divide a number by zero,

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for example, then the right index out of bond exception is thrown when an array has been tried to access

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with incorrect index value.

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So let's say the array only has five values, but you're trying to access to sixth or seventh value.

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Then you get this error.

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You can very easily try that and force this kind of an error.

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And you probably have seen this already.

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And then there's security exception thrown by the security manager to indicate that we, yeah, have

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a security violation.

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So for example, we're trying to access GPS, but we don't have the rights to access GPS because the

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user didn't give us the rights to use the aGPS functionality.

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And then the very common null pointer exception thrown when invoking a method or property on a null

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object.

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So when we tried to access an object which is empty, which is now, then we get this null pointer exception.

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And that is something that I have already talked about when we looked at numbers.

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Then checked exceptions.

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Well, they are acceptance, which are checked at compile time, so pretty much in our code, we write

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this ourselves.

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There's exception type extends the throw bill class, so there's a class control bill, which takes

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care of the exception.

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Functionality and examples of exceptions would be the input output exception.

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So i o exception or the sequel exception?

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And there are a bunch more.

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Now let's look at the try catch block, which is used for exception handling in the code.

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The syntax of try with catch block looks like this.

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So we have this try then code that may throw the exception and then we have this catch.

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For example, some exceptions.

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So this could be the Iowa exception if it's an input output exception, or it could be just a generic

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exception.

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So we would just use the generic exception clause name here.

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And then we have our code that handles the exception.

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And of course, we need to close the bracket here.

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All right.

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Examples without exception handling.

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So in this case, we have an exception handling Britain ourselves.

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So try and catch.

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But the exception is never arising because the problem doesn't appear.

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So here, for example, we use value string get.

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No.

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So we use this function, get no, and we have a value of tender.

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So the variable string is getting the value of 10 and then making a string out of it.

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So we're trying to integer parse it.

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So we're trying to parse that value into a string.

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So it's an integer, right?

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10.

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But we're making a string out of it.

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And if something goes wrong, for example, an arithmetic exception appears, then we want to output

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zero.

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All right.

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So if we run print and string now we get the output of 10.

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All right, now, let's look at the exception handling when it's actually running.

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So when we actually do have an exception handling running, and that is the case, for example, if

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we try to have a parsing here with a value of ten point five.

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So in this case, we're trying to parse a double as an integer, and that doesn't work.

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So we have to be careful with the type here, of course.

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And that creates an error.

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So our try block does actually create an arithmetic exception.

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So the output is zero.

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So whatever we have in our catch block here.

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All right.

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So that is something that we, of course, have to be careful with.

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Then we can have multiple catch blocks so we can use multiple catch blocks in our code.

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And they are used when we can have different types of operations or have different types of operation

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errors in a tri block, which may cause different exceptions in the tribal.

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So here's an example.

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We have this function where we try.

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To get the value a out of an interim, which is five, so which has five elements in there.

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And now we're saying a at position five, which are at Index five, which means at its sixth position

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should be 10, divided by zero.

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So there are a bunch of problems that we create here.

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One of them being that 10 cannot be or anything cannot be divided by zero.

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So we get and I really the exception here trying to divide by zero.

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Not good doesn't work creates an error.

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And then we're trying to access an array at a position which doesn't exist.

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So the array just has five values, but we're trying to access that sixth value.

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So we're creating this problem here.

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So here this is where the problem arises.

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All right.

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So we have two arrows that can appear here, and then we have the arithmetic exception, which takes

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care of arithmetic more than we'll just print of my take exception catch.

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So, for example, trying to divide by zero, then we have an array index out of bounds exception,

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which will be run because of this, a accessing index five.

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And then we have a generic exception, which is the apparent exception clause.

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So it's just the name exception.

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So you can see in catch, we always have this e colon and then the name of the exception that we want

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to use.

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And by the way, you can get information about the arrow.

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So a little more information or pretty much so a lot of information when you just print the stack trace

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of it.

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All right.

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So we can see that the output here will be an arithmetic exception catch.

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And then we have the code after the try catch.

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So we can also have nested try catch blocks and that is sometimes required.

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But the requirement of this to try catch blocks arises when a block of code generates an exception and

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within a block.

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Another code statement also generates an exception.

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So that is the exception inception, so to speak.

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All right.

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Syntax of nested try blocks.

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Let's look at this.

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So we have a try code block and then we have another try code block and then we have the catch block

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for the first try and then add some exception code that we have, and then we have another exception

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that we catch.

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So as you can see, the try has to be followed by a catch.

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But when you have a try inside of a try, that's try has to be followed by a catch.

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OK, so these two are connected with each other.

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And this try here is connected to that Cacho down there.

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All right.

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So this is an example for that.

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Then we have the final block and you saw the keyword finally before and to finally block is such a block

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which is always executed, whether exception is handled or not.

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So it is used to execute important code statements.

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For example, as I said, earlier code that should be run when all of the other code just done, for

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example, closing the connection again.

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So we have this function main here where we try to divide the time by five and then we print the data.

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So our catch that we have here is a no pointer exception catch.

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So.

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We have this exception that we pointed here because data could be empty, for example, and then we

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have this finally block here, which always executes and then we have a print line below code just to

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see what's executed.

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And if we run this code, we will see that to then finally, block always executes and below code are

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printed onto our console, and that has to do with first of all, ten divided by five is two.

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So this print statement is printed.

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Then here you see we print the EA, so the null pointer exception.

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So if that would arise, we would print the whole exception.

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And then we have this final block, which is executed no matter if try is running without an error or

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if it's run with with an error, so the catch block will be run as well.

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So either way, we run our finally.

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So our print to finally block always executes is executed.

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And of course, our below code is also executed.

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Then we have this throw key and throw keyword is used to throw an explicit exception, and it's used

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to throw a custom exception, for example, to throw an exception object.

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We will use the throw exception, so the syntax of the keyword is throw some exception.

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And let's have a look at for this or we have this function where we use this validate function and we

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add the value of 15 in there, or we pass a value of 15 and we print some code after the validation

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check or pretty much after the validate function.

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So in the validate function, we check if the age is below 18 and if that's the case, then we throw

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an arithmetic exception where we say under h.

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And if the age is not under 18, then we say eligible for drive.

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So this is not the case for the US, but it's the case for many other countries where you have to be

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18 in order to drive.

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So the output here is exception.

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Infrared main java the length that arithmetic exception colon under age.

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So after the column comes, whatever we have entered in those brackets.

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OK.

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So in our case, under age.

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So this is something that comes in handy when you actually want to make sure that you check your code

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correctly and you just want to throw these kind of errors in order to break your code in order to understand

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where the problems arise.

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So in this case, it wouldn't make sense because it's a dumb example, so to speak.

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But in real life, it would make a lot more sense when you, for example, need to check your app.

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For potential incorrect entries that users can make or for potential problems that arise when you get

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data from the web and stuff like that.

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And you don't want to publish the app with a lot of throw statements or a lot of errors.

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Okay, because a throw statement actually makes your app crush.

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All right.

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Now let's get back to coding.

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This was a super long example of the whole concepts of try and catch blocks, but now you know pretty

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much everything about it.

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And we can use it in our code.

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And all of this might look a little intimidating, but it would really become your second nature once

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you use it and you see what the advantages of all of those things are.

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So I think let's get back to coding and see in the next video.