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Hi there this is determined to little.

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Now let's look at this recommendation from Effective Java.

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It is like I'm going to read.

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And it says Do not use a rock by halves.

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And you could sign any code that feel few right now which should not be using what archives.

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So let's go ahead and look at what a rock is.

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We know what a genetic type is.

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And we also know what a parameterize like this barometer or stripe is simply a genetic type followed

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by that type argument.

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Right.

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And the rabbi is also a genetic trait but without any following type argument.

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And here is one example.

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List is a genetic type but here we are instantiating it without using that type argument.

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So we have a rock here and here is another example where the metal barometer is it not.

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I know the problem here with using it wrong type is we would have the same behavior as we had before

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.

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Genetics was introduced that is compile time types if any is lost on we may run into runtime exceptions

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.

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You could type safety problems in the interrupt really some of this chapter we looked at how using object

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as a type can lead to runtime exceptions.

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If you recall for example it was because object type allowed us in replacing dollar Dokoupil or did

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object with our DOT DOT DOT object on later or some other part of the code.

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It led to a class Kostic section.

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And that's because the developer who inserted a jot or tittle or data object was expecting a dollar

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Dokoupil or data object.

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But what he got was a Java.

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A secure and or data object.

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And that's because some other developer has research to object to Jaguar not ask your daddy.

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And that black boot cost an exception.

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So he said that using genetic type gives you the benefit of avoiding such runtime exceptions.

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However if the current code still uses have R-Type than the benefit of generics is lost on we know that

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you should try to detect most of such errors at compile time excellence rather than runtime.

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And in that aspect Jenrette explains a very important role here is that realistic example.

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Let's say we have developed a competitive shopping engine which for a given item fetches the price information

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from multiple partner sources.

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This would allow the user to buy the item from the source that offers the lowest price.

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Here let's assume we have four different classes which are depicted using blue circles.

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Honestly the four classes are part of a data integration component.

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OK so the data integration component is responsible for integrating data from multiple sources.

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Let's say each of these classes are responsible for fetching the price information off a given book

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from one particular source.

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She had the four sources are Amazon Barnes and Noble have dot com and check on the user enters and there's

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the book title in the browser.

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We get the corresponding ISBN which is basically a unique number for the book on the Bassett along with

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an MBA.

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Idlest object to each of the individual objects that are responsible for fetching the price and the

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method is appropriately named as price not out here to see my object is passed to the get price method

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of each of the objects on the list object would be populated with the price information that is extracted

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from the corresponding source.

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No here to cut a declaration would be to get price signature on the left side where the Christ like

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is used.

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But let's assume the developer who wrote the method in the third class which interacts with half.com

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has used a rock on the Bedacht we would run and we are an exception.

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Let's assume that in the court this is how it looks like.

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Let's say you have this method called fetch data which takes an ISBN of a particular item unfetter the

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price information from all the different sources.

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It just creates an our eldest starting the price information that is fetched from the different sources

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.

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The price information would be off by double as you can see to fetch the price information from Barnes

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Noble.

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It uses the class card be an integrator where B and stands for Bunson noble and in works its get price

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method.

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Similarly it also in books the get price method in half and degrader to fetch price from have not come

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on let's assume that this is the code for get price in half integrator.

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And as mentioned earlier raht type is used here for the second parameter in the first statement.

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You may umed that we are in working of episodes of half dot com are not passing the ISBN.

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Let's assume the method in most of Apso based on parts of the price information from the response under

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don't set the price information is off indeed.

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Under developer access to the prices are less without converting it to had doubled since the idealist

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is apartheid it happily accepts that and no one's concordance returns from get price motet the price

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written by half dot com is being extracted.

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And we know that it would give us a cost cost exception because the compiler a place an implicit cast

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on price which is of by and cannot be converted to a double.

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So we lost compile time typesafe the benefit that a genetic type offers just because of using a rock

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I get by method in half and integrator must have used a parametrized.

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In fact even the compiler would give a warning if a rock type is used.

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We will look at that in a short time so that we will do next.

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So using it type is dangerous.

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OK so the next question would be why did the language designers support her archives.

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They should have made the compiler through an exception and the reason it was supported was for the

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sake of interoperability that legacy code Gen X was introduced almost a decade after Java came into

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existence.

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And so there was tons of Java code that was already written Sarnoff methods were using collection pipes

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as pipes for parameters and they all have to work with the new code.

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So the hot water all types.

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But in any new code that you write you must not use the archives as item 23 to commence although you

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should not use archives.

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There are only two instances where wrought by must be used.

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And that has to do with type in Asia.

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And here's a first instance wrought by have to be used in class.

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We know that such a class literal would return the corresponding class object.

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So the first example of it a raw type is used is valid.

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The second example with a parameterized type is used is invalid.

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So we get a compiler error here and here is the second instance we must use start type when using instance

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of operator here in the first example we are checking if object reference or is an instance offset and

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it needs to get Rotty in the second example.

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It is a parameter Christ type.

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And it would give us compiler error.

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So these are not exceptions to the recommendation that are rock types.

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It should not be used in new code.

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Not that I don't want to eclipse to do a short demo.

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OK here we are in the genetics demo class.

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And a new method has been written called rock type dust or this demo.

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So let's go ahead and look at what it has.

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So the best.

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It has the same example that we have seen in the slides.

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So here we have an ISBN number.

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It's on my S-B a number on B how the idlest object which will store the priceless information.

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And I think that we how only half and degrader on we are invoking the get price method that ISBN as

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well as this crisis list.

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OK.

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It's a list of double in the lecture we said that this wouldn't be popular with all the price information

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of this particular ISBN and the place also to extract it from different sources.

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And here we have only one source.

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So let's go here.

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And this is a half integrator it's simply a class in the same class generics Adem on and it's a static

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Mod. undertakes ISBN.

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And here is the prices.

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Here is the wrong pipe.

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And we should not be using it.

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So here if a house or whatever the compiler says that this is wrong.

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So it's giving us a warning.

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This yellow line here it says reference estrogenic bitless E should be parameterised.

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It's giving us a warning that it's not safe to do that.

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Who can hear.

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We are simply adding an A.

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This is supposed to how only double but we are guarding an ant and if we go back we are once again after

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they will Keeshan we are extracting the zero element which would be the price information.

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And it is being assigned to the price which is of double because they're double up he's expecting it

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to be doubled.

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OK.

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But this will give us a runtime exception class cost exception because we know that the compiler would

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have inserted and Bissette costs to double.

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So if we run this as you can see this is the output we are inside Iraq type test and this is from the

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previous demo.

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So it's this classic US exception Jaguar Dorte land are in danger which is inside the place is data

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structure cannot be cast to outline or double.

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So we should follow the item 23 It says Do not use rock pipes in your code so it should have been put

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on Christ type.

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OK.

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And if we make it up but I mean Christ type here if we see of double.

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In this case we get a compiler error because we are trying to add an 8.

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So compiler will not allow us to do that.

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So let me just delete it.

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You can go back.

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Now lets look at the second example here.

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OK here we how clueless all strengths.

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The first list has a b and c and the second has B C and D and we have this method called us get called

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one element elements called which basically gives us the calling off the number of elements that are

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in common between these two.

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OK here we have B and C B and C Those are the common elements 2 elements.

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OK and let's look at this matter.

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You get common elements gone.

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This is how it is.

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Once again it has it all type.

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And the reason I included this example is because generally a purse especially a noodle or perks would

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be good to use rock type if the method is very generic.

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In this case it's giving the number of common elements between the two us.

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Now the elements can be strings or integers or doubles or whatever.

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So it is a very generic method.

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So in such a case developers might be tempted to use the archives we run this.

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So in this case it's just that I'm in contest too because there are two elements in common here.

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So for this there is always the risk of the role of inserting something in while there's less.

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OK.

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And in the calling code that hoper might run into runtime exception that may be rare but it is always

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possible.

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It depends on the car in the context on the matter on the upper.

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So you never know.

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So we should not be using our types as the as the item quoted we suggest.

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So in such a case where we want to have the matter is very generic and we don't know what the limit

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is or we don't care.

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So that is when the tol'able might be dumb to use this but the recommendation for such a scenario where

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we do not know what the limit is or we do not care what that amount is is to use something cart unbonded

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wild card and that is something we will see in the next lesson.

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All right then.

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Thank you.

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And this Dischord is available in the resource section.

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Happy Coding