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Hi there.

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Welcome back.

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This is Duminy loop.

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Now we're going to do them all off the genetic markets and we are going to test out pretty much everything

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that we have seen in the previous lesson.

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So here we are in the genetics class under a new method called genetic math that the devil will has

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been Ardit our Niccol been walk from the main matter.

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In fact we are not going to run this method will mostly look at only compilation errors.

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That's what we'll be doing.

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So here we will look at many things like We will look at the type argument inference we are motard arguments

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and also the type argument input and we are target type.

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We will also look at explicit type arguments justification.

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We will also look at generic constructor and we would also look at the aggregate mattered.

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If you recall in the Wild Card them all there was an aggregate Metford which was not gambling properly

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.

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So Google fixed that and this using generic methods.

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So we also look at that.

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So let's get started now and let's look at this thing called S-type are our inference so everything

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has been written and this particular method in the interest of time.

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So you're not going to write any new code because it is locked or demonstrative here so here.

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So this is the type argument type or inference.

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So it is pretty similar to the method we saw earlier.

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So here it's a static method and it uses this type barometer deep under written byte is void.

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But despite parameter D is also used here as a matter of experimentor type and we're just printing the

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name of this object in this way.

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Plus on Dot get name which give us the simple name.

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Now let's go back.

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So in this case a double is being passed.

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OK.

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And the.

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Type argument that is inferred is from this from the method arguments.

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So we are going to infer it does double.

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So if I how know what hit my Eclipse editor is showing declination of the method which says that the

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type argument invert is double on the same double is also being shown here as a moderate parameter.

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So eclipse is doing that for us.

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It is showing this nicely.

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And then once the the code will be available in the resources section on everything all the comments

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are included.

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So you can also look at all the comments and you get a chance.

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And in the second example we are passing a string Djala.

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So that type in four is string.

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Now here there is a very similar megger it's named as type or inference.

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Only one is added here.

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So in addition to the methode here in the in addition to the method parameter the type parameter is

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also used as the return type.

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So we are simply returning object.

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Earlier it was wired.

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Other than that there is no difference here.

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So the pipe in foot.

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Once again we are passing string.

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So the type inferred is string.

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Right but the return type is also the type barometer B.

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Ok so the compiler knows that it is going to return a string.

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But in this case we are assigning it to a double.

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Right.

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On the string cannot be converted to debug.

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So compiler is is telling us that it is wrong assignment here so that this needs to be changed.

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So that's the compile time type safety benefit we get by using a genetic method.

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So this just demonstrates the compiler error.

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Not in this case we are displaying the compiler error but it highlights the fact that we are going to

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pass some wrong arguments.

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Ok so here we are using a method called audit collection which takes an ID and also a collection and

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copies all the elements of the Adinda collection.

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OK that's all it does on Hensick as named as outer to collection.

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So let's go ahead and look at this method.

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So here is the byte information be on.

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Here is the audio off of that pipe on here is a collection of the pipe.

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On here we are iterating through the elements of the array our days.

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And we are just adding that element as you can see here the pipe is deep and we're adding it the element

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all here always that element.

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We are adding it to the collection.

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That's all we are doing and first we are passing on in digerati and we're passing a collection off in

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major underbite.

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If you'll see it just be right.

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So it should be inferred ASC-P.

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So if I over it it says in danger.

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So this is the type argument that is inferred and it is an integer array a mixed collection off into

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.

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So once again it is inferred from the arguments here.

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Now if I change your train so we get our completion at her right we get a compilation here because I

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would not be in for it but because this is an integer and this is a string.

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But we were supposed to how as single type single type needs to be inferred.

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And that is not possible because this is integer and district but if I change this to number then it

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will be inferred as a number.

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And that's because between digit a number numbers the supertype most common supertype And in this case

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this is in court.

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We also discussed that in the lecture so set.

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So that's a bug in coding from the method arguments but if method arguments are not there are not specified

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then we know that it can also infer from the target type.

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And this is what is demonstrated here.

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OK so let's ignore this method name.

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Huge matter.

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But to say that we are inserting from target type.

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So if you look at this method it has a target type it has a method return type is also B but the method

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does not or does not use any method parameters.

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So inference has to be from the target type.

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OK.

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So if you go back.

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So if I hover over it it says that string is that type that is inferred.

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Now here in this case you see here in this case it is integer that Ogger type is integer.

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So B would be in for integer.

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But the only thing is if I wanted to get a compilation error I will get a runtime exception because

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this method is actually returning a string but the compiler is going to insert a cast here saying that

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it is integer because that's what it inferred from the target.

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OK so if I had run it probably this is the only time you run it.

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So we get a classic exception because Djalma long line docstring which was found here to be returned

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cannot be Casta Gelada or $9.9.

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OK so the compiler is going to insert ghast like this internally into a bytecode Mogami.

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So that's about that.

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So here the target pipe is being used but sometimes this kind of a motard can be part of another method

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invocation.

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So here we have a target type in Wilker one which is a method and to this method as an argument we are

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passing we are invoking this method.

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So this method does not have any method parameters here so it has two method arguments so it needs to

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.

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It needs to infer but that is not target type 2.

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So in this case it would it would infer from the method in Wookey shouldn't context.

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And we will see what that is.

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But that works on me from July 8 onwards are not going to work in all the motions before July 8.

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So I guess this is just the same at but the method name and Smith do.

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This ends with one.

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So let's just look at what this method is.

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So it takes it.

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Be here.

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This is the type under written by is a list of a.

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And it does something here let's not worry about it.

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But the return type is list offbeat.

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OK.

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Now if we go back if we look at this matter type target type in worker 1 it has a list off-Strip.

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OK this is a primary Kreiss type gander just done.

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Wired So the the method parameter list of string for this for on for this it is the return type is list

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off.

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So that list of B will be compared with the list of strik this one since this has a list of string as

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the method parameter now.

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So that acts like a target type and the compiler would infer the type argument of this method as B.

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But here it says a list of object are night that should be some bug within the eclipse Marsh which is

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the editor that I'm using because if it is a list of object and if this one is taking a list of string

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then that the assignment is not right.

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Right.

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That's because of invariance.

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So it's got to be a list of string only then it will work.

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If it was a list of string if it was something other than a list of string it would have shown a compiler

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error but it is not showing.

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So it should be a bug in a eclipse marsh.

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So that's what it is.

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Now let me just go ahead and change this properties and let me change this to 1.7 here.

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So it's not going to work anymore.

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So yes you can see it as giving some compilation orders here.

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OK.

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So it's not going to work so let's change it back to one point eight.

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OK.

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So that particular feature of inputting that kind of inputting was only introduced in Java 8 because

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go compilation error has gone on here it's just a similar thing and start off.

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This method we are creating an instance of idlest and we have the diamond notation.

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Now the diamond notation also uses the type argument here.

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But if it is not there then it would have used the target type.

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OK.

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Which is something like.

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Or at least all string equals Do you want a list off this one which we have been seeing in the in our

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demos.

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So that's not the case here because it is it is in-circuit it is added here in the method and location

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.

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So in this case also it works in the same way.

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This one takes a list of string so a string will be inferred here for this for this year for the generic

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type but unfortunately the same of the bug that we saw here also seems to be appearing here we are.

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We seem to have the same problem.

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OK.

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So that's about it.

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Now here we are in walking type argument inference from Target type 2.

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It's just the same method but here we are using a different type target type in walk or run.

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This is not a great typing marker do you get that.

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So this one uses list of the early articles list all string on it also written setlist offbeat but Gazzetta

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irrelevant.

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Solist offbeat so here.

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So this would be a list of the now.

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In this case it's a list of B.

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Right.

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So that type of this has to be inferred fast.

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OK but this is also not inferred.

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OK.

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There are two non inferred things here.

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So in this guess sense since it cannot be inferred because its argument is also not there and that is

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not archetype also for this method.

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So here the compiler places in it as object.

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OK if it cannot infer it will just keep it as object its what is happening here now here and this method

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is just the same invocation.

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But we have a target type here just off string.

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So if I holler at it it says that fart does matter type dargah typing work or do or does in court as

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strict.

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So it would become a list of string and then this one also because it has a list of B as the return

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type.

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So it will be in for a string but for this eclipse is not showing any is any issue.

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So it says that it is in for the string even for this.

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So for both of them are just string even for this method we are passing Nautilus off Diamond notation

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even for this its target type in walk or do.

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And for this also it will be a list of object.

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But in this statement We are using a target type on your list of string and we are having the new order

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list off this.

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So in this case it is going to infer as string.

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What about the method as well as for our list.

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And you can say as I know it is not strict only in this case because there is no way for us to infer

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it is seeing saying list of objects.

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OK so thats the thing.

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Now thats more ahead.

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And now this is another example of inferring the most specific supertype we saw this in the lecture

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.

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So this method has a beat and then return type is B and both the parameters are also using the type

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.

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So if you go back we are passing a string on another list here.

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If I hower Serializable is being in what we saw that in the lecture and this is also serializable.

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Now if it does something as like an integer then it is going to give us a combination error.

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So it needs to be serializable here because the return type is D.

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Now this is another example.

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Same things similar kind of thing.

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But we are passing out elist instance of list on an instance off a set here has said.

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So the common supertype is abstract collection.

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Implements collection.

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So thats why it is going great is footing as abstract collection here.

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So lets not worry about all this thing but it is basically abstract collection.

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And here we are calling it as useless generic method.

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Lets see why it does use you has.

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So if you go here this is the type parameter but the return type is void and the type parameter that

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is not a parameter here and the method parameter list.

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So basically it is pretty much we are passing it explicitly but it will not be used in any way in the

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client order right.

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Thats the benefit of genetics.

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Had it been if it was using editor type then it could have inserted a cast but thats not the case it

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is what are doing it under the parameters are also not there.

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So there is no scope of passing in arguments.

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So its just a list by parameter.

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So this is just to highlight the usefulness of parameters.

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So thats what it is ironed.

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Now let's ignore this for now.

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Not look at generally constrictors.

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So here is the genetics demo we are in that Benedix demo class.

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So lets look at these go here.

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So it uses this class level parameter b and this is the generics Demel generics constructor.

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And just like generic methods we are using this extents D.

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So it is easy for this I need is extending this class level by parameter and this is also used here

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as the parameter type.

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The thing is genetic constructors are very rare.

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I really did not find any examples for us.

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So I think we dont have to worry too much about it but the eldest class here it uses here are enlist

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he is a class level type parameter but this is a bonded bonded wild card.

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So it is using like this.

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We still did not discuss it or discuss bonded wild cards later but it can be converted into a genetic

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constrictor.

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But still this is the right way to do it.

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In this case so it does really relate to how genetic construct hurts.

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But this is just for your information.

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And this case.

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So here it is.

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So we have this we are instantiating genetics to them all.

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So this will be the pipe argument for the genetics demo class.

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OK.

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Now coming to the genetics constructor it will be inferred from the type argument just like genetic

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metrics.

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So it looks like genetic methods on a genetic constrictors we're going to limit that.

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So it is going to be for Howard what it is saying that that argument inferred from the constructor is

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double whereas for girls it is number no it is fine because doubleness going ekster number is futile

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.

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If you remember if you recall the constructor had the extents B.

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So B is number here which is a classloader type but done on E is double now in the next line here.

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So this one has a diamond notation under Diamon notation also uses repipe argument.

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OK so in this case this will be double here and the constructor also uses the type argument.

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So the type argument is used by both this notation but that I'm a notation as well as this.

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So it's like Hower says double here.

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It also says W here.

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Now here you are you're passing it explicitly you're passing double for the constructor but for the

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Class B a passing number that is perfectly valid because double extents number.

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So here everything is explicit.

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So that's pretty nice.

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So here you pass it this way.

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This is how you explicitly specify right before Gosney.

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You can also specified here just after the there need not be the space here.

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This also looks.

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Now here this is this I'm really not sure why this is so this is explicit but here this is supposed

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to be implicit.

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So I assumed that it would infer that automatically that this is a double.

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But it is not doing it are not.

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I wish it could have inferred better does not doing.

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So I really do not know why it does look as if I know what it says explicit type arguments cannot be

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used with a diamond notation in an allocation expression.

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So this is an allocation expression.

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So I don't know the reason for that.

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I know I did not find any not Hondas and I searched for that particular exception on in Google.

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I did not find any any anything about that.

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So let's just leave it like that.

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Now here is another example where the constructor for the constructor does inferring from here like

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it should from the method argument.

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But for this it is inferring from the target type because if it is first double it this is going to

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be generics and I'm off number then we have the invariance issue.

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So the compiler is smart enough to infer a number from this guy.

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So that's the thing.

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And here is the final thing.

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This is from.

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We saw this in the wild cards demo.

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So we had one less.

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OK.

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Then it was called as invalid agregate and we were aggregating the elements from this list from the

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second list into the list.

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So that to the three lists are surpassed here the the elements from the first on the second list here

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are inserted into this.

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And we know that in aggregate in reality that was a matter and you can go back and look at that because

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of me because we were using wild cards.

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It did not allow us to art here it was giving a compassionate heart because because of using the wild

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card game.

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But now we can add them.

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So that means that the common disorder I think it's this one.

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So as you can see this is all good.

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One two three and four.

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It's working fine.

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So that's all there is for that not only thing here.

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As I commented on this one this one we are also explicitly passing type witness here stood a monster

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.

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But here it's genetics Demel.

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It is supposed to be when you remove this you're just a monster tinga.

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OK.

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So in this case is.

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So in this case this is all compilation.

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Let's not worry about it.

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It's just demonstrate.

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I'm just a monster getting dark.

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This pipe argument inference I'm passing on explicit here.

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Preakness here.

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That's all there is.

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So if you look at Doc takes a beat on we're passing genetics demarche self.

328

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So that's why here I am passing an instance off in an accident.

329

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So that's all that is so then.

330

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My thoughts are really useful for static utility classes.

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If you have something really genetic reuseable algorithmic kind of methods which can work on any input

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then you need to go for that.

333

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And by inference is there.

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So that's about EQ.

335

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So it's really useful you need to favor genetic methods.

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OK.

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Thank you.

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Arne the code is available in the resources section.

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Happy coding.