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Hi there now that we know why language designers came up with Benedix let's not get started with the

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basics of genetics in this lesson.

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They will look at the syntax and terminology involved with genetics and also look at few restrictions

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associated with genetics in the Allison will lead them off genetics.

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Basically we do have them all off what we learned in this lesson.

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Let's begin by looking at genetic type a genetic type is simply a class or an interface that type but

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amateur's defined in the declaration on here is the basic syntax.

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So the class name is followed by something called type parameters which are camos operator are not enclosed

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in less than greater than symbols and within the class.

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These type parameters can be used as byte for instance variables by foot barometers on local variables

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within methods are constructors.

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And also ask method root types on here as an example from the previous lesson.

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The class store uses a single byte but I'm a dirt beat.

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And as you can see despite barometer is used just the type for the instance variable A as well as method

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parameter in the center.

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And also as a return type for the get.

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So we look at for the generic type s.

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Now let's see what a parameter is this.

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And also understand some Gentex terminology here at the top.

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We have the genetic type store and we know that B here is the type barometer and is also referred to

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as a formal type barometer under the bottom.

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We can also see that for instance this off store are created for instance is a store of string that

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is a string is stored in the stored instance that a string got response to that pipe barometer.

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Be in the store class.

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The second instance is a store off date.

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Third instance is a store off list of data that is store instance stores a list containing data objects

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unfought is stored off Brooke.

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You may recall that in collections framework we did something similar to create lists of string on a

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list of integers and so on.

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So listener interface is a generic type.

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Now here the reference by store of string is referred to as it parametrized by.

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So the whole thing store followed by string.

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But then the less done greater than symbiotes is up permit race type.

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OK.

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So we have the genotype on we have the parametrized type.

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OK so just keep that in mind on just the string is referred to as type argument.

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Our actual barometer.

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Now if you recall our introduction to them at lesson in the language basic series we had similar terminology

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method parameters were also called as formal parameters.

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Well arguments passed during method invocation were referred to as actual parameters so that it was

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formal parameters are natural parameters.

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And here it has formal parameters on actual type parameters.

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Because we are dealing with types no one thing to note as in the first three instance creation statements

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we have the right argument on either side of the assignment.

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How they would in the last week meant we have the type argument on the left side and on the right we

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how M.D less than greater than symbols.

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And this is called Diamond notation and it works only from July 7 onwards.

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In this case type is automatically inferred based on the types specified on the left side.

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So it is a shorthand so soit would be elegant to use this notation.

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Now let's look at the naming conventions for type parameters.

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You should definitely use a single uppercase letters and we can also see some conventions here.

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If you are writing some kind of a collection type class then you can use an E Where.

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E is for element.

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If you're writing a map then use gay for the unbe for value.

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If a generic type is dealing with numbers then you can use an and if your agenda type is a non-color

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action and is not about numbers then you can use it.

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B B would be the common one as generally B.

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Right.

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Non collection classes.

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Typically you would have only one type parameter but if you have more than one then you can use s u

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and v for the second third and fourth types just like SUV.

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I don't think he will ever go beyond forth on even if you do you can use some other character.

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Generally you can use any legal Jawa identifier but stick to this convention and this slide shows how

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a generic type can be subduct on the left.

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We have a generic interface called container.

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Right.

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We have the genetic Glassdoor which we saw earlier.

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But in this case it implements the generic interface container on here and in an offbeat in the class

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declaration of store is basically parameterized type on we can create an instance of storing this it

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reference type is the generic interface container all the interfaces we saw in collection's framework

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API are also gentrify and you may recall that we weren't instantiating their implementations in this

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way.

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For instance you referenced type would be a list of something or not right.

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We would have something like an analyst in the demo that we will do in the next lesson we will implement

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this court and we will also look at a couple of other things around subtyping.

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This example just shows a generic class with multiple type parameters.

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If we assume that all store class works like a map then it would look something like this.

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VB What how parameters can be which will be used in different places within the classes body here can

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be are used just pipes for key and value variables and then also used as constructor parameters and

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also as written by IPS in the methods get the and get value nowness look at couple of core restrictions

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that are associated with genetics and later in the chapter.

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They will also look at few more restrictions here the restriction is that the type argument cannot be

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remedied.

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In this example the type argument is and it would give us a compiler error.

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Similarly another restriction is doc type barometer cannot be used in a static context.

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For instance it cannot be used as a type for stocktake Williams.

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Here we have a generic class called device and we can see that static variable device type has the right

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barometer B as that.

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And this is illegal.

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Lets see why this is illegal.

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Do I understand it.

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Let's assume that it is legal to define a static variable with that type barometer.

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Here we have these two statements where we are creating two instances of device in the first instance

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that type argument is smartphone while in the second that type argument is bigger.

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Another question we can have is what would be after both these statements are executed.

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Would it be smartphone or would it be pager.

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If we assume that it would be pager just because it was the last it meant to be executed then the assumptions

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made by the developer who wrote the first statement might become invalid for example double up on who

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wrote the false statement would expect the type to remain stocktake when he Bassa smartphone on some

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other code of his word expect the same.

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Now if it gets changed to a pager then it could result in some undesirable behavior.

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And that is the reason type barometer is not allowed to be used in this way since we are talking about

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stocktake context by parameter.

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Obviously cannot be used in a static method or in a static initializer.

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So thats about it for now.

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And as I mentioned earlier we will look at fuel more restrictions later after covering some relevant

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concepts.

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Thank you.

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Our next move is more of what we learned and this lesson