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Not let's look at casting off objects or after discussing casting they will also look at a new operator

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card instance or we look at typecasting during our discussion on primary variables.

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It allowed us to assign primitive variables all the close of one by two variables off another type.

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And it's because both implicit as well as explicit casting implicit casting is done when something smaller

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is assigned to a larger variable unexposed casting is needed when something larger is assigned to a

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smaller variable.

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Just recall that typecasting was applicable only if both data types but often your Model X that is any

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good or type other than Boolean.

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So by casting what's needed as one pyramided variable to run would be assigned to another variable and

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we saw that with polymorphism we can now assign variables of 1 class two variables of another class

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.

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And we also need gasping here.

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Now we looked at this example when introducing polymorphism.

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In fact it is a very definition of polymorphism of polymorphism.

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We are able to pass a subclass object as argument with a method parameter which is off by superclass

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.

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So basically what we are seeing here is implicit casting in action.

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That is a separate object is implicitly cast it with a superclass variable.

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But once implicit casting is done VIGEN only in work DOS subclass methods which are also defined in

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the superclass.

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That is we cannot in any method that are specific to subclass were discarded when introducing polymorphism

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.

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And here is an example cross implicit cast is done to assign editor object to a gray area.

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Will I stop you know that editor is it some pipe office.

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Once this is done we can no longer invoke any methods that are specific to Ed. And we know that this

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is because compiler uses referenced type to decide on whether meathook can be involved or not.

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So here we get compiler error as the reference type stuff does not how it would have matter to exist

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.

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We need to insert a digger as an explicit cast as shown here.

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Now we are promising compiler that at runtime the variable s been referencing an editor object or one

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off it's a process in invoke the method we need to parse or parenthesis one with the cast itself on

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the other on the cast and a variable.

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Now this example is same as the previous one but it is ex-POWs in a more realistic way.

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Here the matter a prove review has staff as input parameter and it in turn will prove to be a third

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on the input stuff object which we know gives a compiler and do what does we insert editor as an explicit

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ghast.

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So as mentioned earlier by inserting this ghast we are promising the compiler that at runtime the variable

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as well be referencing an editor object.

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Now see if this method is invoked with a stop object that is we are breaking the promise we made to

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the compiler.

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Now with this we get an error at runtime and this error is called Class Guste exception.

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That is the input object and not because it a specific class that is.

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And this gives the staff object cannot be trusted to editor and this is because staff can be an editor

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but it can be something else too.

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For instance it can be an email admin too.

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So while it is a staff a staff need not be editor.

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And so we get this error at runtime.

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Now one thing we can do.

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What does run by matter is to be a logical test before doing the cast on product.

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We could use something called an instance of operator.

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And here's the syntax on the left.

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You have an object reference on that right.

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We have the name of the class instance of operator operate in a group.

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If the object referenced by the object referenced on the left is indeed an instance of a class on the

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right not that it is the object references object not the reference type is what matters.

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So just take that in mind.

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Also the object referenced by the Brady bill can be a subclass of the class specified on the right side

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.

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So it doesn't have to be a direct instance not just look at some instance of examples let's consider

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this through declarations just one second instantiate user On-Star classes.

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Well the third one creates an instance of staff but the reference type is user.

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And this example is related to the declaration since a variable use object type is user it is an instance

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of user.

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And hence it truly is written in this case.

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This expression returns false as use object type is user which is not an instance of stuff.

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And we know that stuff is a subtype of user.

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And this is related to the second declaration here.

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Object type or variable.

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As is stuff.

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So this evaluates to true this would also evaluate to true as sort of rinsing as stuff objects and stuff

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.

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Is this a type of user.

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So as we mentioned earlier the object reference can be a subclass of the class on the right side of

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the instance of operator like in the previous example.

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This also evaluates to true as the variable us in the third declaration is referencing stuff object

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type which is a subclass of user.

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And the final example also evaluates to true as it is the object type that matters.

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And here is a new rule review mattered which prevents the potential runtime error.

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It does if the input variable as is an instance of editor.

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Only if the test succeeds.

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It applies to cast on in walks not approved method.

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So we cannot use these kinds of invocation statements.

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The test place for the frost in location where a staff object is being passed us argument until the

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run parameter is presenter.

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But the best succeeds for both the second and even the third in location where Chief Editor object is

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passed and we know that Chief Editor is a subtype of editor.

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Now let's go ahead and look at all of the stuff we learned in court.

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This is a prove review method and it has been added to the user test class which has been created in

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the previous demo.

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And here is the final logic that we have seen in the slide.

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But I'm going to start with the demand starting from the beginning the concepts that we have started

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learning from the beginning of the lesson.

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So initially we were in walking it prove review method.

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So the input we able to this method is staff and be ready in working a prove review.

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And it was a compilation error because the compiler knows that a proper review method is not in the

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staff class.

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So we said the compiler looks at the reference with you but not the object but the reference variable

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.

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And in this case a reference variable is staff and it doesn't have the approval of your mentor.

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So we get a compiler error when I holler over here it says I'm at a poor review is undefined.

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So let me just comment this out and the solution was to insert a cast.

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And so here we are applying this cast we are inserting this editor as a cast.

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I know it works.

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So we don't see the competition either.

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So let's just run this.

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So we are in working we have created in an instance of the user base class and we are invoking the approval

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of your method but we are invoking word by passing staff object Asom motard argument.

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So this would give us a runtime error.

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So when I run this as we discussed it is doing class cost exception.

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So that's a runtime error that we're getting here.

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So it's no longer it's not a compilation error but it's a runtime error on says that the error is happening

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at line 11.

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So this is where the casket is being applied.

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And we were passing a Stav object instead of passing an editor object or one of its subtypes.

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We promised the compiler that we would be passing either an editor object or one off its up.

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And we did not do that.

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And so we are getting this runtime error.

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So now to avoid this we said we can use instance of operator and we did that and this is the logic.

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So let me just uncommon discord.

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So here we are applying the instance of operator and if it is really an instance of a date or one off

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it's subclasses then we were in Roeg this method we would apply the cast on in this.

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Otherwise we would simply print this statement invalid object passed.

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So now if we invoke this it is invalid object passed when we are passing stuff.

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So let me comment this on that we pass an editor object.

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So and I run this it's this editor a pro what have you.

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So it's actually invoking a prove review method in editor class.

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So.

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So it is going here and it is invoking a proper review method and the reader class.

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So probably you are and it is going to print this statement.

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This this text.

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So that's about it.

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And once again I'm showing this a gym or an eclipse to sip some time.

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And you you know you can download discorporate in the resources section and you can buy it in your or

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whatever editor you are using on you contested