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In this solution, we're quality control the store class, we need to forbid the caller from misusing

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the methods or the constructor, the constructor doesn't receive any parameters.

3
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So there's nothing to check here.

4
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There is nothing to quality control in the setar, because if the caller happens to pass a no instead

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of an actual object, the code would already throw a nail pointer exception.

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So throwing our own exception would be redundant.

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The same thing can be said for ad movie.

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However, there's a lot to quality control in the action, first of all, if the store object doesn't

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have any movies, then it's not an illegal state to call the method.

10
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You can't return, sell or rent a movie that doesn't exist.

11
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So here, we'll say if movies, that is empty.

12
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We'll throw a new.

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Illegal state exception.

14
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Store not in a valid state to perform action.

15
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One more thing we want to check is that the action they want to perform can only be one of three things

16
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sell, rent or return.

17
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So if the caller passes anything else, we need to throw an exception.

18
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So if the auction they pass, if it doesn't equal sell.

19
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Or if it doesn't equal rent.

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Or if it doesn't equal return.

21
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Then we'll throw a new illegal argument exception.

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Action must be sell, rent or return.

23
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All right, and the color shouldn't be allowed to pass a name that's blank, so if the name is equal

24
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to No.

25
00:02:12,180 --> 00:02:13,890
Or the name is equal to blank.

26
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We'll throw a new illegal argument exception.

27
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Name Kaname Neller Black.

28
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And the last thing we're going to do is forbid the caller from trying to sell a movie that has already

29
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been rented.

30
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So inside, so we're going to check if the movie at the index.

31
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That was a request that is not available.

32
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Then we're going to throw a new illegal state exception, because the state of the movie object that

33
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we're trying to sell is inappropriate for this operation.

34
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We'll just say cannot sell a movie that was rented out.

35
00:03:13,380 --> 00:03:18,330
And that's all the quality control we need to apply and now this method is going to forbid the caller

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from misusing it, if the caller does misuse it, their application is going to crash and they're going

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to have to fix their code.