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It's important to throw unchecked exceptions to maintain quality control.

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In this lesson, you're going to learn how to throw unchecked exceptions.

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First off, follow this path in your resources and open the folder, throwing exceptions, and if you're

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missing this path, please download the updated resources from GitHub.

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OK, before we start, we're going to place every class that models and object into a package named

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models.

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The reason I'm doing this is because I want to have a clear separation between classes that model an

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object and the main class where we create objects.

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All right, now, if you allow Vasco to refactor, it's going to import the classes for you, which

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is perfect, but for learning purposes, we're going to do it ourselves.

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So inside main, we get a whole lot of errors because it doesn't recognize the employee or the store

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class.

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That's because they're in a different folder and it can't find them.

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So we need to import them.

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So go to your model classes and at the very top.

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We're going to write package models, this line specifies the folder that outclasses in.

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You know, back in Maine, we can impart the class.

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Import models, that employee.

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And we can also import models that store.

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Now, if you want to import every clause inside the model's folder, you can also write import models

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that start.

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The star basically grabs every single file inside the model's folder.

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The syntax is also available in your cheat sheet.

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But for the sake of simplicity, I'm just going to impart the classes separately.

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OK, let's run the code.

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And the store opens without any employees, the caller, the person whose programming, the main method,

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they're misusing the methods and constructor's from each model.

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This leads us to why do we throw unchecked exceptions, we throw unchecked exceptions that prevent the

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caller from misusing methods or constructor's.

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In other words, you should throw unchecked exceptions to maintain quality control.

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And the most common, unchecked exceptions that you're going to throw are a legal argument exception,

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an illegal state exception, they act as checkpoints to make sure the programmer fixes their code.

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So inside Maine, the caller's passing is null and blank values into the employee constructor, they're

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creating three employee objects with values that don't make any sense.

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We're going to visualize the runtime.

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And you can just tell how awkward this looks and that employees shouldn't have blank names and no positions,

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every employee in the store must have a concrete name and position.

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So in the constructor, we're going to check if the name or position is null or blank, if name is equal

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to null.

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Or if the name is blank.

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Or if the position that was passed in is No.

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Or if it's blank.

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Then we're going to throw a new legal argument, exception.

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And then as we cross the application, we're going to tell the caller the name or position cannot be

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Neller blank.

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This is like a checkpoint, it's going to force the caller to fix their code, we're basically telling

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the caller, hey, man, if you want to use my constructor, you better pass incorrect correct values.

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We're throwing an unchecked exception to inform the color of their badly written code.

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Attempting to run this code.

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Results in a crash.

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Stepping in, stepping out.

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And stepping back in.

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The caller gets all the way here with the values they pastan.

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But at this point, the instructor says not so fast and throws an illegal argument exception, crashing

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the application.

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And now the color ideally is going to recognize this failure as an unchecked exception because it happened

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during the run time and they'll say, oh, OK, I got to fix my code.

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In this case, we're forcing them to pass incorrect values.

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So as the caller myself, I'm going to pass in the following values.

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Paul, he's going to be the stalker.

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Nicholas, the assistant manager.

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And Damian as the manager.

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All right, we're running the code.

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And get.

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Now, should the copy constructor throw exceptions, usually no, because the source object repass again,

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it was already created with the first constructor.

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So we can assume that all of its values are good.

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Like, for example, let me make a copy of the stalker object.

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Step into the copy constructor.

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All the values are going to be good because they went through the first constructor, so we don't have

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to worry about any illegal values.

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But what if the user passes a null into the copy constructor, surely that's not legal.

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Well, let's see what happens.

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And beautiful, the copy constructor already throws a null pointer exception, which forces the caller

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to fix their code so us throwing an illegal argument exception would just be redundance.

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All right, let's talk about the illegal state exception, this one is thrown if an object calls a method

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with an illegal status.

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In other words, you need to throw an illegal state exception if an object isn't properly initialized

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before calling a method.

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In this case, I'll put a few break points here.

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We're on the debugger.

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And you can see the store object doesn't have any employees, and so we can't allow the store to open

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unless it hires enough employees.

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The store is not in a valid state to call the open method.

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So you're going to create a for loop that runs through the length of the employees field.

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And if any of the elements are No.

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We're going to throw an illegal stain exception and tell the caller whoever is calling this method.

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You must be fully staffed before opening the store.

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Attempting to run this code or result in a crash.

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The color created a store object, but didn't update the employees from the store object.

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They tried to call the open method, but they're calling it with an illegal status.

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So our checkpoint inside the open method crafted the application.

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The color is going to recognize this failure as an unchecked exception and say, OK, I got to fix my

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code in this case, we're going to call the Senate three times and update every element with an object.

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And once all the positions are filled, only then are we allowed to open the store.

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And beautiful.

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So hope you can see that each checkpoint forces the programmer to call the methods or the constructor

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properly.

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In this lesson, you learn to throw unchecked exceptions.

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You should throw exceptions to forbid the caller from misusing methods or constructor's.

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Most common contact exceptions that you will throw are a legal argument exception, an illegal state

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exception, you should throw an illegal argument exception if a constructor or method receives a legal

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values.

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You should throw an illegal exception if an object calls a method with an illegal status, if it calls

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the method at a bad time.