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The last step is to bulletproof the application, in other words, working to make sure the application

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doesn't fail or crash no matter what.

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All right, let's run the up.

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And the first vulnerability in the opposite, the user enters a blank name or phone number.

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The constructor is going to throw in a legal argument exception once again, this is an unchecked exception

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because it occurs during the runtime, but under no circumstance should be let the application crash.

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If we get an unchecked exception, that means there's something wrong or there's something missing in

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your code.

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And what's missing in this case is code that anticipates a scenario where the user may enter a blank

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name or phone number, so we'll say if name DOT is blank or if the number they pass on is blank.

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Then we'll just print the input you provided is not valid registration, fáilte.

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Otherwise, we can add the contact.

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If you run the app.

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Good.

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But another illegal argument exception crashes the app if the user enter the phone number, that's less

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than five characters.

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Once again, an unchecked exception implies we're missing something in the code.

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And all we gotta do is check if the phone number is less than five characters, then we're going to

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tell the user that their input is not valid.

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And with this final line of code, proud to say that we're all finished.

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Just like that, our application is bulletproof, no matter what the user throws at you, the application

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is free of bugs and it's never going to crash.

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It can process any input and respond accordingly.

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In the end, exception handling, which involves catching checked exceptions and fixing unchecked exceptions,

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is the key to building bulletproof applications.